此篇文章使用外部攔截法解決View內(nèi)外滑動方向不一致的沖突問題

1. 問題描述

外部用HorizontalScrollViewEx模擬ViewPager相艇，內(nèi)部用ListView。上下滑動則ListView滾動，左右滑動則HorizontalScrollView滾動往果。下面這篇文章已經(jīng)實(shí)現(xiàn)了HorizontalScrollView急黎，這里只解決滑動沖突問題。
4.4 View的示例(二)

2. HorizontalScrollViewEx中攔截事件

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:
                // 這里必須返回false缩幸，因?yàn)檫@里如果父View攔截了髓堪，子View收不到后續(xù)事件，應(yīng)該讓子View拿到Down事件搞坝，父View攔截Move事件搔谴。
                intercepted = false;
                if (!mscroller.isFinished()) {
                    // 沒結(jié)束，強(qiáng)制結(jié)束
                    mscroller.abortAnimation();
                    intercepted = true;
                }
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastInterceptX;
                int deltaY = y - mLastInterceptY;

                // 這里根據(jù)條件判斷是否需要攔截
                if (Math.abs(deltaX) > Math.abs(deltaY)) {
                    intercepted = true;
                } else {
                    intercepted = false;
                }
                break;
            case MotionEvent.ACTION_UP:
                // 這里返回false桩撮，因?yàn)閡p沒什么意義了
                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()) {
                    // 沒結(jié)束敦第，強(qiáng)制結(jié)束
                    mscroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                // move的時候，調(diào)用scrollBy跟著滾動就可以
                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) {
                    // 有速度則根據(jù)速度判斷上一頁或下一頁
                    // 速度為正店量，則向右正向芜果，左一頁
                    mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
                } else {
                    // 沒有速度則根據(jù)位置判斷上一頁或下一頁
                    mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
                }
                mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
                int dx = mChildIndex * mChildWidth - scrollX;
                // 使用scroller滾動
                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();
    }
}