Vb.net Notes

04/08/23 1

NAVGUJARATCOLLEGE OF COMPUTER APPLICATIONSSubject:Advance visual and windows programming(BCA-205)

PRESENTATION ON VISUAL BASIC .NET

04/08/23 NAVGUJARAT COLLEGE OF COMPUTER APPLICATIONS Kaushar Ghanchi

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.NET Defined

Before getting deeply into the subject we will first know how Businesses are related to Internet, what .NET means to them and what exactly .NET is built upon. As per the product documentation from a Business perspective, there are three phases of the Internet. The First phase gets back to the early 1990's when Internet first came into general use and which brought a big revolution for Businesses. In the First phase of the Internet Businesses designed and launched their Website's and focused on the number of hits to know how many customers were visiting their site and interested in their products, etc. The Second phase is what we are in right now and in this phase Businesses are generating revenue through Online Transactions. We are now moving into the Third phase of the Internet where profit is the main priority. The focus here is to Businesses effectively communicate with their customers and partners who are geographically isolated, participate in Digital Economy and deliver a wide range of services. How can that be possible? The answer, with .NET.


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What is .NET ?

Many people reckon that it's Microsoft's way of controlling the Internet, which is false. .NET is Microsoft's strategy of software that provides services to people any time, any place, on any device. An accurate definition of .NET is, it's an XML Web Services platform which allows us to build rich .NET applications, which allows users to interact with the Internet using wide range of smart devices (tablet devices, pocket PC's, web phones etc), which allows to build and integrate Web Services and which comes with many rich set of tools like Visual Studio to fully develop and build those applications.


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What are Web Services?

Web Services are the applications that run on a Web Server and communicate with other applications. It uses a series of protocols to respond to different requests. The protocols on which Web Services are built are listed below:

UDDI: Stands for Universal Discovery and Description Integration

WSDL: Stands for Web Services Description Language

SOAP: Stands for Simple Object Access Protocol XML, HTTP and SMTP


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EDITIONS OF VB .NET

Academic Edition Professional Edition Enterprise Developer Edition Enterprise Architect Edition


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Types Of Projects

Windows Applications Class Libraries Windows Control Libraries Smart Device Applications Asp .Net Web Applications Asp .Net Web Services Asp .Net Mobile Web Application Web Control Library Consol Application Windows Services


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TYPES OF FILES AND THEIR EXTENSIONS .Suo Solution User Option File .Vb Any File From Following

A Basic Window Form A Code File A Module File For Storing Functions A User Control As Data Form A Custom Control An Inherited Form A Web Custom Control An Inherited User Control A Window Services An Assembly Info File


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.Xsd An Xml Schema Provided To Create Datasets .Htm An Html Document .Txt A Text File .Xslt An Xslt Stylesheet File .Css Cascaded Stylesheet .Rpt Crystal Report .Bmp Bitmap File .Js Jscript File .Vbs Vbscript File .Wsf Windows Scripting File .Aspx A Web Form .Asp An Active Server Page


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.Asmx Web Service Class .Vsdisco A Dynamic Discovery Project .Web A We Configuration File .Asax A Global Application Class .Rex A Resource File To Store Resource

Information .Sln Solution File .Vbproj Vb Project File .Vbproj.User Vb Project User Option File


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VB .NET IDE Start Page Menu Bar Toolbars New Project Dilogbox Object Browser The Toolbox The Solution Explorer Class View Window Property Window Dynamic Help Window Component Tray The Server Explorer


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The Output Window The Task List The Command Window Graphical Designers Form Designers Web Form Designers Component Designer Xml Designeres Code Designers


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MODES OF VB .NET

Design Time Mode Runtime Mode Break Time Mode


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VB Language

Visual Basic, the name makes me feel that it is something special. In the History of Computing world no other product sold more copies than Visual Basic did. Such is the importance of that language which clearly states how widely it is used for developing applications. Visual Basic is very popular for it's friendly working (graphical) environment. Visual Basic. NET is an extension of Visual Basic programming language with many new features in it. The changes from VB to VB .NET are huge, ranging from the change in syntax of the language to the types of projects we can create now and the way we design applications. Visual Basic .NET was designed to take advantage of the .NET Framework base classes and runtime environment. It comes with power packed features that simplify application development.


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Namespaces

A namespace is a collection of different classes. All VB applications are developed using classes from the .NET System namespace. The namespace with all the built-in VB functionality is the System namespace. All other namespaces are based on this System namespace


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Some Namespaces and their use:

System: Includes essential classes and base classes for commonly used data types, events, exceptions and so on

System. Collections: Includes classes and interfaces that define various collection of objects such as list, queues, hash tables, arrays, etc

System. Data: Includes classes which lets us handle data from data sources

System.Data.OleDb: Includes classes that support the OLEDB .NET provider


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System. Drawing: Provides access to drawing methods

System.IO: Includes classes for data access with Files

System. Threading: Includes classes and interfaces to support multithreaded

System. Web: Includes classes and interfaces that support browser-server

System.Windows.Forms: Includes classes for creating Windows based forms


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Assemblies

• An assembly is the building block of a .NET application.

• It is a self describing collection of code, resources, and metadata (data about data, example, name, size, version of a file is metadata about that file).

• An Assembly is a complied and versioned collection of code and metadata that forms an atomic functional unit.


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• Assemblies take the form of a dynamic link library (.dll) file or executable program file (.exe)

• Assemblies are made of two parts: manifest, contains information about what is contained within the assembly and modules internal files of IL code which are ready to run

The assembly file is visible in the Solution Explorer window of the project.


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DataTypes

Data Type Size in Bytes Byte 1 8-bit System.ByteChar 2 16-bit System.CharInteger 4 32-bit System.Int32Double 8 64-bit System.DoubleLong 8 64-bit System.Int64Short 2 16-bit System.Int16


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Contd..

Single 4 32-bit System.Single

String Varies Non-Numeric System.StringDate 8 System.Date

Boolean 2 Non-Numeric System.BooleanObject 4 Non-Numeric System.ObjectDecimal 16 128-bit System.Decimal


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Access Specifiers

1. Public: Gives variable public access which means that there is no restriction on their accessibility

Private: Gives variable private access which means that they are accessible only within their declaration content

Protected: Protected access gives a variable accessibility within their own class or a class derived from that class


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Friend: Gives variable friend access which means that they are accessible within the program that contains their declaration

Protected Friend: Gives a variable both protected and friend access

Static: Makes a variable static which means that the variable will hold the value even the procedure in which they are declared ends

Shared: Declares a variable that can be shared across many instances and which is not associated with a specific instance of a class or structure


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Variables

Variables are used to store data. A variable has a name to which we refer and the data type, the type of data the variable holds. VB .NET now needs variables to be declared before using them. Variables are declared with the Dim keyword.

Dim stands for Dimension.


