#1,077 – Checking for Single Modifer vs. Multiple Modifier Keys

In keypress events, you can check to see if the user is also holding down one of the modifier keys (Ctrl, Alt, Shift, or Windows key).  You do this by checking the KeyEventArgs.KeyboardDevice.Modifiers property.

You sometimes want to check to see if one and only one modifier key is being held down (e.g. Ctrl key without Alt, Shift, or Windows).  You do this by checking to see if the Modifiers property is equal to one of the ModifierKeys enumerated values.

            if ((e.Key == Key.G) &&
                (e.KeyboardDevice.Modifiers == ModifierKeys.Control))
                MessageBox.Show("Ctrl+G detected, NO Alt/Shift/Windows");

You may also want to check to see if the control key is being pressed, either alone or in conjunction with one of the other modifier keys.  You do this by using a mask.

            if ((e.Key == Key.G) &&
                ((e.KeyboardDevice.Modifiers & ModifierKeys.Control) == ModifierKeys.Control))
                MessageBox.Show("Ctrl+G or Ctrl+Alt+G, Ctrl+Alt+Windows+G, etc.");

#1,076 – Two Ways to Check for Use of Modifier Keys in Keypress Handlers

You can check for the presence of modifier keys (e.g. Alt, Ctrl, Shift, or Windows key) in keypress handlers using the KeyboardDevice.Modifier property.  For example:

        private void Window_KeyDown(object sender, KeyEventArgs e)
            if ((e.Key == Key.G) &&
                (e.KeyboardDevice.Modifiers == ModifierKeys.Control))
                MessageBox.Show("Ctrl+G detected");

Note that this method doesn’t distinguish between whether you pressed the left vs. right Ctrl keys.  This is normally what you want.  If you do want to distinguish between the two, you can explicitly check for left vs. right.

        private void Window_KeyDown(object sender, KeyEventArgs e)
            if ((e.Key == Key.G) &&
                MessageBox.Show("Left Ctrl+G detected");
            else if ((e.Key == Key.G) &&
                MessageBox.Show("Right Ctrl+G detected");

#645 – Checking for the Presence of Modifier Keys

In Windows, a modifier key is a key that you press in combination with another key.  The standard modifier keys in Windows are:

  • Alt key
  • Control (Ctrl) key
  • Shift key
  • Windows key (Windows logo on face of key)

In a WPF keypress handler (PreviewKeyDown, KeyDown, PreviewKeyUp and KeyUp), you can check for the presence of one of the modifier keys using the KeyEventArgs.KeyboardDevice.Modifiers property.  This property is an enumerated type that is a bitwise combination of the possible values.  You can check for the presence of one of the modifiers by doing an AND operation against the modifier.

        private void TextBox_PreviewKeyDown(object sender, KeyEventArgs e)
            Trace.WriteLine(string.Format("----- PreviewKeyDown for key {0}", e.Key));

            // Dumping out all modifiers
            Trace.WriteLine(string.Format("  KeyboardDevice.Modifiers = {0}", e.KeyboardDevice.Modifiers);

            // Checking for specific modifiers
            if ((e.KeyboardDevice.Modifiers & ModifierKeys.Alt) == ModifierKeys.Alt)
                Trace.WriteLine(" Alt key !");

            if ((e.KeyboardDevice.Modifiers & ModifierKeys.Control) == ModifierKeys.Control)
                Trace.WriteLine(" Ctrl key !");

Pressing Ctrl+Alt+G yields: