public class ParallaxListView extends ListView {private static final String TAG = "ParallaxListView";private ImageView ParallaxHeaderImageView;//头部视视差效果的图片private int mOldHeight;//此时ImageView的高度private int mRealHeight;//图片的真正高度public ParallaxListView(Context context) {this(context,null);}public ParallaxListView(Context context, AttributeSet attrs) {super(context, attrs);}public void setHeadImageView(ImageView ivHeadImageView) {this.ParallaxHeaderImageView = ivHeadImageView;mOldHeight = ParallaxHeaderImageView.getMeasuredHeight();
//        int height = ParallaxHeaderImageView.getHeight();
//        Log.e(TAG,mOldHeight+"----"+height);//两个值一样mRealHeight = ParallaxHeaderImageView.getDrawable().getIntrinsicHeight();}@Overrideprotected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {System.out.println("deltaY: "+ deltaY + " scrollY: " + scrollY+ " scrollRangeY: " + scrollRangeY+ " maxOverScrollY: " + maxOverScrollY+ " isTouchEvent: " + isTouchEvent);// deltaY : 竖直方向的瞬时偏移量, 顶部下拉- , 底部上拉+, 速度越快绝对值越大.// scrollY : 竖直方向ListView滚动的距离, 顶部- , 底部+// scrollRangeY : 竖直方向滚动距离// maxOverScrollY : 最大的超出滚动范围// isTouchEvent : 是否是手指触摸到顶部/底部. true触摸, false惯性if(deltaY <0 && isTouchEvent){int newHeight = ParallaxHeaderImageView.getHeight() + Math.abs(deltaY)/2;//减少拖动的距离setCurrentImageViewHeight(newHeight);}return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);}private void setCurrentImageViewHeight(int newHeight) {ParallaxHeaderImageView.getLayoutParams().height = newHeight;ParallaxHeaderImageView.requestLayout();}@Overridepublic boolean onTouchEvent(MotionEvent ev) {switch (ev.getAction()) {case MotionEvent.ACTION_UP:int startHeight = ParallaxHeaderImageView.getHeight();ValueAnimator animator = ValueAnimator.ofInt(startHeight, mOldHeight);animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {// 500 毫秒内多次调用// 0.0 -> 1.0System.out.println("animation: " + animation.getAnimatedFraction());// 模拟出来的中间值Object animatedValue = animation.getAnimatedValue();System.out.println("animation: " + animatedValue);// 让新的高度生效setCurrentImageViewHeight((Integer)animatedValue);}});animator.setInterpolator(new OvershootInterpolator(4));animator.setDuration(500);animator.start();break;default:break;}return super.onTouchEvent(ev);}
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/activity_main"android:layout_width="match_parent"android:layout_height="match_parent"tools:context="com.itydl.a04.MainActivity"><com.itydl.a04.view.ParallaxListViewandroid:id="@+id/lv"android:layout_width="match_parent"android:layout_height="match_parent"/></RelativeLayout>

@Override
protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mListView = (ParallaxListView) findViewById(R.id.lv);mHeadView = View.inflate(this, R.layout.layout_head,null);mIvHead = (ImageView) mHeadView.findViewById(R.id.iv);mListView.addHeaderView(mHeadView);mIvHead.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {@Overridepublic void onGlobalLayout() {mListView.setHeadImageView(mIvHead);mIvHead.getViewTreeObserver().removeGlobalOnLayoutListener(this);}});mListView.setAdapter(new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,Strings.NAMES));
}

    if(deltaY <0 && isTouchEvent){int newHeight = ParallaxHeaderImageView.getHeight() + Math.abs(deltaY)/2;//减少拖动的距离if(newHeight <= mRealHeight){//只有在滑动的距离小于图片的真正高度的时候才去重新设置，超过了图片的高度就不去设置了。setCurrentImageViewHeight(newHeight);}}