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Example of variable

Dim a,b,c as Integer'declaring three variables of type integera=10b=20c=a+bWrite("Sum of a and b is" & c)End Sub


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Statements

A statement is a complete instruction. It can contain keywords, operators, variables, literals, expressions

and constants. Each statement in Visual Basic should be either a declaration

statement or a executable statement. A declaration statement is a statement that can create a variable,

constant, data type. They are the one's we generally use to declare our variables. On the other hand, executable statements are the statements that

perform an action. They execute a series of statements. They can execute a function, method, loop, etc.


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Option Statement

The Option statement is used to set a number of options for the code to prevent syntax and logical errors. This statement is normally the first line of the code. The Option values in Visual Basic are as follows.

Option Compare: You can set it's value to Text or Binary. This specifies if the strings are compared using binary or text comparison operators.


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Contd…

Option Explicit: Default is On. You can set it to Off as well. This requires to declare all the variables before they are used.

Option Strict: Default is Off. You can set it to On as well. Used normally when working with conversions in code. If you want to assign a value of one type to another then you should set it to On and use the conversion functions else Visual Basic will consider that as an error.


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Explicit Conversions

When types cannot be implicitly converted you should convert them explicitly. This conversion is also called as cast. Explicit conversions are accomplished using CType function.

CType function for conversion If we are not sure of the name of a particular conversion function then we can use

the CType function. The above example with a CType function looks like this: Imports System.ConsoleModule Module1Sub Main()Dim d As Doubled = 132.31223Dim i As Integeri = CType(d, i)'two arguments, type we are converting from, to type desiredWriteLine("Integer value is" & i)End SubEnd Module


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Explicit Conversions

CBool - use this function to convert to Bool data type CByte - use this function to convert to Byte data type CChar - use this function to convert to Char data type CDate - use this function to convert to Date type CDbl - use this function to convert to Double data type CDec - use this function to convert to Decimal data type CInt - use this function to convert to Integer data type CLng - use this function to convert to Long data type CObj - use this function to convert to Object type CShort - use this function to convert to Short data type CSng - use this function to convert to Single data type CString - use this function to convert to String data type


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Operators

Visual Basic comes with many built-in operators that allow us to manipulate data. An operator performs a function on one or more operands. For example, we add two variables with the "+" addition operator and store the result in a third variable with the "=" assignment operator like this: int x + int y = int z. The two variables (x ,y) are called operands. There are different types of operators in Visual Basic and they are described below in the order of their precedence


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Arithmetic Operators

Arithmetic operators are used to perform arithmetic operations that involve calculation of numeric values. The table below summarizes them:

Operator Use ^ Exponentiation - Negation (used to reverse the sign of the given value,

exp -intValue) * Multiplication / Division \ Integer Division Mod Modulus Arithmetic + Addition - Subtraction


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Concatenation Operators

Concatenation operators join multiple strings into a single string. There are two concatenation operators, + and & as summarized below:

Operator Use

+ String Concatenation

& String Concatenation


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Comparison Operators

A comparison operator compares operands and returns a logical value based on whether the comparison is true or not. The table below summarizes them:

Operator Use = Equality <> Inequality < Less than > Greater than >= Greater than or equal to <= Less than or equal to


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Logical / Bitwise Operators

The logical operators compare Boolean expressions and return a Boolean result. In short, logical operators are expressions which return a true or false result over a conditional expression. The table below summarizes them:

Operator Use Not Negation And Conjunction AndAlso Conjunction Or Disjunction OrElse Disjunction Xor Disjunction


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Arrays

Arrays are programming constructs that store data and allow us to access them by numeric index or subscript. Arrays helps us create shorter and simpler code in many situations. Arrays in Visual Basic .NET inherit from the Array class in the System namespace. All arrays in VB as zero based, meaning, the index of the first element is zero and they are numbered sequentially. You must specify the number of array elements by indicating the upper bound of the array. The upper bound is the numder that specifies the index of the last element of the array. Arrays are declared using Dim, ReDim, Static, Private, Public and Protected keywords. An array can have one dimension (liinear arrays) or more than one (multidimensional arrays). The dimensionality of an array refers to the number of subscripts used to identify an individual element. In Visual Basic we can specify up to 32 dimensions. Arrays do not have fixed size in Visual Basic.


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The following code demonstrates arrays. Module Module1Sub Main()Dim sport(5) As String'declaring an arraysport(0) = "Soccer"sport(1) = "Cricket"sport(2) = "Rugby"sport(3) = "Aussie Rules"sport(4) = "BasketBall"sport(5) = "Hockey"'storing values in the arrayWriteLine("Name of the Sport in the third location" & " " & sport(2))'displaying value from arrayEnd SubEnd Module


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Array Declaration

To declare a single-dimensional array variable In your declaration, add one pair of parentheses after the variable name, as in the following example: Dim MySingleArray() As Integer

To declare a multidimensional array variable In your declaration, add one pair of parentheses after the variable name and place commas inside the parentheses to separate the dimensions, as in the following example: Dim My4DArray(,,,) As Short ' Four-dimensional array.

To declare a jagged array variable In your declaration, add as many pairs of parentheses after the variable name as there are levels of nested arrays, as in the following example: Dim MyJaggedArray()()() As Byte ' Array of arrays of Byte arrays.


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Initializing Arrays

Specify the initial length of one or more of the dimensions in the parentheses following the variable name, without assigning an array object to the variable.

Assign an array object to the variable, using the New clause. When you use a New clause, you must follow it with braces ({}), even if they are empty.

Assign an array object to the variable and supply initial lengths in the New clause.

Assign an array object to the variable and supply initial element values in the New clause. You can supply both lengths and values in the same New clause.


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Examples of initialize array

Dim A(2) As Byte ' Currently contains Nothing (no object). Dim A(2) As Byte = New Byte() ' INVALID (New after length

specified). Dim A() As Byte = New Byte() {} ' Empty Byte array object. Dim A() As Byte = New Byte() ' INVALID (missing braces). Dim A() As Byte = New Byte(2) ' INVALID (missing braces). Dim A() As Byte = New Byte() {0,1,2} ' (0) through (2). Dim BA() As Byte = New Byte(2) {0,1,2} ' (0) through (2).


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Resizing Arrays

You can resize an array at any time by assigning a different array object to the same array variable, using either ReDim . The new array object can have different dimensions, although it must retain the same rank. For example, you can use a large array for a short time and then ReDim it to a smaller size. This frees up memory you no longer need.

When you ReDim an array, its existing values are normally lost. However, you can retain them by including the Preserve keyword in the ReDim statement. For example, the following statement allocates a new array,

ReDim Preserve MyArray(10, 20) In a multidimensional array, you can change only the last

dimension when you use Preserve. If you attempt to change any of the other dimensions, a run-time error occurs. If you do not know the current size of a dimension, you can use the GetUpperBound method, which returns the highest subscript value for the dimension you specify.


