Override standard close (X) button in a Windows Form

Question

How do I go about changing what happens when a user clicks the close (red X) button in a Windows Forms application (in C#)?

Answer 1

One situation where it is quite useful to be able to handle the x-button click event is when you are using a Form that is an MDI container. The reason is that the closeing and closed events are raised first with children and lastly with the parent. So in one scenario a user clicks the x-button to close the application and the MDI parent asks for a confirmation to proceed. In case he decides to not close the application but carry on whatever he is doing the children will already have processed the closing event potentially lost information/work whatever. One solution is to intercept the WM_CLOSE message from the Windows message loop in your main application form (i.e. which closed, terminates the application) like so:

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0x0010) // WM_CLOSE
        {
            // If we don't want to close this window 
            if (ShowConfirmation("Are you sure?") != DialogResult.Yes) return;
        }

        base.WndProc(ref m);
    }