Android自定义ScrollView实现放大回弹效果实例代码

public class ZoomInScrollView extends ScrollView {

 public ZoomInScrollView(Context context) {

    this(context, null);

  } 

  public ZoomInScrollView(Context context, AttributeSet attrs) {

    this(context, attrs, 0);

  }

  public ZoomInScrollView(Context context, AttributeSet attrs, int defStyleAttr) {

    super(context, attrs, defStyleAttr);

  }

} 

@Override

  protected void onFinishInflate() {

    super.onFinishInflate();

    //设置不可过度滚动，否则上移后下拉会出现部分空白的情况

    setOverScrollMode(OVER_SCROLL_NEVER);

    View child = getChildAt(0);

    if (child != null && child instanceof ViewGroup) {

      //获取默认第一个子View

      mHeaderView = ((ViewGroup) child).getChildAt(0);

    }

  } 

@Override

  public boolean onTouchEvent(MotionEvent ev) {

    if (mHeaderView == null)

      return super.onTouchEvent(ev);

    switch (ev.getAction()) {

      case MotionEvent.ACTION_MOVE:

        if (!mIsPulling) {

          //第一次下拉

          if (getScrollY() == 0) {

            //在顶部的时候，记录顶部位置

            mLastY = (int) ev.getY();

          } else {

            break;

          }

        }

        if (ev.getY() - mLastY < 0)

          return super.onTouchEvent(ev);

        int distance = (int) ((ev.getY() - mLastY) * mScaleRatio);

        mIsPulling = true;

        setZoom(distance);

        return true;

      case MotionEvent.ACTION_UP:

        mIsPulling = false;

        replyView();

        break;

    }

    return super.onTouchEvent(ev);

  } 

/**

 ** 放大view

 */

  private void setZoom(float s) {

    float scaleTimes = (float) ((mHeaderWidth + s) / (mHeaderWidth * 1.0));

//    如超过最大放大倍数，直接返回

    if (scaleTimes > mScaleTimes) return;

 

    ViewGroup.LayoutParams layoutParams = mHeaderView.getLayoutParams();

    layoutParams.width = (int) (mHeaderWidth + s);

    layoutParams.height = (int) (mHeaderHeight * ((mHeaderWidth + s) / mHeaderWidth));

//    设置控件水平居中

    ((MarginLayoutParams) layoutParams).setMargins(-(layoutParams.width - mHeaderWidth) / 2, 0, 0, 0);

    mHeaderView.setLayoutParams(layoutParams);

  }

 

  /**

   * 回弹

   */

  private void replyView() {

    final float distance = mHeaderView.getMeasuredWidth() - mHeaderWidth;

    // 设置动画

    ValueAnimator anim = ObjectAnimator.ofFloat(distance, 0.0F).setDuration((long) (distance * mReplyRatio));

    anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

      @Override

      public void onAnimationUpdate(ValueAnimator animation) {

        setZoom((Float) animation.getAnimatedValue());

      }

    });

    anim.start();

  }

 

@Override

  protected void onSizeChanged(int w, int h, int oldw, int oldh) {

    super.onSizeChanged(w, h, oldw, oldh);

    mHeaderWidth = mHeaderView.getMeasuredWidth();

    mHeaderHeight = mHeaderView.getMeasuredHeight();

  }