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CONTROL STATEMENTS

IF condition THENELSEIF condition THENELSEEND IF SELECT CASE exprCASE exprlst1CASE exprlst2….….CASE exprlstNEND SELECT SWITCH(expr-1,value-1,expr-2, value-2,..expr-N,

value-N) CHOOSE(index,chice-1, chice-2, chice-3…. chice-N)


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LOOPING CONSTUCTS DO while/until conditionStmtExit do

LOOP for index=start to end stepStatementsExit forNEXT WHILE conditionStatementsWEND WITH objectStatementsEND WITH


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Menus,Sub Procedures,Sub Functions Writing General Procedures Creating Menus and Menu Items Creating ContextMenus Displaying Common Dialog Boxes


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Sub procedures

A Sub procedure is a series of Visual Basic statements enclosed by the Sub and End Sub statements. Each time the procedure is called, its statements are executed, starting with the first executable statement after the Sub statement and ending with the first End Sub, Exit Sub, or Return statement encountered.

A Sub procedure performs actions but does not return a value. It can take arguments, such as constants, variables, or expressions, that are passed to it by the calling code.


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Contd…

The syntax for declaring a Sub procedure is as follows: [accessibility] Sub subname[(argumentlist)]

' Statements of the Sub procedure go here.

End Sub

The accessibility can be Public, Protected, Friend, Protected Friend, or Private.

You can define Sub procedures in modules, classes, and structures. They are Public by default, which means you can call them from anywhere in your application.


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Argument Declaration

You declare each argument for a procedure the same way you declare a variable, specifying the argument name and data type. You can also specify the passing mechanism, and whether the argument is optional.

The syntax for each argument in the argument list is as follows:

[Optional] [ByVal|ByRef] [ParamArray] argumentname As datatype

If the argument is optional, you must also supply a default value in its declaration, as follows:

Optional [ByVal|ByRef] argumentname As datatype = defaultvalue


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Calling Syntax

You invoke a Sub procedure explicitly with a stand-alone calling statement. You cannot call it by using its name within an expression.

The calling statement must provide values for all arguments that are not optional, and it must enclose the argument list in parentheses.

If no arguments are supplied, you can optionally omit the parentheses.

The use of the Call keyword is optional also. The syntax for a call to a Sub procedure is as

follows: [Call] subname[(argumentlist)]


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Example of sub

Sub sumofnos(ByVal a as intege,b as integer) Dim c as integer

C= a+b

MessageBox.Show(“sum of" & a & " and " & b & “is “ &c)

End Sub

Call this procedure as

Call sumofnos(10,20)


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Visual Basic program building blocks

Visual Basic code is stored in project modules. Projects are composed of files, which are compiled into applications. When you start a project and open the code editor, you see some code already in place and in the correct order. Any code that you write should follow this sequence:

Option statements Imports statements The Main procedure Class, Module, and Namespace, if applicable,

statements


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Function Procedures

A Function procedure is a series of Visual Basic statements enclosed by the Function and End Function statements. Each time the procedure is called, its statements are executed, starting with the first executable statement after the Function statement and ending with the first End Function, Exit Function, or Return statement encountered.

A Function procedure is similar to a Sub procedure, but it also returns a value to the calling program. A Function procedure can take arguments passed to it by the calling code, such as constants, variables, or expressions.


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Contd…

The syntax for declaring a Function procedure is as follows:

[accessibility] Function functionname[(argumentlist)] As datatype

' Statements of the Function procedure.End Function

The accessibility can be Public, Protected, Friend, Protected Friend, or Private.


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example

New Return statement

Can still set function name to value Better to use the Return statement

Private Function CalculateSum( _ByVal intNum1 As Integer, _ByVal intNum2 As Integer) As

Integer Return intNum1 + intNum2

End FunctionCalling the functionC=calculatesum(10,20)


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Menus

Create a menu by adding a MainMenu control to the component tray

Great new Menu Designer replaces the Menu Editor


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Menus

For Context menus, add a ContextMenu control

A ContextMenu uses the same Menu Designer as a MainMenu

Attach a context menu by setting the ContextMenu property of a control or the form


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Messagebox Function

1. MessageBox.Show(Arguments)

Several choices for argument list Introduces concept of Overloaded functions

Multiple signatures to choose from

MessageBox.Show(TextMessage)

MessageBox.Show(TextMessage, TitlebarText)

MessageBox.Show(TextMessage, TitlebarText, _MessageBoxButtons)

MessageBox.Show(TextMessage, TitlebarText, _MessageBoxButtons, MessageBoxIcon)


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Messagebox Function

MessageBox Icons and buttons Enumeration of constants


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Button Control

One of the most popular control in Visual Basic is the Button Control (previously Command Control). They are the controls which we click and release to perform some action. Buttons are used mostly for handling events in code, say, for sending data entered in the form to the database and so on. The default event of the Button is the Click event and the Button class is based on the ButtonBase class which is based on the Control class.


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Button Event

The default event of the Button is the Click event. When a Button is clicked it responds with the Click Event. The Click event of Button looks like this in code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As_System.EventArgs) Handles Button1.Click'You place the code here to perform action when Button is clickedEnd Sub


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Important Properties of Button1

Appearance BackColor and Background Image properties we can set a

background color and a background image to the button. We set the font color and font style for the text that appears on

button with ForeColor and the Font property. We change the appearance style of the button with the FlatStyle

property. We can change the text that appears on button with the Text

property with the TextAlign property we can set where on the button the

text should appear from a predefined set of options.


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Behavior Notable Behavior properties of the Button are the

Enabled and Visible properties. The Enabled property is set to True by default which

makes the button enabled and setting it's property to False makes the button Disabled.

With the Visible property we can make the Button Visible or Invisible. The default value is set to True and to make the button Invisible set it's property to False.


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Layout Layout properties are about the look of the Button. Note the

Dock property here. A control can be docked to one edge of its parent container or

can be docked to all edges and fill the parent container. The default value is set to none. If you want to dock the control towards the left, right, top, bottom and center you can do that by selecting from the button like image this property displays.

With the Location property you can change the location of the button.

With the Size property you can set the size of the button. Apart from the Dock property you can set it's size and location by moving and stretching the Button on the form itself.


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Creating a Button in Code Public Class Form1 Inherits System.Windows.Forms.Form

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e_As System.EventArgs) Handles_ MyBase.LoadDim Button1 as New Button()'declaring the button, Button1Button1.Text="Creating a Button"'setting the text to be displayed on the ButtonButton1.Location=New Point(100,50)'setting the location for the Button where it should be createdButton1.Size=New Size(75,23)'setting the size of the ButtonMe.Controls.Add(Button1)'adding the Button that is created to the form'the Me keyword is used to refer to the current object, in this case the FormEnd SubEnd Class


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Label

Labels are those controls that are used to display text in other parts of the application. They are based on the Control class.

Notable property of the label control is the text property which is used to set the text for the label.


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Creating a Label in Code

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)_Handles MyBase.Load Dim Label1 As New Label()Label1.Text = "Label"Label1.Location = New Point(135, 70)Label1.Size = New Size(30, 30)Me.Controls.Add(Label1)End Sub


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TextBox Control

Windows users should be familiar with textboxes. This control looks like a box and accepts input from the user.

The TextBox is based on the TextBoxBase class which is based on the Control class. TextBoxes are used to accept input from the user or used to display text.

