AndroidScroll实现弹性滑动_列表下拉弹性滑动的示例代码

private void smoothScrollByScroller(int dy){
 mScroller.startScroll(0,dy,0,dy*-1,1000);
 invalidate();
}
@Override
public void computeScroll() {
 if (mScroller.computeScrollOffset()) {
  scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
  postInvalidate();
 }
}

public class MainActivity extends AppCompatActivity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
 }
}
public final class PullView extends ViewGroup {
 private int mLastY;
 private Context mContext;
 private Scroller mScroller;
 //子View的个数
 private int mChildCount;
 public PullView(Context context){
  this(context,null);
 }
 public PullView(Context context, AttributeSet attributeSet){
  super(context,attributeSet);
  mContext=context;
  initView();
 }
 private void initView(){
  mScroller=new Scroller(mContext);
 }
 @Override
 public boolean onTouchEvent(MotionEvent event) {
  int y=(int)event.getY();
  switch (event.getAction()){
   //手指按下时,初始化按下位置的X,Y位置值
   case MotionEvent.ACTION_DOWN:
    mLastY=y;
    break;
   //计算滑动的偏移量,产生滑动效果
   case MotionEvent.ACTION_MOVE:
    //手指向下滑动delayY>0，向上滑动delayY<0
    int delayY=y-mLastY;
    delayY=delayY*-1;
    scrollBy(0,delayY);
    break;
   case MotionEvent.ACTION_UP:
    /**
     * scrollY是指:View的上边缘和View内容的上边缘(其实就是第一个ChildView的上边缘)的距离
     * scrollY=上边缘-View内容上边缘，scrollTo/By方法滑动的知识View的内容
     * 往下滑动scrollY是负值
     */
    int scrollY=getScrollY();
    smoothScrollByScroller(scrollY);
    break;
  }
  mLastY=y;
  return true;
 }
 /**
  * 执行滑动效果
  * 使用scroller实现
  * @param dy
  */
 private void smoothScrollByScroller(int dy){
  mScroller.startScroll(0,dy,0,dy*-1,1000);
  invalidate();
 }
 @Override
 public void computeScroll() {
  if (mScroller.computeScrollOffset()) {
   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
   postInvalidate();
  }
 }


 /**
  * 重新计算子View的高度和宽度
  * @param widthMeasureSpec
  * @param heightMeasureSpec
  */
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  int measuredWidth;
  int measureHeight;
  mChildCount = getChildCount();
  //测量子View
  measureChildren(widthMeasureSpec, heightMeasureSpec);
  int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
  int widthSpaceMode = MeasureSpec.getMode(widthMeasureSpec);
  int heightSpaceSize = MeasureSpec.getSize(heightMeasureSpec);
  int heightSpaceMode = MeasureSpec.getMode(heightMeasureSpec);
  //获取横向的padding值
  int paddingLeft=getPaddingLeft();
  int paddingRight=getPaddingRight();
  final View childView = getChildAt(0);
  /**
   * 如果子View的数量是0,就读取LayoutParams中数据
   * 否则就对子View进行测量
   * 此处主要是针对wrap_content这种模式进行处理，因为默认情况下
   * wrap_content等于match_parent
   */
  if (mChildCount == 0) {
   ViewGroup.LayoutParams layoutParams=getLayoutParams();
   if(layoutParams!=null){
    setMeasuredDimension(layoutParams.width,layoutParams.height);
   }else {
    setMeasuredDimension(0, 0);
   }
  } else if (heightSpaceMode == MeasureSpec.AT_MOST && widthSpaceMode == MeasureSpec.AT_MOST) {
   measuredWidth = childView.getMeasuredWidth() * mChildCount;
   measureHeight = getChildMaxHeight();
   //将两侧的padding值加上去
   measuredWidth=paddingLeft+measuredWidth+paddingRight;
   setMeasuredDimension(measuredWidth, measureHeight);
  } else if (heightSpaceMode == MeasureSpec.AT_MOST) {
   measureHeight = getChildMaxHeight();
   setMeasuredDimension(widthSpaceSize, measureHeight);
  } else if (widthSpaceMode == MeasureSpec.AT_MOST) {
   measuredWidth = childView.getMeasuredWidth() * mChildCount;
   measuredWidth=paddingLeft+measuredWidth+paddingRight;
   setMeasuredDimension(measuredWidth, heightSpaceSize);
  }
 }

 /**
  * 获取子View中最大高度
  * @return
  */
 private int getChildMaxHeight(){
  int maxHeight=0;
  for (int i = 0; i < mChildCount; i++) {
   View childView = getChildAt(i);
   if (childView.getVisibility() != View.GONE) {
    int height = childView.getMeasuredHeight();
    if(height>maxHeight){
     maxHeight=height;
    }
   }
  }
  return maxHeight;
 }

 /**
  * 设置子View的布局
  * @param changed
  * @param l
  * @param t
  * @param r
  * @param b
  */
 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  int childLeft = 0;
  for (int i = 0; i < mChildCount; i++) {
   View childView = getChildAt(i);
   if (childView.getVisibility() != View.GONE) {
    int childWidth = childView.getMeasuredWidth();
    childView.layout(childLeft, 0, childLeft + childWidth, childView.getMeasuredHeight());
    childLeft += childWidth;
   }
  }
 }
}