NestedScrollView吸顶和回弹demo

核心代码如下：

private NestedScrollView scrollView;

private int scrollDy = 0;

private int scrollOldDy = 0;

private void scrollAnimate() {
        scrollView.setOnScrollChangeListener(new View.OnScrollChangeListener() {
            @Override
            public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
                scrollDy = scrollY;
                scrollOldDy= oldScrollY;
            }
        });
        scrollView.setOnTouchListener(new View.OnTouchListener() {
            boolean result = false;
            long startTime = 0;
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        startTime = System.currentTimeMillis();
                        break;
                    case MotionEvent.ACTION_MOVE:
                        result = false;
                        break;
                    case MotionEvent.ACTION_UP:
                        long time = System.currentTimeMillis() - startTime;
                        Log.i(TAG, "onTouch: 时间：" + time);
                        if (time == 0) {
                            // 极快1毫秒
                            time = 1;
                        }
                        // 滑动的距离，正数-向上；负数-向下
                        int distant = scrollDy - scrollOldDy;
                        float speed = distant * 1f / time;
                        if (scrollDy < 150) {
                            if (speed > 0.5) {
                                // 速度大于0.5，当做快速滑动，滑动顶部
                                scrollView.smoothScrollTo(0, 300, 200);
                            } else {
                                scrollView.smoothScrollTo(0, 0, 200);
                            }
                        } else if (scrollDy < 300) {
                            if (speed < 0 && Math.abs(speed) > 0.5) {
                                scrollView.smoothScrollTo(0, 0, 200);
                            } else {
                                scrollView.smoothScrollTo(0, 300, 200);
                            }
                        }
                        Log.i(TAG, "onTouch: 起始：" + scrollOldDy);
                        Log.i(TAG, "onTouch: 结束：" + scrollDy);
                        Log.i(TAG, "onTouch: 距离：" + distant);
                        Log.i(TAG, "onTouch: 速度：" + speed);
                        result = true;
                        break;
                }
                return result;
            }
        });
    }