Disable Alt+F4 but allow the the form to be closed by code, CloseReason.UserClosing is not helping

问题

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.

回答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;
   }
   

回答2:

It's very easy you can do it by set SuppressKeyPress property to true on Form_Keydown EventHandler as below.

        if (e.KeyCode == Keys.F4 && e.Alt)
        {
            e.SuppressKeyPress = true;

        }

With this you can also close your active form by set SuppressKeyPress Property to false on same eventHandller or any other way.

回答3:

Capture Alt+F4 hotkey by setting Form's KeyPreview property to true and overriding OnProcessCmdKey method.

回答4:

How did you use CloseReason?

See the sample code here: http://msdn.microsoft.com/en-us/library/system.windows.forms.form.formclosing.aspx

You need to set the Cancel property of the passed FormClosingEventArgs object to stop the form closing.

来源：https://stackoverflow.com/questions/2643712/disable-altf4-but-allow-the-the-form-to-be-closed-by-code-closereason-userclos