By default we can enter up to 2048 characters in a TextBox but if the Multiline property is set to True we can enter up to 32KB of text. The image below displays a Textbox


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Some Notable Properties:

Behavior Enabled: Default value is True. To disable, set the

property to False. Multiline: Setting this property to True makes the

TextBox multiline which allows to accept multiple lines of text. Default value is False.

PasswordChar: Used to set the password character. The text displayed in the TextBox will be the character set by the user. Say, if you enter *, the text that is entered in the TextBox is displayed as *.ReadOnly: Makes this TextBox readonly. It doesn't allow to enter any text.

Visible: Default value is True. To hide it set the property to False


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Appearance section TextAlign: Allows to align the text from three

possible options. The default value is left and you can set the alignment of text to right or center.

Scrollbars: Allows to add a scrollbar to a Textbox. Very useful when the TextBox is multiline. You have four options with this property. Options are are None, Horizontal, Vertical and Both. Depending on the size of the TextBox anyone of those can be used.


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Code to Validate User Input

We can make sure that a TextBox can accept only characters or numbers which can restrict accidental operations. For example, adding two numbers of the form 27+2J cannot return anything. To avoid such kind of operations we use the KeyPress event of the TextBox.

Code that allows you to enter only double digits in a TextBox looks like this:

Private Sub TextBox1_KeyPress(ByVal sender As Object,ByVal e As_System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPressIf(e.KeyChar < "10" Or e.KeyChar > "100") ThenMessageBox.Show("Enter Double Digits")End IfEnd Sub


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Creating a TextBox in Code

Public Class Form1 Inherits System.Windows.Forms.FormPrivate Sub Form1_Load(ByVal sender As System.Object, ByVal e As_System.EventArgs) Handles MyBase.LoadDim TextBox1 as New TextBox()TextBox1.Text="Hello Mate"TextBox1.Location=New Point(100,50)TextBox1.Size=New Size(75,23)Me.Controls.Add(TextBox1)End SubEnd Class


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CheckBox

CheckBoxes are those controls which gives us an option to select, say, Yes/No or True/False. A checkbox is clicked to select and clicked again to deselect some option. When a checkbox is selected a check (a tick mark) appears indicating a selection. The CheckBox control is based on the TextBoxBase class which is based on the Control class. Below is the image of a Checkbox.


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Notable Properties

Important properties of the CheckBox in the Appearance section of the properties window are:

Appearance: Default value is Normal. Set the value to Button if you want the CheckBox to be displayed as a Button.BackgroundImage: Used to set a background image for the checkbox.CheckAlign: Used to set the alignment for the CheckBox from a predefined list.Checked: Default value is False, set it to True if you want the CheckBox to be displayed as checked.CheckState: Default value is Unchecked. Set it to True if you want a check to appear. When set to Indeterminate it displays a check in gray background.FlatStyle: Default value is Standard. Select the value from a predefined list to set the style of the checkbox.


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CheckBox

Important property in the Behavior section of the properties window is the ThreeState property which is set to False by default. Set it to True to specify if the Checkbox can allow three check states than two.


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CheckBox

Code to check a CheckBox's state Private Sub Button1_Click(ByVal sender As

System.Object, ByVal e As_System.EventArgs) Handles Button1.ClickIf CheckBox1.Checked = True ThenTextBox1.Text = "Checked"ElseTextBox1.Text = "UnChecked"End IfEnd Sub


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CheckBox

Creating a CheckBox in Code Private Sub Form1_Load(ByVal sender As

System.Object, ByVal e As_System.EventArgs) Handles_ MyBase.LoadDim CheckBox1 As New CheckBox()CheckBox1.Text = "Checkbox1"CheckBox1.Location = New Point(100, 50)CheckBox1.Size = New Size(95, 45)Me.Controls.Add(CheckBox1)End Sub


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ComboBox

ComboBox is a combination of a TextBox and a ListBox. The ComboBox displays an editing field (TextBox) combined with a ListBox allowing us to select from the list or to enter new text. ComboBox displays data in a drop-down style format. The ComboBox class is derived from the ListBox class. Below is the Image of a ComboBox.


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Notable properties of the ComboBox

The DropDownStyle property in the Appearance section of the properties window allows us to set the look of the ComboBox. The default value is set to DropDown which means that the ComboBox displays the Text set by it's Text property in the Textbox and displays it's items in the DropDownListBox below. Setting it to simple makes the ComboBox to be displayed with a TextBox and the list box which doesn't drop down. Setting it to DropDownList makes the ComboBox to make selection only from the drop down list and restricts you from entering any text in the textbox.

We can sort the ComboBox with it's Sorted property which is set to False by Default.

We can add items to the ComboBox with it's Items property.


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Removing items from a ComboBox You can remove all items or one particular

item from the list box part of the ComboxBox. Code to remove a particular item by it's Index number looks like this:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As_System.EventArgs) Handles Button1.ClickComboBox1.Items.RemoveAt(4)'removing an item by specifying it's indexEnd Sub


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Code to remove all items from the ComboBox Private Sub Button1_Click(ByVal sender As

System.Object, ByVal e As_System.EventArgs) Handles Button1.ClickComboBox1.Items.Clear()'using the clear method to clear the list boxEnd Sub


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ListBox

The ListBox control displays a list of items from which we can make a selection. We can select one or more than one of the items from the list. The ListBox control is based on the ListControl class which is based on the Control class. The image below displays a ListBox.


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Notable Properties of the ListBox In the Behavior Section HorizontalScrollbar: Displays a horizontal scrollbar to the

ListBox. Works when the ListBox has MultipleColumns.MultiColumn: The default value is set to False. Set it to True if you want the list box to display multiple columns.ScrollAlwaysVisible: Default value is set to False. Setting it to True will display both Vertical and Horizontal scrollbar always.SelectionMode: Default value is set to one. Select option None if you do not any item to be selected. Select it to MultiSimple if you want multiple items to be selected. Setting it to MultiExtended allows you to select multiple items with the help of Shift, Control and arrow keys on the keyboard.Sorted: Default value is set to False. Set it to True if you want the items displayed in the ListBox to be sorted by alphabetical order.


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Counting the number of Items in a ListBox Add a Button to the form and place the following code in it's click

event. Private Sub Button1_Click(ByVal sender As System.Object, ByVal e _

As System.EventArgs) Handles Button1.ClickTextBox1.Text = ListBox1.Items.Count'counting the number of items in the ListBox with the Items.CountEnd Sub When you run the code and click the Button it will display the number of items available in the ListBox.

