如何将 EventArgs 传递给 DelegateCommand？

Question

我有一个Xamarin.Forms 项目。在 Prism 中作为 MVVM 框架。我有一个自定义控件（源自CocosSharpView，但这并不重要）。我正在使用参数在该类中引发自定义事件，但无法将此参数传输到 ViewModel。代码如下：

查看部分。我正在启动一个带有一些参数的 custom OnTouched 事件：

public class CustomCocosSharpView : CocosSharpView
{
    public event EventHandler<CustomEventArgs> OnTouched;
    public CCGameView gameView;

    // ... not important stuff ...

    private void OnViewCreated(object sender, EventArgs ea)
    {
        if (gameView == null)
        {
            gameView = sender as CCGameView;
            if (gameView != null)
            {
                _gameScene = new GameScene(gameView);
                _gameScene.OnTouched += (s, e) =>
                {
                    CustomEventArgs custom = new CustomEventArgs() { Foo = 4 };
                    OnTouched?.Invoke(s, custom);
                };
                gameView.RunWithScene(_gameScene);
            }
        }
        OnCreated?.Invoke(sender, ea);
    }
}

public class CustomEventArgs : EventArgs
{
    public int Foo { get; set; }
}

XAML部分：

  <mobile:CustomCocosSharpView>
    <behaviors:Interaction.Behaviors>
      <behaviors:BehaviorCollection>
        <behaviors:EventToCommand EventName="OnTouched"
                                  Command="{Binding OnTouchedCommand}" />        
      </behaviors:BehaviorCollection>
    </behaviors:Interaction.Behaviors>
  </mobile:CustomCocosSharpView>

最后是 ViewModel：

    private DelegateCommand<CustomEventArgs> onTouchedCommand;
    public DelegateCommand<CustomEventArgs> OnTouchedCommand
    {
        get
        {
            return onTouchedCommand ?? (onTouchedCommand = new DelegateCommand<CustomEventArgs>((arg) =>
            {
                Debug.WriteLine("OnTouchCommand " + arg?.Foo.ToString()); //arg is null. Why?
            }));
        }
    }

问题：

如何在 DelegateCommand 中获取 CustomEventArgs 参数？ 一定可以！但没有任何效果：/

感谢您的帮助！

Answer 1

如果您使用的是 Prism 6.3-pre2，您可以使用内置的 EventToCommand 并使用转换器或路径完全控制传递给 DelegateCommand 的内容。你可以在这里查看文档：http://prismlibrary.readthedocs.io/en/latest/Xamarin-Forms/6-EventToCommandBehavior/#using-the-eventtocommandbehavior