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>