Code to display the item selected from ListBox in a TextBox Private Sub ListBox1_SelectedIndexChanged(ByVal sender As

System.Object,_ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChangedTextBox1.Text = ListBox1.SelectedItem'using the selected item propertyEnd Sub When you run the code and click an item in the


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Code to remove a particular item Private Sub Button1_Click(ByVal sender As

System.Object, ByVal e _As System.EventArgs) Handles Button1.ClickListBox1.Items.RemoveAt(4)'removing an item by specifying it's indexEnd Sub Code to Remove all items

Private Sub Button1_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles Button1.ClickListBox1.Items.Clear()'using the clear method to clear the list boxEnd Sub


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Example


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Code to add and remove data

Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click

Dim STR As String STR = InputBox("ENTER DATA") ListBox1.Items.Add(STR)

End Sub--------------------------------------------------------------------------------Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click

ListBox1.Items.RemoveAt(ListBox1.SelectedIndex) End Sub


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Code to Shift single selected item from one listbox to another listbox

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click ListBox1.Items.Add(ListBox2.Items.Item(ListBox2.SelectedIndex)) ListBox2.Items.RemoveAt(ListBox2.SelectedIndex) End Sub


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Code to shift multiple items

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click Dim I As Integer

For Each I In ListBox2.SelectedIndices ListBox1.Items.Add(ListBox2.Items(I.ToString)) ListBox1.Items.RemoveAt(I) Next End Sub


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Example-checkbox and option button


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Private Sub CheckBox1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles CheckBox1.Click, CheckBox2.Click, CheckBox3.Click If flag = True Then If CheckBox1.Checked = True Then TextBox1.ForeColor = Color.Red ElseIf CheckBox2.Checked = True Then TextBox1.ForeColor = Color.Green ElseIf CheckBox3.Checked = True Then TextBox1.ForeColor = Color.Yellow End If Else If CheckBox1.Checked = True Then TextBox1.BackColor = Color.Red ElseIf CheckBox2.Checked = True Then TextBox1.BackColor = Color.Green ElseIf CheckBox3.Checked = True Then TextBox1.BackColor = Color.Yellow End If End If End Sub


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Example-Calculator


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Code for number buttons

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click, Button2.Click, Button3.Click, Button4.Click, Button5.Click, Button6.Click, Button7.Click, Button8.Click, Button15.Click, Button16.Click If flag = True Then TextBox1.Text += sender.text Else TextBox1.Text = "" flag = True End If End Sub


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Code for Operators buttons

Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click, Button10.Click, Button11.Click, Button12.Click op1 = CInt(TextBox1.Text) sign = sender.text TextBox1.Text = "" End Sub


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Code for equals buttons

Private Sub Button13_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button13.Click op2 = CInt(TextBox1.Text) Select Case sign Case "+" res = op1 + op2 Case "-" res = op1 - op2 Case "*" res = op1 * op2 Case "/" res = op1 / op2 End Select TextBox1.Text = res flag = False End Sub


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Handling Mouse Events in Forms We can handle mouse events such as mouse pointer movements in Forms. The mouse

events supported by VB .NET are as follows: MouseDown: This event happens when the mouse pointer is over the form/control and is

pressedMouseEnter: This event happens when the mouse pointer enters the form/controlMouseUp: This event happens when the mouse pointer is over the form/control and the mouse button is releasedMouseLeave: This event happens when the mouse pointer leaves the form/controlMouseMove: This event happens when the mouse pointer is moved over the form/controlMouseWheel: This event happens when the mouse wheel moves while the form/control has focusMouseHover: This event happens when the mouse pointer hovers over the form/control

The properties of the MouseEventArgs objects that can be passed to the mouse event handler are as follows:

Button: Specifies that the mouse button was pressedClicks: Specifies number of times the mouse button is pressed and releasedX: The X-coordinate of the mouse clickY: The Y-coordinate of the mouse clickDelta: Specifies a count of the number of detents (rotation of mouse wheel) the mouse wheel has rotated


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Common Dialogs

Visual Basic .NET comes with built-in dialog boxes which allow us to create our own File Open, File Save, Font, Color dialogs much like what we see in all other windows applications. To make a dialog box visible at run time we use the dialog box's ShowDialog method. The Dialog Boxes which come with Visual Basic .NET are: OpenFileDialog, SaveFileDialog FontDialog ColorDialog PrintDialog PrintPreviewDialog and PageSetupDialog. We will be working with OpenFile, SaveFile, Font and Color Dialog's in this section. The return values of all the above said dialog boxes which will determine which selection a user makes are: Abort, Cancel, Ignore, No, None, OK, Return, Retry and Yes.


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OpenFileDialog

Properties of the OpenFileDialog are as follows: AddExtension: Gets/Sets if the dialog box adds extension to file names if the user doesn't supply the extension.CheckFileEixsts: Checks whether the specified file exists before returning from the dialog. CheckPathExists: Checks whether the specified path exists before returning from the dialog. DefaultExt: Allows you to set the default file extension.FileName: Gets/Sets file name selected in the file dialog box.FileNames: Gets the file names of all selected files.Filter: Gets/Sets the current file name filter string, which sets the choices that appear in the "Files of Type" box.FilterIndex: Gets/Sets the index of the filter selected in the file dialog box.InitialDirectory: This property allows to set the initial directory which should open when you use the OpenFileDialog.


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MultiSelect: This property when set to True allows to select multiple file extensions.ReadOnlyChecked: Gets/Sets whether the read-only checkbox is checked.RestoreDirectory: If True, this property restores the original directory before closing.ShowHelp: Gets/Sets whether the help button should be displayed. ShowReadOnly: Gets/Sets whether the dialog displays a read-only check box.Title: This property allows to set a title for the file dialog box. ValidateNames: This property is used to specify whether the dialog box accepts only valid file names.


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SaveFileDialog

Save File Dialog's are supported by the SaveFileDialog class and they allow us to save the file in a specified location.

Properties of the Save File Dialog are the same as that of the Open File Dialog. Please refer above. Notable property of Save File dialog is the OverwritePromopt property which displays a warning if we choose to save to a name that already exists.


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FontDialog

Properties of the FontDialog are as follows: AllowSimulations: Gets/Sets whether the dialog box allows graphics device interface font simulations.Color: Gets/Sets selected font color.Font: Gets/Sets the selected font.FontMustExist: Gets/Sets whether the dialog box specifies an error condition if the user attempts to select a font or size that doesn't exist.MaxSize: Gets/Sets the maximum point size the user can select.MinSize: Gets/Sets the mainimum point size the user can select.ShowApply: Gets/Sets whether the dialog box contains an apply button.ShowColors: Gets/Sets whether the dialog box displays the color choice.ShowEffects: Gets/Sets whether the dialog box contains controls that allow the user to specify to specify strikethrough, underline and text color options.ShowHelp: Gets/Sets whether the dialog box displays a help button.


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ColorDialogs

Properties of ColorDialog are as follows:

AllowFullOpen: Gets/Sets whether the user can use the dialog box to define custom colors.AnyColor: Gets/Sets whether the dialog box displays all the available colors in the set of basic colons.Color: Gets/Sets the color selected by the user.CustomColors: Gets/Sets the set of custom colors shown in the dialog box.FullOpen: Gets/Sets whether the controls used to create custom colors are visible when the dialog box is opened.ShowHelp: Gets/Sets whether the dialog box displays a help button.SolidColorOnly: Gets/Sets whether the dialog box will restrict users to selecting solid colors only.


