VB.Net Introduction

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VB.Net Introduction

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VB.Net Introduction. Visual Studio 2010 Demo. Start page: New project/ Open project/ Recent projects Starting project: File/New Project/ Windows Website File/New website Project name Project windows: Form design view/Form code view Solution Explorer Server Explorer Property Window - PowerPoint PPT Presentation

Transcript of VB.Net Introduction

Page 1: VB.Net Introduction

VB.Net Introduction

Page 2: VB.Net Introduction

Visual Studio 2010 Demo• Start page: New project/ Open project/Recent projects• Starting project:

• File/New Project/– Windows– Website

• File/New website• Project name

• Project windows:– Form design view/Form code view– Solution Explorer– Server Explorer– Property Window– ToolBox– Project/Add New Item– Project properties: Right-click project name and choose Properties

• Start Up form– Property window example

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Introduction to Visual Basic .Net

• Event-driven programming– The interface for a VB program consists of one

or more forms, containing one or more controls (screen objects).

– Form and controls have events that can respond to. Typical events include clicking a mouse button, type a character on the keyboard, changing a value, etc.

– Event procedure

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Form

• Properties:– Name, FormBorderStyle, Text, BackColor,

BackImage, Opacity

• Events:– Load, FormClosing, FormClosed– GotFocus, LostFocus– MouseHover, Click, DoubleCLick

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Typical VB.Net Controls

• TextBox• Label• Button• CheckBox• RadioButton• ListBox• ComboBox• PictureBox

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Text Box• Properties:

– AutoSize, BorderStyle, CauseValidation, Enabled, Locked, Multiline, PasswordChar, ReadOnly, ScrollBar, TabIndex, Text, Visible, WordWrap, etc.

• Properties can be set at the design time or at the run time using code.

• To refer to a property: – ControlName.PropertyName– Ex. TextBox1.Text– Note: The Text property is a string data type and

automatically inherits the properties and methods of the string data type.

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Typical VB.Net Programming Tasks

• Creating the GUI elements that make up the application’s user interface.– Visualize the application.– Make a list of the controls needed.

• Setting the properties of the GUI elements

• Writing procedures that respond to events and perform other operations.

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Demo

Num1

Num2

Sum =

.Control properties

.Event: Click, MouseMove, Form Load, etc.

.Event proceduresSum: textBox3.text=CStr(CDbl(textBox1.text)+CDbl(textBox2.text))Or (CDbl(textBox1.text)+CDbl(textBox2.text)).toString

.Demo: Text alignment (TextAlign property)

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Using VB Functions or .Net Methods?

• VB functions: Cstr, Cdbl, …

• .Net framework:– System.Convert

• TextBox3.Text = (System.Convert.ToDouble(TextBox1.Text) + System.Convert.ToDouble(TextBox2.Text)).ToString

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Creating a C# Project

• VB functions such as Cstr, Cdbl, … are not available

• .Net framework is the same

• textBox3.Text = (System.Convert.ToDouble(textBox1.Text) * 2).ToString(); Note: ToString with ()

• With C# , control/variable names are case sensitive.

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VB Projects

• A VB project consists of several files. Visual Studio .Net automatically creates a project folder to keep all project files in the folder.– Project file

– Form file

– Modules

– Class file

– Etc.

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Configure VB Project

• Project property page– Application– Compile– References

• Tools/Options– Environment

– Projects and Solutions

» VB defaults

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VB Defaults

• Option Explicit: – On --- must declare variables before use

• Option Strict:– Off --- VB will convert the data

• Option Compare:– Binary --- case sensitive– Text --- case insensitive

• Option Infer– On --- When you set Option Infer to On, you can declare variables

without explicitly stating a data type. The compiler infers the data type of a variable from the type of its initialization expression.

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Example of Option Infer

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Variable Declarations• Option Explicit• Dim variableName as DataType• Variable naming rules:

– The first character must be a letter or an underscore character.

– Use only letters, digits, and underscore.– Cannot contain spaces or periods.– No VB keywords

• Naming conventions:– Descriptive– Consistent lower and upper case characters.

• Ex. Camel casing: lowerUpper, employeeName

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Control Naming Conventions

• The first three letters should be a lowercase prefix that indicates the control’s type.– frm, txt, lbl, btn.

• The first letter after the prefix should be uppercase.– txtSalary, lblMessage

• The part of the control name after the prefix should describe the control’s purpose in the application.

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VB Data Types

• Boolean (True/False): 2 bytes• Byte: Holds a whole number from 0 to 255.• Char: single character• Date: date and time, 8 bytes.• Decimal: Real number up to 29 significant digits, 16 bytes• Double: real, 8 bytes• Single: real, 4 bytes• Integer: 4 bytes (int32, uint32)• Long: 8 bytes integer• Short: 2 bytes integer• String• Object: Holds a reference of an object

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Variable Declaration Examples

• Dim empName as String

• Declare multiple variables with one Dim:– Dim empName, dependentName, empSSN as String

• Dim X As Integer, Y As Single

• Initiatialization– Dim interestRate as Double = 0.0715

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Variable Default Value

• Variables with a numeric data type: 0

• Boolean variables: False

• Date variables: 12:00:00 AM, January 1 of the year 1.

