任意组件的回弹

package com.weidingqiang.customlistview;

/**
 * Created by weidingqiang on 15/11/28.
 */
import android.annotation.SuppressLint;
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.Scroller;
public class ScrollViewLinearLayout extends LinearLayout implements OnTouchListener{

    private LinearLayout top;
    //private LinearLayout.LayoutParams top_lp ;
    private ScrollView sv;
    private boolean isfrist =true;
    private float y1,y2;
    private int hight=60;
    private Scroller mScroller;
    public ScrollViewLinearLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        setClickable(true);
        setLongClickable(true);
        mScroller = new Scroller(context);

    }
    protected void smoothScrollBy(int dx, int dy) {
//设置mScroller的滚动偏移量
        mScroller.startScroll(0, mScroller.getFinalY(), 0, dy);
        invalidate();//这里必须调用invalidate()才能保证computeScroll()会被调用，否则不一定会刷新界面，看不到滚动效果
    }

    protected void smoothScrollTo(int fx, int fy) {
        int dx = fx - mScroller.getFinalX();
        int dy = fy - mScroller.getFinalY();
        smoothScrollBy(0, dy);
    }



    @SuppressLint("NewApi")
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if(changed&&isfrist){//只需实例化一次
            sv= (ScrollView) getChildAt(0);//该自定义布局写入xml文件时，其子布局的第一个必须是ScrollView时，这里才能getChildAt(0），实例化ScrollView
            sv.setOverScrollMode(View.OVER_SCROLL_NEVER);//去掉ScrollView 滑动到底部或顶部 继续滑动时会出现渐变的蓝色颜色快
            sv.setOnTouchListener(this);
            isfrist=false;

        }

    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) { //判断mScroller滚动是否完成
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());//这里调用View的scrollTo()完成实际的滚动
            postInvalidate();
        }
        super.computeScroll();
    }
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                y1= event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                y2= event.getY();
                int scrollY=v.getScrollY();
                int height=v.getHeight();
                int scrollViewMeasuredHeight=sv.getChildAt(0).getMeasuredHeight();
                if(y2-y1>0&&v.getScrollY()<=0){//头部回弹效果
                    smoothScrollTo(0,-(int) ((y2-y1)/2));
                    System.out.println("topMargin="+((int) ((y2-y1)/2)));
                    return false;
                }

                if(y2-y1<0&&(scrollY+height)==scrollViewMeasuredHeight){//底部回弹效果
                    smoothScrollTo(0,-(int) ((y2-y1)/2));
                    return false;
                }

                break;
            case MotionEvent.ACTION_UP:
                smoothScrollTo(0, 0);//松开手指，自动回滚
                break;
            default:
                break;
        }
        return false;
    }
}