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TREEVIEW CONTROL

The Windows Forms TreeView control displays a hierarchy of nodes, like the way files and folders are displayed in the left pane of Windows Explorer. Each node might contain other nodes, called child nodes. Parent nodes, or nodes that contain child nodes, can be displayed as expanded or collapsed. A tree view can also be displayed with check boxes next to the nodes, if the tree view's CheckBoxes property is set to true. You can then programmatically select or clear nodes by setting the node's Checked property to true or false.


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TREEVIEW PROPERTIES

1. NODES-contains the list of top-level nodes in the tree view

2. SELECTEDNODES-sets the currently selected node

3. ImageList -Icons can be displayed next to the nodes; the images are taken from the ImageList control


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TREEVIEW-ADDING NODES

To add or remove nodes in the designer

1. Select the TreeView control or add one to the form.

2. In the Properties window, click the ellipsis () button next to the Nodes property.

3. The TreeNode Editor appears.

4. To add nodes, a root node must exist; if one does not exist, you must first add a root by clicking the Add Root button. You can then add child nodes by selecting the root or any other node and clicking the Add Child button. To delete nodes, select the node to delete and then click the Delete button.


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To add nodes programmatically

Use the Add method of the tree view's Nodes property.

Dim newNode As TreeNode = New TreeNode("Text for new node")

TreeView1.SelectedNode.Nodes.Add(newNode)


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To remove nodes programmatically

Use the Remove method of the tree view's Nodes property to remove a single node, or the Clear method to clear all nodes.

TreeView1.Nodes.Remove(TreeView1.SelectedNode)

nodes.TreeView1.Nodes.Clear()


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Listview Control

The Windows Forms ListView control displays a list of items with icons. You can use a list view to create a user interface like the right pane of Windows Explorer

The control has four view modes: LargeIcon, SmallIcon, List, and Details. The LargeIcon mode displays large icons next to the item text; the items appear in multiple columns if the control is large enough. The SmallIcon mode is the same except that it displays small icons. The List mode displays small icons but is always in a single column. The Details mode displays items in multiple columns.


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The key property of the ListView control is Items, which contains the items displayed by the control. The SelectedItems property contains a collection of the items currently selected in the control. The user can select multiple items, for example to drag and drop several items at a time to another control, if the MultiSelect property is set to true. The ListView control can display check boxes next to the items, if the CheckBoxes property is set to true.

The Activation property determines what type of action the user must take to activate an item in the list: the options are Standard, OneClick, and TwoClick. OneClick activation requires a single click to activate the item. TwoClick activation requires the user to double-click to activate the item; a single click changes the color of the item text. Standard activation requires the user to double-click to activate an item, but the item does not change appearance


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To add or remove items in the designer

In the Properties window, click the ellipsis button () next to the Items property.

The ListViewItem Collection Editor appears.

To add an item, click the Add button. You can then set properties of the new item, such as the Text and ImageIndex properties. To remove an item, select it and click the Remove button.


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To add items programmatically

Use the Add method of the Items property.

ListView1.Items.Add("List item text", 3)


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To add columns in the designer Set the control's View property to Details. In the Properties window, click the ellipsis

button () next to the Columns property. The ColumnHeader Collection Editor

appears. Use the Add button to add new columns. You

can then select the column header and set its text (the caption of the column), text alignment, and width.


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To add columns programmatically

Set the control's View property to Details.

Use the Add method of the list view's Columns property.

' Visual Basic' Set to details viewListView1.View = View.Details' Add a column with width 20 and left alignmentListView1.Columns.Add("File type", 20, HorizontalAlignment.Left)


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Framework basics

CLR CLI CTS MANAGED CODE ASSEMBLY IL


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CLR(Common language Runtime)

Full form of CLR is common language runtime and it forms the heart of the .net framework.all languages have runtime and it’s the responsibility of the runtime to take care of the code execution of the program.


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Common Language Infrastructure (CLI) At the heart of the .NET Framework is a new

mechanism for loading and running programs and managing their interactions. This mechanism is described in the Common Language Infrastructure (CLI)

The CLI is just a specification—it has to be implemented in order to be useful. An implementation of the CLI is known as a Common Language Runtime (CLR). Microsoft's CLR implementation on the Windows platform is not under ECMA's control, but it is Microsoft's intention that the CLR be a fully compliant implementation of the CLI.


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Common Type System (CTS)

In order that two language communicate smoothly CLR has CTS .Example in VB you have integer and in c++ you have long these data types are not compatible so the interfacing between the m is very complicated. in order that two different languages can communicate Microsoft introduced common type system. so integer data type in vb6 and int data type in c++ will convert it to system .ini.int32 which is data type of CTS .CLS is subset of CTS.


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Common Language Specification (CLS) This is a subset of the CTS which all .NET

languages are expected to support.it was always a dream of Microsoft ot unite all different languages in to one umnrella and CLS is one step towards that .microsoft has defined CLS which is nothing but guidelines that language has to follow so that it can communicate with other .NET languages in a seamlesls manner


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Managed code

Managed code runs inside the environment of CLR that is within .net runtime.in short all IL are managed code.but if you are using some third party software example vb6 or vc++ component they are unmanaged code as .net runtime does not have control over the source code execution of the language.


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Memory Management and Garbage Collection In any object-oriented programming

environment, there arises the need to instantiate and destroy

objects. Instantiated objects occupy memory. When objects are no longer in use, the memory they occupy should be reclaimed for use by other objects


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Assembly

Assembly is unit of deployment like exe of dll

an assemble consists of one or more files and represents a group of resource type definitions and implementations of those types.an assembnly group of resources type definations and implementation of those types.an assembly may also contain references to other assaemblies .

the manifest is part of the assembly thus making the assembly self describing


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Intermediate Language (IL) and Just-In-Time (JIT) Compilation

All compilers that target the CLR compile source code to Intermediate Language (IL), also known as Common Intermediate Language (CIL).

IL is a machine language that is not tied to any specific machine. Microsoft designed it from scratch to support the CLI's programming concepts.

The CLI specifies that all CLR implementations can compile or interpret IL on the machine on which the CLR is running.

If the IL is compiled (versus interpreted), compilation can occur at either of two times:

Immediately prior to a method in the application being executed

At deployment time


120

Contd…

. The compiled code is not saved to disk, so if the application is stopped and restarted, the compilation must occur again. This is known as just-in-time (JIT) compilation and is the most common scenario.

In the second case, the application is compiled in its entirety at deployment time. IL is saved to .exe and .dll files. When such a file containing IL is executed, the CLR knows how to invoke the JIT compiler and execute the resulting code. Note that on the Microsoft Windows platforms, IL is always compiled—never interpreted.


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OOP-Concept

Objects

Visual basic allows you to create object by defining class.Class may have properties and methods.Object is a thing which is properties and methods.

User defined class can be created in vb.and that classes can be incorporated to projects as a references.

Properties are the characteristic and methods are the operation that can be performed on an object.


