How do I create compound keyboard shortcuts in a Windows Forms application?

Question

I want to create a component that allows us to have compound keyboard shortcuts associated with an arbitrary command, like the Visual Studio IDE and Microsoft Office do.

That is, keyboard shortcuts consisting of a sequence of multiple keystrokes, such as Ctrl + W + C. In Visual Studio this opens the class-view. When the first set of the keys is pressed (Ctrl + W) the message "(Ctrl + W) was pressed. Waiting for the second key of the chord..." appears in the status bar.

Answer 1

In answer to the question of keyboard chords specifically, I do not believe there is a ready-made option available to you at this point.

However, it should be simple enough to model. I would create a single class, perhaps KeyboardChordProvider. It will need to know about keyboard events at the form level. As stated elsewhere, the Form.KeyPreview property must be true. It may be enough for this provider to subscribe to the Form.KeyPress event. You could do all of this in the provider's constructor if you passed in the form.

You would need to register the potential keystrokes with the provider.

Internally this instance will track the current state. Whenever a keystroke is observed that represents the first key of the chord, you would update the provider's state and raise an event so that a subscriber could set text: (CTRL+W) was pressed. Waiting for second key of chord...

If the next keystroke matches a potential secondary option, then you have a match and could raise a ChordPressed event containing the details of the strokes entered. Alternatively, you might just call a particular callback that was given to the provider at the time the chord was registered (to avoid having a switch statement or some other dispatch in the ChordPressed event handler).

If, at any time, a keystroke does not match a potential next option, then you would reset the state of the provider.

Internal to the provider you might model the possible keystrokes using a tree structure. The current state of the provider is just a particular tree node. At the beginning, the root node would be active. If a child matches a keystroke then it becomes the current node in anticipation of the next stroke. If the child was a leaf node, then an entire chord has matched and you would raise ChordPressed event (passing the chain of strokes that got you to that point) or invoke the callback stored in the leaf. Whenever no keystroke matches a child, reset back to making the root node active.

I think this design would achieve what you want.

Answer 2

Menu controls have property named ShortCut where you can assign a value. When you press that shortcut key, that menu item will be invoked. Use that property for the commands that has a corresponding menu.

If you need shortcuts that won't be available on the menus, then you'll have to handle that your self via the KeyUp or KeyDown events, either on the form or the control. A KeyEventArgs object will be passed to your handler, and you can check which key is pressed, and whether the Ctrl, Alt or Shift keys were also pressed.

Sample code from MSDN:

// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
    // Initialize the flag to false.
    nonNumberEntered = false;

    // Determine whether the keystroke is a number from the top of the keyboard.
    if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
    {
        // Determine whether the keystroke is a number from the keypad.
        if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
        {
            // Determine whether the keystroke is a backspace.
            if(e.KeyCode != Keys.Back)
            {
                // A non-numerical keystroke was pressed.
                // Set the flag to true and evaluate in KeyPress event.
                nonNumberEntered = true;
            }
        }
    }
    //If shift key was pressed, it's not a number.
    if (Control.ModifierKeys == Keys.Shift) {
        nonNumberEntered = true;
    }
}