android ScrollView实现下拉放大头部图片

public class HeadZoomScrollView extends ScrollView { public HeadZoomScrollView(Context context) {  super(context); } public HeadZoomScrollView(Context context, AttributeSet attrs) {  super(context, attrs); } public HeadZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {  super(context, attrs, defStyleAttr); } // 用于记录下拉位置 private float y = 0f; // zoomView原本的宽高 private int zoomViewWidth = 0; private int zoomViewHeight = 0; // 是否正在放大 private boolean mScaling = false; // 放大的view，默认为第一个子view private View zoomView; public void setZoomView(View zoomView) {  this.zoomView = zoomView; } // 滑动放大系数，系数越大，滑动时放大程度越大 private float mScaleRatio = 0.4f; public void setmScaleRatio(float mScaleRatio) {  this.mScaleRatio = mScaleRatio; } // 最大的放大倍数 private float mScaleTimes = 2f; public void setmScaleTimes(int mScaleTimes) {  this.mScaleTimes = mScaleTimes; } // 回弹时间系数，系数越小，回弹越快 private float mReplyRatio = 0.5f; public void setmReplyRatio(float mReplyRatio) {  this.mReplyRatio = mReplyRatio; } @Override protected void onFinishInflate() {  super.onFinishInflate();//  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);//  获得默认第一个view  if (getChildAt(0) != null && getChildAt(0) instanceof ViewGroup && zoomView == null) {   ViewGroup vg = (ViewGroup) getChildAt(0);   if (vg.getChildCount() > 0) {    zoomView = vg.getChildAt(0);   }  } } @Override public boolean onTouchEvent(MotionEvent ev) {  if (zoomViewWidth <= 0 || zoomViewHeight <=0) {   zoomViewWidth = zoomView.getMeasuredWidth();   zoomViewHeight = zoomView.getMeasuredHeight();  }  if (zoomView == null || zoomViewWidth <= 0 || zoomViewHeight <= 0) {   return super.onTouchEvent(ev);  }  switch (ev.getAction()) {   case MotionEvent.ACTION_MOVE:    if (!mScaling) {     if (getScrollY() == 0) {      y = ev.getY();//滑动到顶部时，记录位置     } else {      break;     }    }    int distance = (int) ((ev.getY() - y)*mScaleRatio);    if (distance < 0) break;//若往下滑动    mScaling = true;    setZoom(distance);    return true;   case MotionEvent.ACTION_UP:    mScaling = false;    replyView();    break;  }  return super.onTouchEvent(ev); } /**放大view*/ private void setZoom(float s) {  float scaleTimes = (float) ((zoomViewWidth+s)/(zoomViewWidth*1.0));//  如超过最大放大倍数，直接返回  if (scaleTimes > mScaleTimes) return;  ViewGroup.LayoutParams layoutParams = zoomView.getLayoutParams();  layoutParams.width = (int) (zoomViewWidth + s);  layoutParams.height = (int)(zoomViewHeight*((zoomViewWidth+s)/zoomViewWidth));//  设置控件水平居中  ((MarginLayoutParams) layoutParams).setMargins(-(layoutParams.width - zoomViewWidth) / 2, 0, 0, 0);  zoomView.setLayoutParams(layoutParams); } /**回弹*/ private void replyView() {  final float distance = zoomView.getMeasuredWidth() - zoomViewWidth;  // 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 onScrollChanged(int l, int t, int oldl, int oldt) {  super.onScrollChanged(l, t, oldl, oldt);  if (onScrollListener!=null) onScrollListener.onScroll(l,t,oldl,oldt); } private OnScrollListener onScrollListener; public void setOnScrollListener(OnScrollListener onScrollListener) {  this.onScrollListener = onScrollListener; } /**滑动监听*/ public interface OnScrollListener{  void onScroll(int scrollX,int scrollY,int oldScrollX, int oldScrollY); }}