WinUI ToggleSwitch에 Command 확장

[dimohy]

신기하게도 WinUI의 ToggleSwitch 컨트롤에 Command 속성이 없습니다. Command의 장점 중 하나가 실행할 수 없는 케이스의 경우 비활성화 하는 기능인데요, 이 기능 때문이라도 Command가 필요합니다.

시행착오가 있었습니다. Command의 CanExecuteChanged 이벤트가 발생했을 때 ToggleSwitch 컨트롤의 인스턴스를 찾아야 하는데 Attached Property로는 알 수 없으므로 Behavior로 다시 구현하였습니다. 글 오른쪽 상단의 연필 모양을 통해 시행착오를 확인하세요!

Command와 CommandParameter 기능을 확장하는 Behavior를 다음처럼 사용할 수 있게 됩니다.

| XAML

<ToggleSwitch IsOn="{x:Bind SelectedAttribute.IsKey, Mode=OneWay}">
    <interactivity:Interaction.Behaviors>
        <extensions:ToggleSwitchCommandBehavior Command="{x:Bind TogglePKCommand}" />
    </interactivity:Interaction.Behaviors>
</ToggleSwitch>

| ToggleSwitchCommandBehavior.cs

public class ToggleSwitchCommandBehavior : Behavior<ToggleSwitch>
{
    public readonly static DependencyProperty CommandProperty =
        DependencyProperty.Register(nameof(Command), typeof(ICommand), typeof(ToggleSwitchCommandBehavior),
            new PropertyMetadata(null, OnIsExternalChanged));

    public readonly static DependencyProperty CommandParameterProperty =
        DependencyProperty.Register(nameof(CommandParameter), typeof(object), typeof(ToggleSwitchCommandBehavior),
            new PropertyMetadata(null));

    private bool _isAccessUserInputProperty;

    public ICommand? Command
    {
        get => (ICommand)GetValue(CommandProperty);
        set => SetValue(CommandProperty, value);
    }

    public object? CommandParameter
    {
        get => GetValue(CommandParameterProperty);
        set => SetValue(CommandParameterProperty, value);
    }


    protected override void OnAttached()
    {
        AssociatedObject.PointerReleased += ToggleSwitch_PointerReleased;
        AssociatedObject.PreviewKeyDown += ToggleSwitch_PreviewKeyDown;
        AssociatedObject.Toggled += ToggleSwitch_Toggled;

        if (Command is not null)
        {
            Command_CanExecuteChanged(this, EventArgs.Empty);
        }
    }

    protected override void OnDetaching()
    {
        AssociatedObject.PointerReleased -= ToggleSwitch_PointerReleased;
        AssociatedObject.PreviewKeyDown -= ToggleSwitch_PreviewKeyDown;
        AssociatedObject.Toggled -= ToggleSwitch_Toggled;
    }

    private static void OnIsExternalChanged(object sender, DependencyPropertyChangedEventArgs args)
    {
        if (sender is not ToggleSwitchCommandBehavior @this)
            return;

        if (args.OldValue is ICommand oldCommand)
            oldCommand.CanExecuteChanged -= @this.Command_CanExecuteChanged;

        if (args.NewValue is ICommand newCommand)
        {
            newCommand.CanExecuteChanged += @this.Command_CanExecuteChanged;
            if (@this.AssociatedObject is not null)
                @this.Command_CanExecuteChanged(@this, EventArgs.Empty);
        }
    }

    private void Command_CanExecuteChanged(object? sender, EventArgs e)
    {
        if (Command is null)
            return;

        AssociatedObject.IsEnabled = Command.CanExecute(CommandParameter);
    }

    private void ToggleSwitch_PreviewKeyDown(object sender, KeyRoutedEventArgs e)
    {
        if (e.Key is VirtualKey.Space)
        {
            _isAccessUserInputProperty = true;
        }
    }

    private void ToggleSwitch_PointerReleased(object sender, PointerRoutedEventArgs e)
    {
        _isAccessUserInputProperty = true;
    }

    private void ToggleSwitch_Toggled(object sender, RoutedEventArgs e)
    {
        var toggleSwitch = (ToggleSwitch)sender;

        // 사용자 입력일 때만 처리하도록 한다.
        if (_isAccessUserInputProperty is false)
            return;
        _isAccessUserInputProperty = false;

        if (Command is null)
            return;

        // 커멘드에 의해 값이 변하도록 IsOn 값을 원복한다.
        toggleSwitch.IsOn = !toggleSwitch.IsOn;

        if (Command.CanExecute(CommandParameter))
            Command.Execute(CommandParameter);
    }
}