有时GestureDetector跳过onFling

Question

我有一个使用GestureDetector的应用程序，我正在替换一些图像onDown和onFling (又名onUp)。但是，在某些情况下，不调用onFling，结果也不太好:)

您是否遇到过这样的问题，并且找到了修复/解决方法(除了使用超时)？

下面是一个小代码：

    final GestureDetector gdt1 = new GestureDetector(getApplicationContext(), new MyGestureDetector(mGestDetector, R.id.weatherFrame1));
    FrameLayout weatherFrame1 = (FrameLayout)findViewById(R.id.weatherFrame1);
    if (weatherFrame1 != null)
    {
        weatherFrame1.setOnTouchListener(new View.OnTouchListener()
        {
            @Override
            public boolean onTouch(final View view, final MotionEvent event)
            {
                gdt1.onTouchEvent(event);
                return true;
            }
        });
    }

这里是MyGestureDetector.java的一部分

    public class MyGestureDetector implements GestureDetector.OnGestureListener{
    {
    ...
        @Override
        public boolean onDown(MotionEvent e)
        {
            int index = e.getActionIndex();
            int pointerId = e.getPointerId(index);

            if (startingPointerId == -1)
            {
                Log.i("MyGestureDetector", "Pointer is " + pointerId);

                if (pointerId == 0)
                {
                    startingPosX = e.getX(pointerId);
                    startingPosY = e.getY(pointerId);
                    startingPointerId = pointerId;
                    if (null != mGestureListener)
                    {
                        mGestureListener.onDown(mGestureOrigin);
                    }
                }
            }
            return true;
        }
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
        {
            startingPointerId = -1;
            if (null != mGestureListener)
            {
                mGestureListener.onUp(mGestureOrigin);
            }
            return true;
        }
    }

Answer 1

对于检测“向上”和“向下”事件，我推荐以下简单的方法：

@Override
public boolean onTouch(final View view, final MotionEvent event) {

   if (event.getAction() == MotionEvent.ACTION_UP) {
      // handle up event
   } else if (event.getAction() == MotionEvent.ACTION_DOWN) {
      // handle down event
   }

}

编辑：不每次调用onFling最可能的原因是，它不仅仅是一种处理事件的方法。看一下安卓的源代码，只有当速度达到最低速度时才会调用onFling。看看这个：

 case MotionEvent.ACTION_UP:
        mStillDown = false;
        MotionEvent currentUpEvent = MotionEvent.obtain(ev);
        if (mIsDoubleTapping) {
            // Finally, give the up event of the double-tap
            handled |= mDoubleTapListener.onDoubleTapEvent(ev);
        } else if (mInLongPress) {
            mHandler.removeMessages(TAP);
            mInLongPress = false;
        } else if (mAlwaysInTapRegion) {
            handled = mListener.onSingleTapUp(ev);
        } else {

            // A fling must travel the minimum tap distance
            final VelocityTracker velocityTracker = mVelocityTracker;
            velocityTracker.computeCurrentVelocity(1000, mMaximumFlingVelocity);
            final float velocityY = velocityTracker.getYVelocity();
            final float velocityX = velocityTracker.getXVelocity();

            if ((Math.abs(velocityY) > mMinimumFlingVelocity)
                    || (Math.abs(velocityX) > mMinimumFlingVelocity)){
                handled = mListener.onFling(mCurrentDownEvent, ev, velocityX, velocityY);
            }
        }

最值得注意的是：

 if ((Math.abs(velocityY) > mMinimumFlingVelocity)
          || (Math.abs(velocityX) > mMinimumFlingVelocity)){
      handled = mListener.onFling(mCurrentDownEvent, ev, velocityX, velocityY);
 }

(资料来源：r1/android/view/GestureDetector.java)