VB.net Basicss

8/2/2019 VB.net Basicss

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Why should we implementthis new software developerstool?

What language will be THEmost used language?

Is this simply anotherupgrade?

What classes couldincorporate the content of.NET?


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Easier to UseModernizedMore Powerful than VB 6.0

Higher level of access to systemresources that in the past required theuse of languages like C++

True Object InheritanceGarbage Collection for better memory

management


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NO!VB.NET omits quite a few forms of

syntax

VB.NET requires a total rewrite ratherthan a simple port of code

VB.NET is not dependent on older

libraries such as VBA runtime and ADO(ActiveX Database Object)


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The forms engine has been replaced bythe forms engine built into .NET

This new forms engine is called

Windows Forms (or Win Forms forshort)

Win Forms add such features as docking

and opacity


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In VB6, forms wereclasses, but you rarelytreated them that way

VB .NET shows the codethat instantiates the form

To show additional forms,you must first instantiatethem


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C# is a new language thatwas designed to be friendlyto programmers who arealready proficient in C or

C++ Either language can be used

to write software that takesfull advantage of the CLRand .NET framework


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Collapsed Regions

Collapsed

Region

Collapsed

Procedure

Class

List

Method ListTabs


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There have been a number of changes in VB.NET. General changes include: Form changes

Option Strict

Event Handler changes

Default Properties

Calling Subs and Functions

Boolean operators

Using CTRL + Space to finish variables


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In VB6, forms were classes, but you rarelytreated them that way

VB .NET shows the code that instantiatesthe form

To show additional forms, you must firstinstantiate them


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The And and Or keywords do not short-circuit in

VB and VB .NET Both sides of an operator are evaluated, even if the first

option invalidates the statementVB .NET adds two short-circuiting Boolean

operators: AndAlso

OrElse


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Dim x As Integer

x = 0

If x>2 And 5\x > 1 Then ...

This If statement is already false on thex>2 part, but 5\x is still checked becauseAnd does not short-circuit

In this case, 5\xcauses a divide by zero

error


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Dim x As Integer

x = 0

If x>2 AndAlso 5\x > 1 Then ...

This If statement is already false on thex>2 part, so the AndAlso does not checkthe 5\x portion

The key result: No Error!


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Firstly the Currency data type is no longerused in VB 6.0 Currency has been replaced with Decimal in

VB.NET

The Currency data type (64 bit) does notprovide sufficient accuracy to avoid roundingerrors, so Decimal (96 bit) was created as itsown data type.

Dim x As Currencyis upgraded to:Dim x As Decimal


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VB 6.0 - Long variables were stored as 32-bit numbers and Integer variables as 16-bitnumbers

VB.NET - Long variables are stored as 64-bit numbers, Integer variables are storedas 32-bit numbers, and Short variables arestored as 16-bit numbers.


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Variant data types are changed to Object due

to keeping all the languages more similar.

This is no longer the same as a pointer to anobject.

Dim x As Variant

is upgraded to:

Dim x As Object


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In VB.BET the option is turned on bydefault for all new projects.

When Option Explicit Off is used (not agood programming style), you can use anyvariable without first declaring it.


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New Option in VB.NETWhen Option Strict is turned on, the

compiler/editor does not allow implicitconversions from a wider data type to a

narrower one, or between String and numericdata types CInt and CDec convert Limits erroneous numbers or run-time errors

Place the line Option Strict On before the firstline of code


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It is used to specify the type of value can beassigned for the member.

VB.NET supports two types of data types1.value type

2.Reference typeValue Type:

(a)whenever a data type is designed from structurethen it is to be Value type data type.

b)Variable information and the value will bemaintained at the stack memory.

for ex: public i as integer=10.c)value type datatypes are byte, integer, short, long,

double,decimal,boolean,char,enum etc


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byte 1 byte Range0 to 255

Unsignedbyte

sbyte 1 byte Range-128 to 127 Signedbyte

Short

(sho)

2 bytes Range

-32768 to 32767

Signed

short

ushort 2 bytes Range0 to 65535

Unsignedshort


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int(int)

