System.ObjectDisposedException：无法访问已处置的对象-为什么发生？

Question

I got the error having the stack trace...

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)

The code producing this error is....

Friend Sub GoHome(ByVal sender As Form)
  InTransit = True
  sender.Close()
  fMain.Show()
End Sub

It doesn't give error when I just switch the order of the .show and .close method

Friend Sub GoHome(ByVal sender As Form)
  InTransit = True
  fMain.Show()
  sender.Close()
End Sub

Can you please tell me why for the first case it gives error and why in second case it doesn't??

Answer 1

Are sender and fMain the same object in this case?

If so... when you call sender.Close you're effectively calling fMain.Close , and the Close method will be disposing that object behind-the-scenes. If you subsequently call fMain.Show then you're calling it on an object that you just disposed, hence the error.

Or, alternatively...

Maybe sender is one of the child controls on fMain ?

You call sender.Close , disposing the child control. You then call fMain.Show which attempts to do something with the child controls belonging to fMain . The error occurs when it tries to do that particular something with the child control that you just disposed.