Android中自定义封装ScrollView类，实现上拉、下拉功能

本篇文章，自定义ScrollView，完成上拉、下拉 ,是继承的父类是ViewGroup(ScrollView)
主要代码如下：

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 isFinshAnimation = true;  //判断是否动画结束，默认是结束的

    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();  //获取坐标
        int eventY = (int) ev.getY();
        switch (ev.getAction()){
            case MotionEvent.ACTION_DOWN:
                //获取水平和垂直方向的移动距离
                lastX = downX = eventX;
                lastY = downY = eventY;
                break;
            case MotionEvent.ACTION_MOVE:
                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 || !isFinshAnimation){
            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); //延时时间

                    //设置动画监听
                    translateAnimation.setAnimationListener(new Animation.AnimationListener() {
                        @Override
                        public void onAnimationStart(Animation animation) {
                            isFinshAnimation = false;
                        }

                        @Override
                        public void onAnimationEnd(Animation animation) {
                            isFinshAnimation = true;
                            childView.clearAnimation(); //清除动画
                            //重新布局，停留在最终的位置上
                            childView.layout(normal.left,normal.top,normal.right,normal.bottom);
                            //清除normal左、上、右、下的数据
                            normal.isEmpty();
                        }

                        @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（上加"+"，下减"-"）
        if (scrollY <= 0 || scrollY >=dy){
            return true; //按照我们自定义的scrollView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;
    }
}