在SKCanvasView上同时使用Xamarin手势识别器与OnTouch方法的问题

你遇到的核心矛盾是：Android平台下为了让SKTouchAction.Pressed后能触发Moved事件，必须设置e.Handled = true，但这会阻断Xamarin自带GestureRecognizers的事件传递。以下是几种可行的解决方案：

方案一：Android平台自定义Renderer控制事件分发 #

针对Android平台单独处理触摸事件的传递逻辑，让SKCanvasView的OnTouch和GestureRecognizers都能处理事件：

1. 在Android项目中创建自定义Renderer：

[assembly: ExportRenderer(typeof(GestureContainer), typeof(GestureContainerRenderer))]
namespace YourAppNamespace.Droid.Renderers
{
    public class GestureContainerRenderer : SKCanvasViewRenderer
    {
        public GestureContainerRenderer(Context context) : base(context)
        {
        }

        public override bool OnTouchEvent(MotionEvent e)
        {
            // 先执行SKCanvasView的触摸处理逻辑
            base.OnTouchEvent(e);
            
            // 将事件手动传递给GestureRecognizers
            if (Element is GestureContainer gestureView)
            {
                foreach (var recognizer in gestureView.GestureRecognizers)
                {
                    if (recognizer is IGestureRecognizer androidRecognizer)
                    {
                        androidRecognizer.OnTouch(gestureView, e);
                    }
                }
            }

            return true;
        }
    }
}

2. 修改GestureContainer中的OnTouch方法，根据平台设置e.Handled：

protected override void OnTouch(SKTouchEventArgs e)
{ 
    switch (e.ActionType)
    {
         case SKTouchAction.Moved:
             // 你的移动逻辑代码
             break;
         case SKTouchAction.Pressed:
             // 你的按下逻辑代码
             break;
    }

    // Android平台设置为true保证Moved事件触发，其他平台保持false让GestureRecognizers正常工作
    e.Handled = Device.RuntimePlatform == Device.Android;
    InvalidateSurface();
}

方案二：完全基于SkiaSharp触摸事件实现手势逻辑 #

放弃Xamarin自带的GestureRecognizers，直接在OnTouch中处理双击、捏合等手势逻辑，从根源避免冲突：

public abstract class GestureContainer : SKCanvasView, IViewportable
{
    private DateTime _lastTapTime;
    private float _initialPinchDistance;
    private bool _isPinching;

    public GestureContainer()
    {
        // 无需添加Xamarin GestureRecognizers
    }

    private void TapGesture_DoubleTapped(object sender, EventArgs e)
    {
        // 双击逻辑
    }

    public void OnPinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
    {
        // 捏合逻辑
    }

    protected override void OnTouch(SKTouchEventArgs e)
    { 
        switch (e.ActionType)
        {
             case SKTouchAction.Pressed:
                 // 处理双击
                 var currentTime = DateTime.Now;
                 if ((currentTime - _lastTapTime).TotalMilliseconds < 300)
                 {
                     TapGesture_DoubleTapped(this, EventArgs.Empty);
                 }
                 _lastTapTime = currentTime;

                 // 处理捏合开始
                 if (e.InTouchPoints.Count >= 2)
                 {
                     var point1 = e.InTouchPoints[0].Location;
                     var point2 = e.InTouchPoints[1].Location;
                     _initialPinchDistance = SKPoint.Distance(point1, point2);
                     _isPinching = true;
                 }
                 break;
             case SKTouchAction.Moved:
                 // 你的移动逻辑

                 // 处理捏合更新
                 if (_isPinching && e.InTouchPoints.Count >= 2)
                 {
                     var currentDistance = SKPoint.Distance(e.InTouchPoints[0].Location, e.InTouchPoints[1].Location);
                     var scaleFactor = currentDistance / _initialPinchDistance;
                     OnPinchUpdated(this, new PinchGestureUpdatedEventArgs(GestureStatus.Running, scaleFactor, e.Location));
                     _initialPinchDistance = currentDistance;
                 }
                 break;
             case SKTouchAction.Released:
                 _isPinching = false;
                 break;
        }

        e.Handled = true; // 保证Android上Moved事件正常触发
        InvalidateSurface();
    }
}

方案三：自定义GestureRecognizer允许同时识别 #

通过自定义GestureRecognizer，允许它和SKCanvasView的触摸事件同时处理，不过这个方法在Android平台的兼容性不如前两种：

public class CustomDoubleTapGestureRecognizer : TapGestureRecognizer
{
    protected override bool ShouldRecognizeSimultaneously(IGestureRecognizer other)
    {
        return true; // 允许和其他触摸事件同时识别
    }
}

public class CustomPinchGestureRecognizer : PinchGestureRecognizer
{
    protected override bool ShouldRecognizeSimultaneously(IGestureRecognizer other)
    {
        return true;
    }
}

然后在GestureContainer的构造函数中使用这些自定义的GestureRecognizer即可。

内容的提问来源于stack exchange，提问作者Santos