Android实现下拉放大图片，松手自动反弹效果

这个没啥好说的,直接看效果





下面就是代码

HeadZoomScrollView类

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);
}

}


MainActivity里面没有写代码就不粘了
下面是布局activity_main

<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>