android 出现 Error processing scroll pointer index for id

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本文分析了RecyclerView在处理滑动事件时出现的错误“Errorprocessingscroll;pointerindexforid-1notfound.DidanyMotionEventsgetskipped?”的原因及解决办法。通过对源码的深入解读，发现该错误出现在特定触控事件的处理过程中。

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1.如题出现

Error processing scroll; pointer index for id -1 not found. Did any MotionEvents get skipped?

2.原因：在recyclerView 源码的onInterceptTouchEvent的Action_move中可以发现

@Override
public boolean onInterceptTouchEvent(MotionEvent e) {
    if (mLayoutFrozen) {
        // When layout is frozen,  RV does not intercept the motion event.
        // A child view e.g. a button may still get the click.
        return false;
    }
    if (dispatchOnItemTouchIntercept(e)) {
        cancelTouch();
        return true;
    }

    if (mLayout == null) {
        return false;
    }

    final boolean canScrollHorizontally = mLayout.canScrollHorizontally();
    final boolean canScrollVertically = mLayout.canScrollVertically();

    if (mVelocityTracker == null) {
        mVelocityTracker = VelocityTracker.obtain();
    }
    mVelocityTracker.addMovement(e);

    final int action = MotionEventCompat.getActionMasked(e);
    final int actionIndex = MotionEventCompat.getActionIndex(e);

    switch (action) {
        case MotionEvent.ACTION_DOWN:
            if (mIgnoreMotionEventTillDown) {
                mIgnoreMotionEventTillDown = false;
            }
            mScrollPointerId = MotionEventCompat.getPointerId(e, 0);
            mInitialTouchX = mLastTouchX = (int) (e.getX() + 0.5f);
            mInitialTouchY = mLastTouchY = (int) (e.getY() + 0.5f);

            if (mScrollState == SCROLL_STATE_SETTLING) {
                getParent().requestDisallowInterceptTouchEvent(true);
                setScrollState(SCROLL_STATE_DRAGGING);
            }

            // Clear the nested offsets
            mNestedOffsets[0] = mNestedOffsets[1] = 0;

            int nestedScrollAxis = ViewCompat.SCROLL_AXIS_NONE;
            if (canScrollHorizontally) {
                nestedScrollAxis |= ViewCompat.SCROLL_AXIS_HORIZONTAL;
            }
            if (canScrollVertically) {
                nestedScrollAxis |= ViewCompat.SCROLL_AXIS_VERTICAL;
            }
            startNestedScroll(nestedScrollAxis);
            break;

        case MotionEventCompat.ACTION_POINTER_DOWN:
            mScrollPointerId = MotionEventCompat.getPointerId(e, actionIndex);
            mInitialTouchX = mLastTouchX = (int) (MotionEventCompat.getX(e, actionIndex) + 0.5f);
            mInitialTouchY = mLastTouchY = (int) (MotionEventCompat.getY(e, actionIndex) + 0.5f);
            break;

        case MotionEvent.ACTION_MOVE: {
            final int index = MotionEventCompat.findPointerIndex(e, mScrollPointerId); //这里必定会取出-1
            if (index < 0) {
                Log.e(TAG, "Error processing scroll; pointer index for id " +
                        mScrollPointerId + " not found. Did any MotionEvents get skipped?");
                return false;
            }

            final int x = (int) (MotionEventCompat.getX(e, index) + 0.5f);
            final int y = (int) (MotionEventCompat.getY(e, index) + 0.5f);
            if (mScrollState != SCROLL_STATE_DRAGGING) {
                final int dx = x - mInitialTouchX;
                final int dy = y - mInitialTouchY;
                boolean startScroll = false;
                if (canScrollHorizontally && Math.abs(dx) > mTouchSlop) {
                    mLastTouchX = mInitialTouchX + mTouchSlop * (dx < 0 ? -1 : 1);
                    startScroll = true;
                }
                if (canScrollVertically && Math.abs(dy) > mTouchSlop) {
                    mLastTouchY = mInitialTouchY + mTouchSlop * (dy < 0 ? -1 : 1);
                    startScroll = true;
                }
                if (startScroll) {
                    setScrollState(SCROLL_STATE_DRAGGING);
                }
            }
        } break;

        case MotionEventCompat.ACTION_POINTER_UP: {
            onPointerUp(e);
        } break;

        case MotionEvent.ACTION_UP: {
            mVelocityTracker.clear();
            stopNestedScroll();
        } break;

        case MotionEvent.ACTION_CANCEL: {
            cancelTouch();
        }
    }
    return mScrollState == SCROLL_STATE_DRAGGING;
}
4.所以在代码出返回 return super.onInterceptTouchEvent(e)