Using Visual Basic .NET in Web Pages

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Using Visual Basic .NET in Web Pages

• ASP.NET

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Object-Oriented Programming (Page 1)
Open ClassVariables.aspx

• Classes and Objects
• Create objects based upon a class
• An object is a set of related code that is
  compartmentalized and built upon these classes
• Access the object across multiple Web pages
• Create an object
• The object definition, called the class
• Creating an instance of the class
• Use the class as the template ("blueprint") for
  creating the new object

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Object-Oriented Programming (Page 2)

• Multiple objects can be created (instantiated)
  from the same class definition
• Example of a class definition
• Public Class TaraStoreClass
• Private StoreName As String "Tara Store"
• End Class

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Object-Oriented Programming (Page 3)

• Restrict applications access to the class
• Publicinteract with other objects outside of the
  base class
• Privatecalled only from within the base class
• Protectedcalled from within the base class, and
  within subclasses
• Subclassa class that inherits from a base class
• Friendcalled anywhere from within the same
  application

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Object-Oriented Programming (Page 4)

• Instantiate an object based on the class
  definition
• Declare a variable
• The keyword Dim to store the object
• The keyword New to identify that this is an
  object based on a class definition
• Example
• Dim objCh5 As New TaraStoreClass()

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Object-Oriented Programming (Page 5)

• Properties
• Sets (updates) or gets (retrieves) the value of a
  variable defined within an object
• Identified by the object name, a dot (.), and the
  property name, i.e.
• objCh5.StoreName
• May be assigned a default value within the class
  definition, or the value is set as "undefined"
• All new objects inherit the same properties as
  the original object definition

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Object-Oriented Programming (Page 6)

• Inheritance
• Derives the interface and behaviors from another
  class
• The Inherits keyword allows one class to inherit
  features from another .NET class
• All objects in every VB .NET application are
  inherited from the System.Object class
• Methods from System.Object such as ToString()
  apply to most objects
• Encapsulation
• Inner workings of object are maintained within
  object

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ClassVariables.aspx
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Programmer-Defined Properties (Page 1)
Open SampleUsingVB.aspx

• Object variables store the programmer-defined
  property values
• In Visual Basic programming, they are managed
  within special Property procedures
• Used to keep object variables Private
• Property procedures are VB .NET's tools for
  providing update and retrieve capabilities
  (indirectly) for Private variables using Public
  methods
• One of the values of such methods it that they
  can provide validating techniques within the
  statements

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Programmer-Defined Properties (Page 2)

• Each of Property procedures may have two methods
• Set methods update the value of an instance
  variable
• Get methods retrieve an instance variable value
• A Property procedure that only may "set" a value
  must have the declaration WriteOnly, i.e.
• Public WriteOnly Property NewStoreEmail() As
  String
• A Property procedure that only may "get" a value
  must have the declaration ReadOnly , i.e.
• Public ReadOnly Property NewStoreName() As String

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Programmer-Defined Properties (Page 3)

• Format
• Public Property propertyName() As dataType
• Get
• statements
• End Get
• Set(ByVal varName As dataType)
• statements
• End Set
• End Property

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Programmer-Defined Properties (Page 4)

• Example
• Public Property NewStoreName() As String
• Get
• Return strStoreName
• End Get
• Set(ByVal Value As String)
• strStoreName Value
• End Set
• End Property

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The Set Method (Page 1)

• Updates the value of an instance variable
• Its always assigns either
• The Value which it gets from the variable in the
  parameter list in procedure heading
• A default value
• May only exist in a Property procedure
• Set method for a object is called when a value is
  assigned to the property of that object, i.e.
• objTS2.NewStoreName "Tara Store Chicago"

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The Set Method (Page 2)

• Format
• Set(ByVal varName As dataType)
• statements_including
• instanceVariable varName/defaultValue
• End Set
• Example
• Set(ByVal Value As String)
• strStoreName Value
• End Set

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The Get Method (Page 1)

• Retrieves the value of an instance variable
• Its always uses keyword Return along with the
  name of the instance variable (usually a single
  statement)
• Also may only exist in a Property procedure
• Get method for a object is called when the
  object's property is assigned to another
  variable, i.e.
• lblTitle.Text objTS2.NewStoreName

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The Get Method (Page 2)

• Format
• Get
• statements_including ' not likely
• Return instanceVariable
• End Get
• Example
• Get
• Return strStoreImage
• End Get

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SampleUsingVB.aspx