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OOP-Terminology

Encapsulation Inheritance Polymorphism


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CLASSES

Instantiating an object

New class name

i.E

Dim c = new font(“arial”,12)

Lblfnt.font=c


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Creating your own classes Create a new application of type class library Create properties of the class. Property procedure

the way that your class allows its properties is to be accessed is through a property procedure. it may contain a get to retrieve a property value and a set to assign a value to the property.

Following is the example:Property op1() As Integer Get op1 = no1 End Get Set(ByVal Value As Integer) no1 = Value End Set End Property


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Creating new object using classes

Create new object using following statement in windows application

Dim c as new class name

This class name must be add as a reference in a project.


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ERROR HANDLING

Error messages can occur while an application is running, either within the Visual Basic .NET environment or as a stand-alone executable. Some of these can also occur during design time or compile time

Visual Basic compiler errors occur when the compiler encounters problems in the code. The code causing the errors is marked with a wavy line underneath it in the Code Editor, and when your mouse pauses over the marked code, the error message appears. The messages also appear in the Task List.

Visual Basic run-time errors occur when an application attempts to perform an action that the system cannot execute.


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ERROR HANDLING-Types of Errors

In Visual Basic, errors (also called exceptions) fall into one of three categories: syntax errors, run-time errors, and logic errors.

Syntax ErrorsSyntax errors are those that appear while you write your code.

Visual Basic checks your code as you type and alerts you if you make a mistake, such as misspelling a word or using a language element improperly. Syntax errors are the most common type of errors. You can fix them easily in the coding environment as soon as they occur.

Note The Option Explicit statement is one means of avoiding syntax errors. It forces the programmer to declare, in advance, all the variables to be used in the application. Therefore, when those variables are used in the code, any typographic errors are caught immediately and can be fixed.


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Run-Time ErrorsRun-time errors are those that appear only after you compile and

run your code. These involve code that may appear to be correct in that it has no syntax errors, but that will not execute. For example, you might correctly write a line of code to open a file. But if the file is corrupted, the application cannot carry out the Open function, and it stops running. You can fix most run-time errors by rewriting the faulty code, and then recompiling and rerunning it.

Logic ErrorsLogic errors are those that appear once the application is in use.

They most often take the form of unwanted or unexpected results in response to user actions. For example, a mistyped key or other outside influence might cause your application to stop working within expected parameters, or altogether. Logic errors are generally the hardest type to fix, since it is not always clear where they originate.


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EXCEPTION

Visual Basic supports both structured and unstructured exception (error) handling. By placing specific code in your application, you can handle most of the errors users may encounter and enable the application to continue running. Structured and unstructured error handling allow you to plan for potential errors, preventing them from interfering with the intended purpose of the application.


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Consider using exception handling in any method that uses operators that may generate an exception, or that calls into or accesses other procedures that may generate an exception.

If an exception occurs in a method that is not equipped to handle it, the exception is propagated back to the calling method , or the previous method. If the previous method also has no exception handler, the exception is propagated back to that method 's caller, and so on. The search for a handler continues up the call stack, which is the series of procedures called within the application. If it fails to find a handler for the exception, an error message is displayed and the application is terminated.


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EXCEPTION

Structured Exception HandlingIn structured exception handling, blocks of code are encapsulated, with

each block having one or more associated handlers. Each handler specifies some form of filter condition on the type of exception it handles. When an exception is raised by code in a protected block, the set of corresponding handlers is searched in order, and the first one with a matching filter condition is executed. A single method can have multiple structured exception handling blocks, and the blocks can also be nested within each other.

The Try...Catch...Finally statement is used specifically for structured exception handling. For more information

Unstructured Exception HandlingThe On Error statement is used specifically for unstructured exception

handling. In unstructured exception handling, On Error is placed at the beginning of a block of code. It then has "scope" over that block; it handles any errors occurring within the block. If the program encounters another On Error statement, that statement becomes valid and the first statement becomes


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Structured Exception Handling

Visual Basic supports structured exception handling, which helps you create and maintain programs with robust, comprehensive error handlers. Structured exception handling is code designed to detect and respond to errors during execution by combining a control structure (similar to Select Case or While) with exceptions, protected blocks of code, and filters.

Using the Try...Catch...Finally statement, you can protect blocks of code that have the potential to raise errors. You can nest exception handlers, and the variables declared in each block will have local scope.


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TRY..CATCH STATEMENTTry [ tryStatements ][ Catch [ exception [ As type ] ] [ When expression ] [ catchStatements ] ][ Exit Try ]...[ Finally [ finallyStatements ] ]End Try PartstryStatements Optional. Statement(s) where an error can occur. Can be a compound statement. Catch Optional. Multiple Catch blocks permitted. If an exception occurs while processing the Try

block, each Catch statement is examined in textual order to determine if it handles the exception. Exception represents the exception that has been thrown.

exception Optional. Any variable name. The initial value of exception is the value of the thrown error. Used

with Catch to specify the error caught. type Optional. Specifies the type of class filter. If the value of exception is of the type specified by

type or of a derived type, the identifier becomes bound to the exception object. When Optional. A Catch statement with a When clause will only catch exceptions when expression

evaluates to True. A When clause is only applied after checking the type of the exception, and expression may refer to the identifier representing the exception.


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expression Optional. Must be implicitly convertible to Boolean. Any expression that describes a

generic filter. Typically used to filter by error number. Used with When keyword to specify circumstances under which the error is caught.

catchStatements Optional. Statement(s) to handle errors occurring in the associated Try block. Can

be a compound statement. Exit Try Optional. Keyword that breaks out of the Try...Catch...Finally structure. Execution

resumes with the Finally block if present, otherwise with the code immediately following the End Try statement. Not allowed in Finally blocks.

Finally Optional. A Finally block is always executed when execution leaves any part of the

Try statement. finallyStatements Optional. Statement(s) that are executed after all other error processing has

occurred. End Try Terminates the Try...Catch...Finally structure.


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EXAMPLE


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Data Access Technologies

Most applications require some form of data access. If you are creating a new application, you have three excellent data access choices:

ADO.NET ADO OLE DB. If you need to modify the data access for an existing application,

you might continue using the application's current data access technology for maintenance convenience. However, if you expect the application to have a long lifecycle, you should consider reengineering to use either ADO.NET for managed applications or ADO for native applications. In the long run, the newer data access technologies typically reduce development time, simplify code, and provide excellent performance.


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ADO.NET

ADO.NET is the strategic application-level interface for providing data access services in the Microsoft .NET Platform. You can use ADO.NET to access data sources using the new .NET Framework data providers. These data providers include:

.NET Framework Data Provider for SQL Server. .NET Framework Data Provider for OLE DB. .NET Framework Data Provider for ODBC. .NET Framework Data Provider for Oracle. These data providers support a variety of development

needs, including middle-tier business objects using live connections to data in relational databases and other stores.


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ADO

For applications written in native code, ADO provides a COM-based application-level interface for OLE DB data providers. Similar to ADO.NET, ADO supports a variety of development needs, including the creation of front-end database clients and middle-tier business objects using live connections to data in relational databases and other stores. And, like ADO.NET, ADO can construct client-side recordsets, use loosely coupled recordsets, and handle OLE DB's data shaping rowsets.


