Android实现下拉放大图片松手自动反弹效果

import android.animation.ValueAnimator; 
import android.content.Context; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ScrollView; 
/** 
* Created by BAIPEI on 2017/11/21. 
*/ 
public class HeadZoomScrollView extends ScrollView { 
private View mZoomView; 
private int mZoomViewWidth; 
private int mZoomViewHeight; 
private float firstPosition;//记录第一次按下的位置 
private boolean isScrolling;//是否正在缩放 
private float mScrollRate = 0.3f;//缩放系数，缩放系数越大，变化的越大 
private float mReplyRate = 0.5f;//回调系数，越大，回调越慢 
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); 
} 
public void setmZoomView(View mZoomView) { 
this.mZoomView = mZoomView; 
} 
public void setmScrollRate(float mScrollRate) { 
this.mScrollRate = mScrollRate; 
} 
public void setmReplyRate(float mReplyRate) { 
this.mReplyRate = mReplyRate; 
} 
@Override 
protected void onFinishInflate() { 
super.onFinishInflate(); 
init(); 
} 
private void init() { 
setOverScrollMode(OVER_SCROLL_NEVER); 
if (getChildAt(0) != null) { 
ViewGroup vg = (ViewGroup) getChildAt(0); 
if (vg.getChildAt(0) != null) { 
mZoomView = vg.getChildAt(0); 
} 
} 
} 
@Override 
public boolean onTouchEvent(MotionEvent ev) { 
if (mZoomViewWidth <= 0 || mZoomViewHeight <= 0) { 
mZoomViewWidth = mZoomView.getMeasuredWidth(); 
mZoomViewHeight = mZoomView.getMeasuredHeight(); 
} 
switch (ev.getAction()) { 
case MotionEvent.ACTION_UP: 
//手指离开后恢复图片 
isScrolling = false; 
replyImage(); 
break; 
case MotionEvent.ACTION_MOVE: 
if (!isScrolling) { 
if (getScrollY() == 0) { 
firstPosition = ev.getY();// 滚动到顶部时记录位置，否则正常返回 
} else { 
break; 
} 
} 
int distance = (int) ((ev.getY() - firstPosition) * mScrollRate); // 滚动距离乘以一个系数 
if (distance < 0) { // 当前位置比记录位置要小，正常返回 
break; 
} 
// 处理放大 
isScrolling = true; 
setZoom(distance); 
return true; // 返回true表示已经完成触摸事件，不再处理 
} 
return true; 
} 
//回弹动画 
private void replyImage() { 
float distance = mZoomView.getMeasuredWidth() - mZoomViewWidth; 
ValueAnimator valueAnimator = ValueAnimator.ofFloat(distance, 0f).setDuration((long) (distance * mReplyRate)); 
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { 
@Override 
public void onAnimationUpdate(ValueAnimator animation) { 
setZoom((Float) animation.getAnimatedValue()); 
} 
}); 
valueAnimator.start(); 
} 
public void setZoom(float zoom) { 
if (mZoomViewWidth <= 0 || mZoomViewHeight <= 0) { 
return; 
} 
ViewGroup.LayoutParams lp = mZoomView.getLayoutParams(); 
lp.width = (int) (mZoomViewWidth + zoom); 
lp.height = (int) (mZoomViewHeight * ((mZoomViewWidth + zoom) / mZoomViewWidth)); 
((MarginLayoutParams) lp).setMargins(-(lp.width - mZoomViewWidth) / 2, 0, 0, 0); 
mZoomView.setLayoutParams(lp); 
} 
} 

<bwie.com.pulllistview.HeadZoomScrollView 
xmlns:android="http://schemas.android.com/apk/res/android" 
android:id="@+id/scrollView" 
android:layout_width="match_parent" 
android:layout_height="match_parent"  
<LinearLayout 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:orientation="vertical"  
<ImageView 
android:id="@+id/iv_show" 
android:layout_width="match_parent" 
android:layout_height="200dp" 
android:layout_weight="1" 
android:src="@drawable/a1"/  
<TextView 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:text="数据1"/  
<TextView 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:text="数据2"/  
<TextView 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:text="数据3"/  
<TextView 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:text="数据4"/  
</LinearLayout  
</bwie.com.pulllistview.HeadZoomScrollView