Overriding a derived Event - vb.net

Question

I want to "override" an Event from a derived class - for example from a Forms-Control.
My actual state is, that the overriding (performed by the Command "Shadows") is working when I use the Handler of this Control directly.
Is the Control a member of a Collection it is only working with such Events which I have created by myself - if I try to use the overridden Event it isn't working. I suppose that the Collection uses the Event from the Base-Class.
Is that possible ?
And if "Yes" - what could I do ?
Code-Snippets from the described "Problem" :
This part collects the Event-Handler inside the Custom Control :
Private KalenderElemente As New Collection
Private Sub CreateElements()
KalenderElemente.Clear()
For i As Integer = 1 To 42
Dim myKalenderTag As New PP_Monatskalender_Tag
myKalenderTag.Name = "Tag_" + i.ToString("00")
myKalenderTag.ForeColor = my_ForeColor_Days
myKalenderTag.BackColor = my_BackColor_Days
myKalenderTag.Parent = Me
AddHandler myKalenderTag.Click, AddressOf KalenderTag_Click
AddHandler myKalenderTag.MouseMove, AddressOf KalenderTag_MouseMove
AddHandler myKalenderTag.MouseEnter, AddressOf KalenderTag_MouseEnter
AddHandler myKalenderTag.MouseLeave, AddressOf KalenderTag_MouseLeave
KalenderElemente.Add(myKalenderTag)
Next
End Sub
Private Sub Kalender_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs) Handles MyBase.MouseMove
If Not KalenderElemente.Item(0).Visible Then
KalenderElemente.Item(0).DatumsTag = 0
RaiseEvent MouseMove(KalenderElemente.Item(0), e)
Else
KalenderElemente.Item(41).DatumsTag = 0
RaiseEvent MouseMove(KalenderElemente.Item(41), e)
End If
End Sub
Private Sub KalenderTag_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs)
RaiseEvent MouseMove(sender, e)
End Sub
Shadows Event MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs)
Private Sub KalenderTag_MouseEnter(ByVal sender As Object, ByVal e As EventArgs)
RaiseEvent MouseEnter(sender, e)
End Sub
Shadows Event MouseEnter(ByVal sender As Object, ByVal e As EventArgs)
Private Sub KalenderTag_MouseLeave(ByVal sender As Object, ByVal e As EventArgs)
RaiseEvent MouseLeave(sender, e)
End Sub
Shadows Event MouseLeave(ByVal sender As Object, ByVal e As EventArgs)
Now each of the internal Controls deliver it's Mouse-Event to outside.
If I put it on a Form and write a script which takes the Event I could see that all works fine (and as expected).
In the following you see the part of the collection which should manage this Control (and others) :
Public Class MessageDefinition
Public WithEvents Control As Control
Public HeaderText As String
Public MessageText As String
Public DisplayShadow As Boolean
Public ToolTipLocation As ToolTipLocationDefintion
Public Location As Point
End Class
Public Class Message_Collection
Inherits CollectionBase
Public Shadows Sub Clear()
Dim myItem As MessageDefinition
For i As Integer = 1 To List.Count
myItem = List.Item(i - 1)
RemoveHandler myItem.Control.MouseEnter, AddressOf Item_MouseEnter
RemoveHandler myItem.Control.MouseMove, AddressOf Item_MouseMove
RemoveHandler myItem.Control.MouseLeave, AddressOf Item_MouseLeave
Next
List.Clear()
End Sub
Overrides Function ToString() As String
Return "[...]"
End Function
Public Sub Dispose()
Clear()
End Sub
' ================================
Public Sub SetMessage(item As MessageDefinition)
Dim myItem As MessageDefinition
For i As Integer = 1 To List.Count
myItem = List.Item(i - 1)
If myItem.Control.GetType Is item.Control.GetType _
AndAlso myItem.Control.Name = item.Control.Name Then
'List.Item(i - 1) = item
'RaiseEvent MouseEnter(item, System.EventArgs.Empty)
Exit Sub
End If
Next
AddHandler item.Control.MouseEnter, AddressOf Item_MouseEnter
AddHandler item.Control.MouseMove, AddressOf Item_MouseMove
AddHandler item.Control.MouseLeave, AddressOf Item_MouseLeave
List.Add(item)
RaiseEvent MouseEnter(item, System.EventArgs.Empty)
End Sub
Private Sub Item_MouseEnter(sender As Object, e As System.EventArgs)
Dim myItem As MessageDefinition
Dim mySender As Control = sender
For i As Integer = 1 To List.Count
myItem = List.Item(i - 1)
If myItem.Control Is mySender Then
RaiseEvent MouseEnter(myItem, e)
Exit Sub
End If
Next
End Sub
Private Sub Item_MouseMove(sender As Object, e As System.EventArgs)
Dim myItem As MessageDefinition
Dim mySender As Control = sender
For i As Integer = 1 To List.Count
myItem = List.Item(i - 1)
If myItem.Control Is mySender Then
RaiseEvent MouseMove(myItem, e)
Exit Sub
End If
Next
End Sub
Private Sub Item_MouseLeave(sender As Object, e As System.EventArgs)
Dim myItem As MessageDefinition
Dim mySender As Control = sender
For i As Integer = 1 To List.Count
myItem = List.Item(i - 1)
If myItem.Control Is mySender Then
RaiseEvent MouseLeave(myItem, e)
Exit Sub
End If
Next
End Sub
Public Event MouseEnter(sender As Object, e As System.EventArgs)
Public Event MouseMove(sender As Object, e As System.EventArgs)
Public Event MouseLeave(sender As Object, e As System.EventArgs)
End Class
As described (on Top) the catched Events are fired with "Standard"-Controls but not with the "Customized" Control.
If I change it and build up my own Events (with different names), which are not shadowing the Events from the derived control, it is also working as expected.

Answer 1

You don't override events in .NET - you can only override inherited event handlers, if any.
The event pattern in .NET is to create a public event in the base class and a protected virtual (VB Protected Overridable) method that raises that event and that can be overridden by a derived class. This method should be named OnEventName.
The Windows Forms controls follow this pattern, so to e.g. override when the Click event happens, you override the OnClick method:
Public Class MyTextBox
Inherits TextBox
Protected Overrides Sub OnClick(ByVal e As System.EventArgs)
If SomeCondition() Then
MyBase.OnClick(e)
Else
Return 'Do not click
End If
End Sub
End Class
Obviously you can fiddle with the e argument as well.