自定义ScrollView 实现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;
}
}

注意点：

1.自定义MyScrollView并获取子视图

2.重写onTouchEvent方法实现“跨界”布局--- onTouchEvent MotionEvent.ACTION_MOVE

3.使用平移动画实现MyScrollView位置还原---onTouchEvent MotionEvent.ACTION_UP