fling时无法左右滑动

上下滑动的RecyclerView嵌套可以左右滑动的ViewPager。
RecyclerView滑动fling时，希望能够手动左右滑动。
我们首先确定fling的触发条件：

  @Overridepublic boolean onTouchEvent(MotionEvent e) {......switch (action) {case MotionEvent.ACTION_UP: {mVelocityTracker.addMovement(vtev);eventAddedToVelocityTracker = true;mVelocityTracker.computeCurrentVelocity(1000, mMaxFlingVelocity);final float xvel = canScrollHorizontally? -mVelocityTracker.getXVelocity(mScrollPointerId) : 0;final float yvel = canScrollVertically? -mVelocityTracker.getYVelocity(mScrollPointerId) : 0;if (!((xvel != 0 || yvel != 0) && fling((int) xvel, (int) yvel))) {setScrollState(SCROLL_STATE_IDLE);}resetScroll();} break;......  }

找fling()方法，该方法又会调用mViewFlinger.fling(velocityx,velocityY)方法：

 public void fling(int velocityX, int velocityY) {setScrollState(SCROLL_STATE_SETTLING);mLastFlingX = mLastFlingY = 0;// Because you can't define a custom interpolator for flinging, we should make sure we// reset ourselves back to the teh default interpolator in case a different call// changed our interpolator.if (mInterpolator != sQuinticInterpolator) {mInterpolator = sQuinticInterpolator;mOverScroller = new OverScroller(getContext(), sQuinticInterpolator);}mOverScroller.fling(0, 0, velocityX, velocityY,Integer.MIN_VALUE, Integer.MAX_VALUE, Integer.MIN_VALUE, Integer.MAX_VALUE);postOnAnimation();}

可以看到最终mScrollState赋值为SCROLL_STATE_SETTLING。
其中mScrollState有三种状态：
1、SCROLL_STATE_IDLE = 0; 空闲状态，静止状态
2、SCROLL_STATE_IDLE = 0; 拖动状态，一般是手指滚动
3、SCROLL_STATE_IDLE = 0; 自滑动状态，一般是fling

我们手动左右滑动时继续看源码onInterceptTouchEvent：

   @Overridepublic boolean onInterceptTouchEvent(MotionEvent e) {.....switch (action) {case MotionEvent.ACTION_DOWN:......if (mScrollState == SCROLL_STATE_SETTLING) {getParent().requestDisallowInterceptTouchEvent(true);setScrollState(SCROLL_STATE_DRAGGING);stopNestedScroll(TYPE_NON_TOUCH);}......}return mScrollState == SCROLL_STATE_DRAGGING;}

在DOWN时，会赋值SCROLL_STATE_SETTLING。
返回值 mScrollState == SCROLL_STATE_DRAGGING，为true，也就是RecyclerView会在Down的时候就拦截该事件，左右滑动事件得不到响应。

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