ObjectDisposedException from core .NET code
- by John
I'm having this issue with a live app.
(Unfortunately this is post-mortem debugging - I only have this stack trace. I've never seen this personally, nor am I able to reproduce).
I get this Exception:
message=Cannot access a disposed object.
Object name: 'Button'.
exceptionMessage=Cannot access a disposed object.
Object name: 'Button'.
exceptionDetails=System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'Button'.
at System.Windows.Forms.Control.CreateHandle()
at System.Windows.Forms.Control.get_Handle()
at System.Windows.Forms.Control.PointToScreen(Point p)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
exceptionSource=System.Windows.Forms
exceptionTargetSite=Void CreateHandle()
It looks like a mouse event is arriving at a form after the form has been disposed.
Note there is none of my code in this stack trace.
The only weird (?) thing I'm doing, is that I do tend to Dispose() Forms quite aggressively when I use them with ShowModal() (see "Aside" below).
But I only do this after ShowModal() has returned (that should be safe right)?
I think I read that events might be queued up in the event queue, but I can't believe this would be the problem. I mean surely the framework must be tolerant to old messages? I can well imagine that under stress messages might back-log and surely the window might go away at any time?
Any ideas?
If you could even suggest ways of reproducing, that might be useful.
John
Aside:
TBH I've never quite understood whether calling Dispose() after Form.ShowDialog() is strictly necessary - the MSDN docs for ShowDialog() are to my mind a bit ambiguous.
