此篇文章使用外部拦截法解决View内外滑动方向不一致的冲突问题

1. 问题描述

外部用HorizontalScrollViewEx模拟ViewPager，内部用ListView。上下滑动则ListView滚动，左右滑动则HorizontalScrollView滚动。下面这篇文章已经实现了HorizontalScrollView，这里只解决滑动冲突问题。
4.4 View的示例(二)

2. HorizontalScrollViewEx中拦截事件

public class HorizontalScrollViewEx extends ViewGroup {

    private int mChildrenSize;
    private int mChildWidth;
    private int mChildIndex;

    private int mLastX;
    private int mLastY;

    private int mLastInterceptX = 0;
    private int mLastInterceptY = 0;

    private Scroller mscroller;
    private VelocityTracker mVelocityTracker;

    public HorizontalScrollViewEx(Context context, AttributeSet attrs) {
        super(context, attrs);
        mscroller = new Scroller(getContext());
        mVelocityTracker = VelocityTracker.obtain();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        boolean intercepted = false;
        int x = (int) ev.getX();
        int y = (int) ev.getY();

        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 这里必须返回false，因为这里如果父View拦截了，子View收不到后续事件，应该让子View拿到Down事件，父View拦截Move事件。
                intercepted = false;
                if (!mscroller.isFinished()) {
                    // 没结束，强制结束
                    mscroller.abortAnimation();
                    intercepted = true;
                }
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastInterceptX;
                int deltaY = y - mLastInterceptY;

                // 这里根据条件判断是否需要拦截
                if (Math.abs(deltaX) > Math.abs(deltaY)) {
                    intercepted = true;
                } else {
                    intercepted = false;
                }
                break;
            case MotionEvent.ACTION_UP:
                // 这里返回false，因为up没什么意义了
                intercepted = false;
                break;
            case MotionEvent.ACTION_CANCEL:
                break;
        }
        mLastX = x;
        mLastY = y;
        mLastInterceptX = x;
        mLastInterceptY = y;
        return intercepted;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mVelocityTracker.addMovement(event);
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (!mscroller.isFinished()) {
                    // 没结束，强制结束
                    mscroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                // move的时候，调用scrollBy跟着滚动就可以
                int deltaX = x - mLastX;
                scrollBy(-deltaX, 0);
                break;
            case MotionEvent.ACTION_UP:
                int scrollX = getScrollX();
                mVelocityTracker.computeCurrentVelocity(1000);
                float xVelocity = mVelocityTracker.getXVelocity();
                Log.e("aaa","xVelocity="+xVelocity);
                if (Math.abs(xVelocity) >= 50) {
                    // 有速度则根据速度判断上一页或下一页
                    // 速度为正，则向右正向，左一页
                    mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
                } else {
                    // 没有速度则根据位置判断上一页或下一页
                    mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
                }
                mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
                int dx = mChildIndex * mChildWidth - scrollX;
                // 使用scroller滚动
                smoothScrollBy(dx, 0);
                mVelocityTracker.clear();
                break;
            case MotionEvent.ACTION_CANCEL:
                break;
        }
        mLastX = x;
        mLastY = y;
        return super.onTouchEvent(event);
    }

    private void smoothScrollBy(int dx, int dy) {
        mscroller.startScroll(getScrollX(), 0, dx, 0, 500);
        invalidate();
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        if (mscroller.computeScrollOffset()) {
            scrollTo(mscroller.getCurrX(), mscroller.getCurrY());
            postInvalidate();
        }
    }
    @Override
    protected void onDetachedFromWindow() {
        // 做回收工作
        mVelocityTracker.recycle();
        super.onDetachedFromWindow();
    }
}