Up, Down, Left and Right arrow keys do not trigger KeyDown event

Question

I am building an application where all the key input must be handled by the windows itself.

I set tabstop to false for each control witch could grab the focus except a panel (but I don't know if it has effect).

I set KeyPreview to true and I am handling the KeyDown event on this form.

My problem is that sometimes the arrow key aren't responsive anymore:

• The keydown event is not fired when I pressed only an arrow key.

• The keydown event is fired if I press an arrow key with the control modifier.

Have you an idea why my arrow key suddenly stop firing event?

Answer 1

I was having the exact same problem. I considered the answer @Snarfblam provided; however, if you read the documentation on MSDN, the ProcessCMDKey method is meant to override key events for menu items in an application.

I recently stumbled across this article from microsoft, which looks quite promising: http://msdn.microsoft.com/en-us/library/system.windows.forms.control.previewkeydown.aspx. According to microsoft, the best thing to do is set e.IsInputKey=true; in the PreviewKeyDown event after detecting the arrow keys. Doing so will fire the KeyDown event.

This worked quite well for me and was less hack-ish than overriding the ProcessCMDKey.

Answer 2

    protected override bool IsInputKey(Keys keyData)     {         switch (keyData)         {             case Keys.Right:             case Keys.Left:             case Keys.Up:             case Keys.Down:                 return true;             case Keys.Shift | Keys.Right:             case Keys.Shift | Keys.Left:             case Keys.Shift | Keys.Up:             case Keys.Shift | Keys.Down:                 return true;         }         return base.IsInputKey(keyData);     }     protected override void OnKeyDown(KeyEventArgs e)     {         base.OnKeyDown(e);         switch (e.KeyCode)         {             case Keys.Left:             case Keys.Right:             case Keys.Up:             case Keys.Down:                 if (e.Shift)                 {                  }                 else                 {                 }                 break;                         }     }