4 bytes Range-2,147,483,647 to2,147,483,647

Signedinteger

uint 4 bytes Range0 to 4,294,967,295

Unsigned

integer

long(lng)

8 bytes Greater than900,000 trillion

Signedlong int

ulong 8 bytes Greater than 18million trillion

Unsignedlong int


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single

(sng)

4

bytes

Range

A number 6 digits past thedecimal

Float

number

double(dbl)

8bytes

RangeA number 14 digits past thedecimal

Doubleprecision

decimal 8bytes

RangeA number 28 zeros long

Fixedprecision

string (str) N/A Range N/A Unicode

char 2bytes

Range0x0000 to 0xFFFF

Unicodecharacter

Bool (bln) True or False Boolean


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Reference Data type:

a)whenever the data type is designed from a classdefinition then it is said to be reference type data type.

b)The variable information is maintain in the stackmemory and the value will be maintain in heapmemory.

for ex: public s string=vb.net

c)Reference type data type are string, object,interface, delegate & class.

The default modifier is private.

The default data type is an object.


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Initialize a variable at declarationDim intMax As Integer = 100IDim decRate As Decimal = 0.08D

Declare multiple variables at onceDim intCount, intNum As Integer

Convert all input to correct data type(Do not use Val function)decSale = CDec(txtSale.Text)

CInt (still rounds to even #)CDecCStr

** CInt and CDec parse some characters like $,commas,()


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New assignment Operators += = *= /= \= &= decTotal += decSale same as

decTotal=decTotal + decSale


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String ToUpper and ToLower methods Replace UCase and LCase functions If txtInput.Text.ToUpper = YES


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VB 6.0 - Arrays can be defined with lowerand upper bounds of any whole number. TheOption Base statement is used to determinethe default lower bound if a range is notspecified in the declaration.

VB.NET- To enable interoperability withother languages, all arrays must have a lowerbound of zero. This makes the Option Basestatement no longer necessary.

Dim a(1 To 10) As Stringis upgraded to:

Dim a(10) As String


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This is one area that was going to change,but did not

When you declare an array, it starts at zero, and

the element number you use is the Upper Boundof the array

This means that arrays will always be one largerthan the size declared

Dim x(2) As Integer has three elements


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Garbage Collection

The garbage collector periodicallychecks for unreferenced objectsand releases all memory andsystem resources used by theobjects

VBs garbage collection reclaimsobject space automatically behindthe scenes

For efficiency, VB only runs thegarbage collection feature when:

There are objects to recycle There is a need to recycle them


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VB 6.0 - While statements are ended with a

WEND statement.

VB.NET - WEND statements are changed to

End While. This improves language

consistency and readability.

While

End While


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Arrays in VB.NET are classes supportingproperties and methods, making themquite flexible. .Sort

.Reverse

You can sort an array in one line of code!


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VB 6.0 - Parameters that do not specifyeither ByVal or ByRef default to ByRef

VB.NET - Parameters that do not specify

either ByVal or ByRef default to ByVal.Defaulting to ByVal rather than ByRefeliminates the problem of having aprocedure mistakenly modify a variable

passed in by the caller.


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VB 6.0 - The GoSub line ... Returnstatement branches to and returns from asubroutine within a procedure.

VB.NET - GoSub...Return is anonstructured programming construct. Itsuse makes programs harder to read andunderstand. Creating separate proceduresthat you can call may provide a morestructured alternative or use casestatements.


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User Defined Types (UDTs) have beenreplaced with Structures

Structures are far more powerful than

UDTs They support the equivalent of properties and

methods

They are not as powerful as classes


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VB .NET supports such built-in functionsas FileOpen and Write These functions are found in the

Microsoft.VisualBasic namespaceVB6 code that is upgraded to VB .NET will

use these functionsThe Framework includes a rich namespace

called System.IO


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System.IO contains a large number ofclasses for handling all types of I/O

There are a variety of major categories of

objects in System.IO These include objects to manage files and

directories, read and write text files, and read andwrite binary streams


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FileInfo and DirectoryInfo classes

are for such operations as creating,moving, and deleting files and directories

If you use the Open method ofFileInfoto open a file, the returned object is aFileStream