• String variables: Nothing

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Variable Scope• Block-level scope: declared within a block of code

terminated by an end, loop or next statement.– If city = “Rome” then

• Dim message as string = “the city is in Italy”

• MessageBox.Show(message)

– End if

• Procedural-level scope: declared in a procedure• Class-level, module-level scope: declared in a

class or module but outside any procedure with either Dim or Private keyword.

• Project-level scope: a module variable declared with the Public keyword.

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Data Conversion• Implicit conversion: When you assign a value of

one data type to a variable of another data type, VB attempts to convert the value being assigned to the data type of the variable if the OptionStrict is set to Off.

• Explicit conversion:– VB.Net Functions: CStr, Ccur, CDbl, Cint, CLng,

CSng, Cdate,Val, etc.– .Net System.Convert

• Type class’s methods:– toString

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Date Data Type

• Variables of the Date data type can hold both a date and a time. The smallest value is midnight (00:00:00) of Jan 1 of the year 1. The largest value is 11:59:59 PM of Dec. 31 of the year 9999.

• Date literals: A date literal may contain the date, the time, or both, and must be enclosed in # symbols:– #1/30/2003#, #1/31/2003 2:10:00 PM#– #6:30 PM#, #18:30:00#

• Note: ControlPanel/RegionalOptions/Date

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• Date Literal Example:– Dim startDate as dateTime– startDate = #1/30/2003#

• Use the System.Convert.ToDateTime function to convert a string to a date value:– startDate = System.Convert.ToDateTime(“1/30/2003”)– If date string is entered in a text box:

• startDate = System.Convert.ToDateTime(txtDate.text)• Or startDate=Cdate(txtDate.text)

• Date data type format methods

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Some Date Functions

• Now: Current date and time• Today: Current date• TimeOfDay• DateDiff:• Demo

– Days between two dates– Days to Christmas

• DateDiff(DateInterval.Day, Today(), #12/25/2007#)

– Date data type properties and methods

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Using Online HelpExample:Search Help for DateDiff

• MSDN VB Developer Center– http://msdn.microsoft.com/en-us/vbasic/

default.aspx– Library/Visual Studio/Visual Studio

Languages/Visual Basic• Reference 

– Language reference

» Functions:

» DateDiff Function

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Arithmetic and String Operators

• +, -, *, /. \, ^

• String Concatenation: &, +

• Compound operator:: X= X+1 or X +=1

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IF Statement

• IF condition THEN

statements

[ELSEIF condition-n THEN

[elseifstatements]

[ELSE

[elsestatements]]]

End If

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Select Case Structure

• SELECT CASE testexpression

[CASE expressionlist-n

[Statements]

[CASE ELSE

[elsestatements]

END SELECT

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Select Case Example• SELECT CASE temperature

CASE <40Text1.text=“cold”

CASE < 60Text1.text=“cool”

CASE 60 to 80Text1.text=“warm”

CASE ELSEText1.text=“Hot”

End Select

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Loop

• FOR index – start TO end [STEP step]

[statements]

[EXIT FOR]

NEXT index

DO [{WHILE| UNTIL} condition]

[statements]

[EXIT DO]

LOOP

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Do While/Do UntilPrivate Sub Command1_Click()Dim counter As Integercounter = 0Do While counter <= 5 Debug.write(counter) counter = counter + 1LoopText1.Text = counterEnd Sub

Private Sub Command2_Click()Dim counter As Integercounter = 0Do Until counter > 5 Debug.write(counter) counter = counter + 1LoopText1.Text = counterEnd Sub

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With … End With

With TextBox1

.Height = 250

.Width = 600

.Text = “Hello”

End With

Convenient shorthand to execute a series of statements on a single object. Within the block, the reference to the object is implicit and need not be written.

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Procedures

. Sub procedure:

Sub SubName(Arguments)

End Sub– To call a sub procedure SUB1

• CALL SUB1(Argument1, Argument2, …)

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Function

• Private Function tax(salary) As Double

• tax = salary * 0.1

• End Function

– Or• Private Function tax(salary)

• Return salary * 0.1

• End Function

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Call by Reference Call by Value

• ByRef– The address of the item is passed. Any changes

made to the passing variable are made to the variable itself.

• ByVal– Default– Only the variable’s value is passed.

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ByRef, ByVal example

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim myStr As String

myStr = TextBox1.Text

Call ChangeTextRef (myStr)

TextBox1.Text = myStr

End Sub

Private Sub ChangeTextRef(ByRef strInput As String)

strInput = "New Text"

End Sub