MessageBox not showing from modal dialog window

Question

I am trying to show a message box when an error occurs in a modal dialog window but for some reason the message box is never shown although I know the MessageBox.Show method is being hit. The try catch block is inside of an event handler for a windows form that is being shown as a modal dialog. I know that the event is being fired and that the error is being caught but the message box never opens. I've replaced the MessageBox.Show with another form show and it works fine but I'd rather use MessageBox instead of creating my own error form. I just can't seem to make MessageBox work. Is this a limitation of MessageBox?

Here is a simplified version of what I am doing:

Private Sub OnSomeEvent(ByVal args As MyEventArgs) 
  Try
    'some processing
  Catch ex As Exception
    ShowMessage("An error has occurred")
  End Try
End Sub

Private Delegate Sub _showMessage(ByVal message As String)
Private Sub ShowMessage(ByVal message As String)
  If Me.InvokeRequired Then
    Me.Invoke(New _showMessage(AddressOf ShowMessage), message)
  Else
    MessageBox.Show(message, "ERROR")
    'also tried MessageBox.Show(Me, message) but no luck
  End If
End Sub

*side note: In this case I do not need the InvokeRequired section of ShowMessage but I left it in for completeness (in case somehow that could be causing the issue). I have it there for other cases when it is called from a background thread. In this particular instance when debugging, it goes through the Else branch.

Is it possible that the messagebox is appearing under the dialog? — Mark Ransom
Although that seems like the logical answer, I don't believe so. I've moved the dialog all over the screen and still no MessageBox in site. It doesn't show up as a window in the taskbar either. — TKTS

Ignacio Soler Garcia Ignacio Soler Garcia · Accepted Answer · 2012-01-26T12:09:22

Check if the main thread is blocked doing some other task. Then the call will be blocked on the Me.Invoke(New _showMessage(AddressOf ShowMessage), message) and you won't see the MessageBox.

What happens if you put a breakpoint at the MessageBox.Show(message, "ERROR")?

MessageBox not showing from modal dialog window

1 Answers