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The StreamReader and StreamWriter

classes are common ways to perform fileI/O This can read binary and text data

The StringReader and StringWriter aredesigned to read text data


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VB .NET now supports StructuredException Handling (SEH)On Error Goto is still supported

SEH uses the TryCatchFinallysyntax

Should help reduce spaghetti code


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Overloading is the ability to have the samemethod, but with different arguments You could fake this in VB6 using ParamArrays

For example, a FindCustomer methodcould accept a customer ID, a customername, or a contact name


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Finalize will run when the object is cleanedup by the GC

You might want to release resources

explicitly, since you cannot determinewhen Finalize will be called

Use the Dispose design pattern to explicitly

free resources


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VB .NET allows you to create trulymultithreaded (or free threaded)applications

The Framework includes aSystem.Threading namespace to makeworking with threads easier

You will learn more in Chapter 11,

Multithreaded Applications


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E.g.Module Module

Enum DaysSunday=1Monday=2Tuesday=3

Wednesday=4End Enum

Sub Main()System.Console.WriteLine(Monday is day & Days.Monday)

End SubEnd Module


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It is used to initialize the members of the class.VB.net supports two types of constructors

1)Instance constructor2)shared constructor

1)Instance constructor:It is used to initialize the instance and shared

members of the class.Syntax:[modifier]Sub new([arginfo])statement(s)....End sub


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Constructors are blocks of code that runwhen a class is instantiated

Destructors are blocks of code that run

when a class drops out of memoryConstructors can be overloaded to make

them more powerfulDue to garbage collection, you cannot be

assured of when destructors will execute


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2)Shared members:

It is used to initialize the shared members ofthe class.

syntax:shared sub new()

statements

.

.

end sub

shared constructor will be invoked only once when

the class is definition is loaded


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Data abstraction or Datahiding:It is used to provide or hide the relavent

information from the user(modifiers are used).

Data encapsulation or Data binding:

it is used to identify the relavent informationand group the together(class or structure should beused)

Polymorphism(many forms):

whenever an entity can change its definitionbased on the arguments values supplied for that entitythen it is said to be supporting.


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Inheritance:

It is used to reuse or to redefine the exiting classdefinition.

Properties:

It is used to set or get the values from the privateor protected members of the class.

In order to define Readonlyproperty then get

block should be used with Readonly keyword. In oreder to define Writeonlyproperty then setblock should be used with writeonly keyword.


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Public Class Customer

Private m_CustName As String

Public Property CustomerName() As String

Get

CustomerName = m_CustName

End Get

Setm_CustName = Value

End Set

End Property

End Class

Public Class CustCompany

Inherits Customer

Private m_CustCompany As String

Public Property CustomerCompany() As String

Get

CustomerCompany = m_CustCompany

End Get

Set

m_CustCompany = Value

End Set

End Property

End Class


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It is used to modularize the flow of theapplication.

Advantage:

Easy DebuggingReusabilityPerformance

VB .NET supports two types of methods:1)Procedures or Sub routines2)Functions


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Event:These are the actions that are allowed on a control

or an object.

Event Handlers:These are the methods which provide thefunctionality or the task to be executed when ever anevent has been raised on a control.

VB supports two types of Event Handlers:Static event handlers

Dynamic event handlers


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Static Event Handlers:

whenever an event handler is defined for theobject of controls created at the design time then it is

said to be static event handler.

Dynamic Event Handlers:

whenever an event handler is defined for the

controls that are created at the runtime then it is saidto be Dynamic event handler.


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Text box:It is used to accept the singleline, multiline or

password characters as the input.

Properties:

Multiline

Scrollbars

Passwordchar

Button control

Trackbar control

Save file dialog control

Open file dialog control


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It is used to provide the browsing capabilities to thewindows form.

1)GroupBox control:

It is used to logically group the controls together.

2)Timer control:It is used to set of instructions repeatedly for every

specific interval of time.

3)ImageList control:

It is used to maintain a collection of images which canbe used by any control that has a capability to project theimage.

4)Picturebox control:

It is used to project an image

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