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OLE DB

OLE DB is the strategic system-level programming interface for accessing data, and is the underlying technology for ADO as well as a source of data for ADO.NET. OLE DB is an open standard for accessing all kinds of data — both relational and non-relational data including: mainframe ISAM/VSAM and hierarchical databases; e-mail and file system stores; text, graphical, and geographical data; and custom business objects.

OLE DB provides consistent, high-performance access to data and supports a variety of development needs, including the creation of front-end database clients and middle-tier business objects using live connections to data in relational databases and other stores.


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ADO.NET Data Components

Data adapter Data Reader Command Data connection


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Introduction to ADO.NET Connection Design Tools To move data between a data store and your application, you must first

have a connection to the data store. Data adapters, data connections, data commands, and data readers are

the components that make up a .NET Framework data provider. Microsoft and third-party providers can make available other .NET

Framework data providers that can be integrated into Visual Studio. In ADO.NET you create and manage connections using connection

objects: SqlConnection - an object that manages a connection to a SQL Server

version 7.0 or later. It is optimized for use with SQL Server 7.0 or later by (among other things) bypassing the OLE DB layer.

OleDbConnection - an object that manages a connection to any data store accessible via OLE DB.

OdbcConnection - an object that manages a connection to a data source created by using a connection string or ODBC data source name (DSN).

OracleConnection - an object that manages a connection to Oracle databases.


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Opening and Closing Connections

The two primary methods for connections are Open and Close. The Open method uses the information in the ConnectionString property to contact the data source and establish an open connection. The Close method shuts the connection down. Closing connections is essential, because most data sources support only a limited number of open connections, and open connections take up valuable system resources.

If you are working with data adapters or data commands, you do not have to explicitly open and close a connection. When you call a method of these objects (for example, the data adapter's Fill or Update method), the method checks whether the connection is already open. If not, the adapter opens the connection, performs its logic, and closes the connection again.

Methods such as Fill only open and close the connection automatically if it is not already open. If the connection is open, the methods use it but do not close it. This gives you the flexibility to open and close data commands yourself. You might do this if you have multiple data adapters that share a connection. In that case, it is inefficient to have each adapter open and close the connection when you call its Fill method. Instead, you can open the connection, call the Fill method of each adapter, and then close the connection when you are done.


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CODE TO ADD NEW RECORD

Me.BindingContext(DataSet11, "studentmarks").EndCurrentEdit()

Me.BindingContext(DataSet11, "studentmarks").AddNew()

Dim Changes As WindowsApplication12.DataSet1 = New WindowsApplication12.DataSet1

Me.BindingContext(DataSet11, "studentmarks").EndCurrentEdit()

Changes = CType(DataSet11.GetChanges,WindowsApplication12.DataSet1)

Me.OleDbConnection1.Open()

OleDbDataAdapter1.Update(DataSet11)

Me.OleDbConnection1.Close()

DataSet11.Merge(Changes)

DataSet11.AcceptChanges()


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CODE TO DELETE RECORD

Me.BindingContext(DataSet11, "studentmarks").RemoveAt(Me.BindingContext(DataSet11, "studentmarks").Position)


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ARRAY


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ARRAYLIST COLLECTION

An ArrayList is a sophisticated version of an array.

The ArrayList class provides some features that are offered in most Collections classes but are not in the Array class.


148

Contd…

The capacity of an Array is fixed, whereas the capacity of an ArrayList is automatically expanded as required.

If the value of the ArrayList.Capacity property is changed, the memory reallocation and copying of elements are automatically done.


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Contd…

ArrayList provides methods that add, insert, or remove a range of elements. In Array, you can get or set the value of only one element at a time.

A synchronized version of ArrayList is easy to create using the Synchronized method. Array leaves it up to the user to implement synchronization.


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Contd…

ArrayList provides methods that return read-only and fixed-size wrappers to the collection. Array does not.


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CONTD…

On the other hand, Array offers some flexibility that ArrayList does not. For example:

You can set the lower bound of an Array, but the lower bound of an ArrayList is always zero.


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Contd..

An Array can have multiple dimensions, while an ArrayList always has exactly one dimension.

An Array of a specific type (other than Object) has better performance than an ArrayList because the elements of ArrayList are of type Object and, therefore, boxing and unboxing typically occur if storing or retrieving a value type.


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Contd…

Array is in the System namespace; ArrayList is in the System.Collections namespace.


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Properties

Capacity count Isreadonly


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Methods

Add Addrange Binarysearch Clear Copyto Equals Insert Insertrange Remove Reverse


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HASHTABLE COLLECTION

A Hashtable consists of buckets that contain the elements of the collection. A bucket is a virtual subgroup of elements within the Hashtable, which makes searching and retrieving easier and faster than in most collections. Each bucket is associated with a hash code, generated using a hash function and based on the key of the element.


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Contd…

When an object is added to a Hashtable, it is stored in the bucket that is associated with the hash code that matches the object's hash code. When a value is being searched for in the Hashtable, the hash code is generated for that value, and the bucket associated with that hash code is searched.


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CONTD…

Properties Count Keys Item values

Methods Add Remove Contains clear


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SortedList Class

The SortedList class is like a hybrid between Hashtable and ArrayList.

As with Hashtable, SortedList is based on the IDictionary interface; therefore, each element of a SortedList is a key-and-value pair. SortedList provides methods that return only the list of keys or only the list of values.

As with ArrayList, a SortedList is a sequence of elements. It is indexed, and is sorted according to a specified comparer.

SortedList is unique among all Collections classes in that each element can be accessed three ways: using the key, the value, or the index.


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Contd…

Properties Capacity Count Items keys

Methods Add Clear contains


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Char class

Char variables are stored as unsigned 16-bit (2-byte) numbers ranging in value from 0 through 65535. Each number represents a single Unicode character. Direct conversions between the Char data type and the numeric types are not possible, but you can use the AscW and ChrW functions for this purpose.


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Contd…

Properties Maxvalue Minvalue

Methods Campareto Isdigit Isletter Equals


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String class

Represents a set of unicode characters Properties

Chars Length


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Methods Compare Compareto Concate Copy Copyto Equals Indexof Insert


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Join Lastindexof Remove Replace Split Substring Toupper tolower


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StringBuilder Class

The String object is immutable. Every time you use one of the methods in the System.String class, you create a new string object in memory, which requires a new allocation of space for that new object. In situations where you need to perform repeated modifications to a string, the overhead associated with creating a new String object can be costly. The System.Text.StringBuilder class can be used when you want to modify a string without creating a new object. For example, using the StringBuilder class can boost performance when concatenating many strings together in a loop.


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Contd…

Properties Capacity Chars Length

Methods Append Remove Insert Replace Tostring


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DATETIME

Represents an instant in time, typically expressed as a date and time of day.

Properties Date Dayofweek Dayofyear Hour Minute Month Now Timeofday Today year


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Contd…

Methods Add Addmonth addday


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Vb.net Notes

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