如何从Xamarin Forms自定义渲染器中的视图访问方法？

Question

I have the following code:

public partial class PhrasesFrameRendererClass : Frame
{
    .....
    void getRandomWords() {
       // more code here that involves getting random numbers 
       // and updating a grid's bindingcontext
    }
}

In my custom renderer I want to be able to call the getRandomWords on swipe left gesture like below:

public class PhraseFrameCustomRenderer : FrameRenderer
{
   UISwipeGestureRecognizer leftSwipeGestureRecognizer;
   protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
   {
       base.OnElementChanged(e);
       leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
       leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
       leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
       leftSwipeGestureRecognizer.AddTarget((obj) =>
       {
          // Call getRandomWords() here
       });
   }
}

Is this possible? Any ideas on how this could be done?

Answer 1

 base.OnElementChanged(e);
   leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
   leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
   leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
   leftSwipeGestureRecognizer.AddTarget((obj) =>
   {
      // Call getRandomWords() here
      var frame = Element as PhrasesFrameRendererClass ;
      if(frame!=null){
           frame.getRandomWords();
      }
   });

Answer 2

You can create a BindableProperty of type Command in your custom frame class, call that Command from your renderer and bind your ViewModel's getRandomWords method as a Command

//Your custom control in your PCL project
public partial class PhrasesFrameRendererClass : Frame
{
    public static readonly BindableProperty SwipeLeftCommandProperty = 
    BindableProperty.Create(nameof(SwipeLeftCommand), typeof(ICommand), typeof(PhrasesFrameRendererClass ), null);

    public ICommand SwipeLeftCommand
    {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }
}

//Your custom control renderer
public class PhraseFrameCustomRenderer : FrameRenderer
{
   UISwipeGestureRecognizer leftSwipeGestureRecognizer;
   protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
   {
       base.OnElementChanged(e);
       leftSwipeGestureRecognizer = new UISwipeGestureRecognizer();
       leftSwipeGestureRecognizer.Direction = UISwipeGestureRecognizerDirection.Left;
       leftSwipeGestureRecognizer.NumberOfTouchesRequired = 1;
       leftSwipeGestureRecognizer.AddTarget((obj) =>
       {
           var myFrame = Element as PhrasesFrameRendererClassl
           if(myFrame != null){
               if(myFrame.SwipeLeftCommand != null && myFrame.SwipeLeftCommand.CanExecute()){
                   myFrame.SwipeLeftCommand.Execute();
               }
           }
       });
   }
}

//Your ViewModel
public class PhrasesViewModel{

    public Command GetRandomWordsCommand {get;set;}

    public PhrasesViewModel(){
        GetRandomWordsCommand = new Command(ExecuteGetRandomWords);
    }

    private void ExecuteGetRandomWords(){

    //Your method goes here

    }

}

//Your XAML
<yourControls:PhrasesFrameRendererClass SwipeLeftCommand="{Binding GetRandomWordsCommand }"/>

It may seem more complicated this way, but using commands allows you to separate your application code (Such as getting random phrases) from your rendering code