Question

I want that the form will not close by doing Alt + F4 but if Application.Exit() or this.Close is called from the same Form, it should be closed.

I tried CloseReason.UserClosing but still no help.

Answer 1

If you need to filter out Alt + F4 event only (leaving clicking of close box, this.Close() and Application.Exit() to behave as usual) then I can suggest the following:

1. Set form’s KeyPreview
   property to true;

2. Wire up form’s FormClosing and KeyDown events:

   private void Form1_FormClosing(object sender, FormClosingEventArgs e)
   {
       if (_altF4Pressed)
       {
           if (e.CloseReason == CloseReason.UserClosing)
               e.Cancel = true;
           _altF4Pressed = false;
       }
   }
   
   private bool _altF4Pressed;
   private void Form1_KeyDown(object sender, KeyEventArgs e)
   {
       if (e.Alt && e.KeyCode == Keys.F4)
           _altF4Pressed = true;
   }