Android使用Scroller实现弹性滑动效果

public class SmoothScrollView extends LinearLayout{ 
 
  Scroller mScroller ; 
  int startX; 
  int startY; 
public SmoothScrollView(Context context, AttributeSet attrs) { 
  super(context, attrs); 
  //创建Scroller实例 
  mScroller = new Scroller(context); 
  } 
 
 
public void smoothScroll(int dx,int dy,int duration){ 
  //获取滑动起点坐标 
  startX = getScrollX(); 
  startY = getScrollY(); 
  //设置滑动参数 
  mScroller.startScroll(startX,startY,dx,dy,duration); 
  //重新绘制View 
  invalidate(); 
  } 
 
@Override 
public void computeScroll() { 
  // TODO Auto-generated method stub 
  super.computeScroll(); 
  boolean flag = mScroller.computeScrollOffset(); 
  //递归终止条件:滑动结束 
  if(flag == false){ 
    return; 
  }else{ 
  //mScroller.getCurrX(),mScroller.getCurrY()记录的是此刻要滑动达到的目标坐标 
  scrollTo(mScroller.getCurrX(),mScroller.getCurrY()); 
  } 
  //递归调用 
  invalidate();//或者postInvalidate() 
  } 
} 

public void startScroll(int startX, int startY, int dx, int dy, int duration) { 
    mMode = SCROLL_MODE; 
    mFinished = false; 
    mDuration = duration; 
  //记录开始滑动的时间 
    mStartTime = AnimationUtils.currentAnimationTimeMillis(); 
  //滑动起始横坐标 
    mStartX = startX; 
  //滑动起始纵坐标 
    mStartY = startY; 
  //滑动结束横坐标 
    mFinalX = startX + dx; 
  //滑动结束纵坐标 
    mFinalY = startY + dy; 
  //横向滑动偏移量 
    mDeltaX = dx; 
  //纵向滑动偏移量 
    mDeltaY = dy; 
  //mDuration表示的是整个滑动持续的时间 
    mDurationReciprocal = 1.0f / (float) mDuration; 
  } 

public boolean computeScrollOffset() { 
    if (mFinished) { 
      return false; 
    } 
 
    int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime); 
   //判断此刻是否在有效滚动周期内 
    if (timePassed < mDuration) { 
      switch (mMode) { 
      case SCROLL_MODE: 
  //当前时刻滑动偏移量所占份额 
        float x = (float)timePassed * mDurationReciprocal; 
   
        if (mInterpolator == null) 
          x = viscousFluid(x);  
        else 
          x = mInterpolator.getInterpolation(x); 
        //获取当前时刻要滚动到的位置 
        mCurrX = mStartX + Math.round(x * mDeltaX); 
        mCurrY = mStartY + Math.round(x * mDeltaY); 
        break; 
      case FLING_MODE: 
        float timePassedSeconds = timePassed / 1000.0f; 
        float distance = (mVelocity * timePassedSeconds) 
            - (mDeceleration * timePassedSeconds * timePassedSeconds / 2.0f); 
         
        mCurrX = mStartX + Math.round(distance * mCoeffX); 
        // Pin to mMinX <= mCurrX <= mMaxX 
        mCurrX = Math.min(mCurrX, mMaxX); 
        mCurrX = Math.max(mCurrX, mMinX); 
         
        mCurrY = mStartY + Math.round(distance * mCoeffY); 
        // Pin to mMinY <= mCurrY <= mMaxY 
        mCurrY = Math.min(mCurrY, mMaxY); 
        mCurrY = Math.max(mCurrY, mMinY); 
 
        if (mCurrX == mFinalX && mCurrY == mFinalY) { 
          mFinished = true; 
        } 
 
        break; 
      } 
    } 
    else { 
      mCurrX = mFinalX; 
      mCurrY = mFinalY; 
      mFinished = true; 
    } 
    return true; 
  }