首页3--界面上拉下拉的回弹效果

public class MyScrollView extends ScrollView {

    private View childView;

    public MyScrollView(Context context) {
        super(context);
    }

    public MyScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

//    @Override
//    protected void onLayout(boolean changed, int l, int t, int r, int b) {
//        super.onLayout(changed, l, t, r, b);
//    }

    //获取子视图
    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        if (getChildCount() > 0) {
            childView = getChildAt(0);
        }
    }

    private int lastY;//上一次y轴方向操作的坐标位置
    private Rect normal = new Rect();//用于记录临界状态的左、上、右、下
    private boolean isFinishAnimation = true;//是否动画结束

    private int lastX, downX, downY;

    //拦截:实现父视图对子视图的拦截
    //是否拦截成功，取决于方法的返回值。返回值true:拦截成功。反之，拦截失败
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        boolean isIntercept = false;
        int eventX = (int) ev.getX();
        int eventY = (int) ev.getY();
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = downX = eventX;
                lastY = downY = eventY;
                break;
            case MotionEvent.ACTION_MOVE:
                //获取水平和垂直方向的移动距离
                int absX = Math.abs(eventX - downX);
                int absY = Math.abs(eventY - downY);

                if(absY > absX && absY >= UIUtils.dp2px(10)){
                    isIntercept = true;//执行拦截
                }

                lastX = eventX;
                lastY = eventY;
                break;
        }

        return isIntercept;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (childView == null || !isFinishAnimation) {
            return super.onTouchEvent(ev);
        }

        int eventY = (int) ev.getY();//获取当前的y轴坐标
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastY = eventY;
                break;
            case MotionEvent.ACTION_MOVE:
                int dy = eventY - lastY;//微小的移动量

                if (isNeedMove()) {
                    if (normal.isEmpty()) {
                        //记录了childView的临界状态的左、上、右、下
                        normal.set(childView.getLeft(), childView.getTop(), childView.getRight(), childView.getBottom());
                    }
                    //重新布局
                    childView.layout(childView.getLeft(), childView.getTop() + dy / 2, childView.getRight(), childView.getBottom() + dy / 2);
                }

                lastY = eventY;//重新赋值
                break;
            case MotionEvent.ACTION_UP:
                if (isNeedAnimation()) {
                    //使用平移动画
                    int translateY = childView.getBottom() - normal.bottom;
                    TranslateAnimation translateAnimation = new TranslateAnimation(0, 0, 0, -translateY);
                    translateAnimation.setDuration(200);
//                translateAnimation.setFillAfter(true);//停留在最终位置上
                    translateAnimation.setAnimationListener(new Animation.AnimationListener() {
                        @Override
                        public void onAnimationStart(Animation animation) {
                            isFinishAnimation = false;
                        }

                        @Override
                        public void onAnimationEnd(Animation animation) {
                            isFinishAnimation = true;
                            childView.clearAnimation();//清除动画
                            //重新布局
                            childView.layout(normal.left, normal.top, normal.right, normal.bottom);
                            //清除normal的数据
                            normal.setEmpty();
                        }

                        @Override
                        public void onAnimationRepeat(Animation animation) {
                        }
                    });
                    //启动动画
                    childView.startAnimation(translateAnimation);
                }
                break;
        }

        return super.onTouchEvent(ev);
    }

    //判断是否需要执行平移动画
    private boolean isNeedAnimation() {
        return !normal.isEmpty();
    }

    private boolean isNeedMove() {
        int childMeasuredHeight = childView.getMeasuredHeight();//获取子视图的高度
        int scrollViewMeasuredHeight = this.getMeasuredHeight();//获取布局的高度

        Log.e("TAG", "childMeasuredHeight = " + childMeasuredHeight);
        Log.e("TAG", "scrollViewMeasuredHeight = " + scrollViewMeasuredHeight);

        int dy = childMeasuredHeight - scrollViewMeasuredHeight;//dy >= 0

        int scrollY = this.getScrollY();//获取用户在y轴方向上的偏移量 （上 + 下 -）
        if (scrollY <= 0 || scrollY >= dy) {
            return true;//按照我们自定义的MyScrollView的方式处理
        }
        //其他处在临界范围内的，返回false。即表示，仍按照ScrollView的方式处理
        return false;
    }
}