Understanding Custom Events using Visual Basic.NET 2005 (Page 1 of 5 )
This article teaches you how to declare and handle events using Visual Basic.NET 2005. It assumes the reader is familiar with object-oriented programming in Visual Basic.NET.
A
downloadable zip file is available for this article.
If you are new to OOP in Visual Basic.NET, I strongly suggest you to go through the following links:
Using Constructors with Object-Oriented Database Development
Properties and Object-Oriented Database Development
Using Methods with Object-Oriented Database Development
Inheritance with VB.NET 2005
The entire source code for this article is available in the form of a downloadable zip file. The solution was developed using Microsoft Visual Studio 2005 Professional Edition on Microsoft Windows Server 2003 Enterprise Edition. I didn't really test it in any other environment. I request that you post in the discussion area if you have any problems in execution.
A sample class without any event declarations: coding the class
Before going directly to learning about events in Visual Basic 2005, let us try to understand the following class:
Public Class Sample01
Private _x As Integer
Private _y As Integer
Public Property X() As Integer
Get
Return _x
End Get
Set(ByVal value As Integer)
_x = value
End Set
End Property
Public Property Y() As Integer
Get
Return _y
End Get
Set(ByVal value As Integer)
_y = value
End Set
End Property
Public Function GetCalculatedValue() As Double
If Me.Y <> 0 Then
Dim v As Double = Me.X / Me.Y
MessageBox.Show("Successful")
Return v
Else 'division by zero
MessageBox.Show("Division by zero is not permitted")
Return 0
End If
End Function
End Class
The above class has two private fields ("_x" and "_y") which are only accessible within the class, and not outside the class. Further, it has two public properties and a public method named "GetCalculatedValue" (public members are accessible even outside the class).
The "GetCalculatedValue" method tries to do division based on the values available in "_x" and "_y." The denominator ("_y") should never be zero during division. The "if" condition checks for the same and responds with an appropriate message.
In the next section we will try to test the above class with a Windows form.
Next: A sample class without any event declarations: testing the class >>
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