Can window keybindings assign the press and release event individually?

Question

In WPF (XAML/C#), I can bind a hotkey on the window to execute a command, like:

<Window.InputBindings>
    <KeyBinding Modifier="Control" Key="Space" Command="{Binding TogglePushToTalk}"/>
</Window.InputBindings>

This executes the ICommand called TogglePushToTalk in my ViewModel when Ctrl+Space is pressed then subsequently released.

Is there a way to bind commands or actions to the press and release events individually, in an MVVM-friendly way, without getting into code-behind? I.e., so that pressing Ctrl+Space will execute StartPushToTalk, and then releasing those keys will call StopPushToTalk.

Answer 1

Is there a way to bind commands or actions to the press and release events individually, in an MVVM-friendly way, without getting into code-behind?

Not using pure XAML but you could implement an attached behaviour. Here is an example that should at least give you the idea:

public static class KeyBehavior
{
    public static readonly DependencyProperty KeyDownCommandProperty = DependencyProperty.RegisterAttached(
        "KeyDownCommand", typeof(ICommand), typeof(KeyBehavior), new FrameworkPropertyMetadata(new PropertyChangedCallback(OnSet)));

    public static readonly DependencyProperty KeyUpCommandProperty = DependencyProperty.RegisterAttached(
        "KeyUpCommand", typeof(ICommand), typeof(KeyBehavior));

    private static void OnSet(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Window w = (Window)d;
        w.KeyDown += OnKeyDown;
    }

    private static void OnKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Space && (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl)))
        {
            Window w = (Window)sender;
            ICommand keyDownCommand = GetKeyDownCommand(w);
            if (keyDownCommand != null)
            {
                w.KeyUp += W_KeyUp;
                keyDownCommand.Execute(null);
            }
        }
    }

    private static void W_KeyUp(object sender, KeyEventArgs e)
    {
        Window w = (Window)sender;
        w.KeyUp -= W_KeyUp;

        ICommand keyUpCommand = GetKeyUpCommand(w);
        if (keyUpCommand != null)
            keyUpCommand.Execute(null);
    }

    public static void SetKeyDownCommand(Window element, ICommand value) => element.SetValue(KeyDownCommandProperty, value);
    public static ICommand GetKeyDownCommand(Window element) => (ICommand)element.GetValue(KeyDownCommandProperty);

    public static void SetKeyUpCommand(Window element, ICommand value) => element.SetValue(KeyUpCommandProperty, value);
    public static ICommand GetKeyUpCommand(Window element) => (ICommand)element.GetValue(KeyUpCommandProperty);
}

You may want to add dependency properties for the keys in order to be able to reuse the command for several different keys and key combinations.