Creating Events for my Classes

I see that there are BeforeDelete events in MS Office applications. If these events are set to false you can stop the program from deleting a value, page, document, or whatever event this event is fired before.

I was wondering how I couldcreate an event like this? I have a class that, of course, adds data to a collection. I want to be able to fire a BeforeAdd event that will wait for a cancel boolean. This way I will be able to validate my data in different ways and makes this class more rebust between applications.


Thanks all!

You may proceed with something like this

VB Code:

Public Class MyTestClass
 
    Public Event BeforeAdd(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)
    Public Event AfterAdd(ByVal sender As Object, ByVal e As System.EventArgs)
 
    Public Sub Add(ByVal pValueToAdd As Object)
 
        Dim MyCancelEventArg As New System.ComponentModel.CancelEventArgs(False)
 
        RaiseEvent BeforeAdd(Me, MyCancelEventArg)
 
        If MyCancelEventArg.Cancel Then
            'Do not add the value of pValueToAdd 
        Else
            'Do add the value of pValueToAdd 
            RaiseEvent AfterAdd(Me, New EventArgs)
        End If
 
    End Sub
End Class

then in form form or something

VB Code:

Public Class Form2
    Inherits System.Windows.Forms.Form
 
#Region " Windows Form Designer generated code "
 
    Private WithEvents mMyTestClass As New MyTestClass
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim MyValue As Object
        mMyTestClass.Add(MyValue)
 
    End Sub
 
 
    Private Sub mMyTestClass_AfterAdd(ByVal sender As Object, ByVal e As System.EventArgs) Handles mMyTestClass.AfterAdd
        
    End Sub
 
    Private Sub mMyTestClass_BeforeAdd(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles mMyTestClass.BeforeAdd
        'Check if i should add or not
        'Do not add
        e.Cancel = True
    End Sub
 
End Class

I have attempted this before. What happens is that the event fires but the code continues even while I am handling the event in my form.

The add method will wait for the event to finish before continuing, a bit like Calling a Function or a Sub.

Another question along the same lines, When I dim withevents myVar, I cannot use myVar in a for loop. I get this error: "Loop control variable cannot be a property or a late-bound indexed array."

What does this mean and how can I get past it and still use my variable in a loop?

I think that mean that you can't use Array in this way in the For Next Loop .. but show me some code, to be sure, of what we are talking about ;)