How can I know if a .net event is already handled?

Question

I\'ve written some code to handle an event as follows:

AddHandler myObject.myEvent, AddressOf myFunction

It seemed that everything was work

Answer 1

You may use IsHandleCreated property to check your event already has an handle or not.

  If e.Control.IsHandleCreated = False Then
            AddHandler e.Control.KeyPress, AddressOf TextBox_keyPress
  End If

Answer 2

I know I am a few years late to the game but you could always scope a class variable and then set it after the fact. This is not a totally hardened way of doing things but it is better than just hoping you did not have something or re adding it every time. In my case I used this in a WinForms app were I wanted to add a handler for dragging and dropping onto a datagridview surface. I wanted to stop this functionality if part of another datagridview was not yet filled out completely that it was dependent on.

So it would be like this:

Class level

Private _handlersAdded As Boolean = False

Constructor:

Public Sub New()
  AddHandler dgv.DragEnter, AddressOf DragEnter
  _handlersAdded = True
End Sub

Method that determines issue:

Private Sub CheckRowsAreDone()
  For Each row As DataGridViewRow In dgv.Rows
    Dim num = 0

    For i = 0 To row.Cells.Count - 1
      Dim val = If(Not String.IsNullOrEmpty(row?.Cells(i)?.Value?.ToString), 1, -1)
      num += val
    Next

    If num > -(row.Cells.Count) And num < (row.Cells.Count) Then
      RemoveHandler dgv.DragEnter, AddressOf DragEnter
      _handlersAdded = False
      Exit Sub
    End If

    If Not _handlersAdded Then
      AddHandler dgv.DragEnter, AddressOf DragEnter
      _handlersAdded = True
    End If

    Next
End Sub