9.视差特效、回弹动画、overScrollBy

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".MainActivity" >
 <com.itheima.parallaxdemo.ui.MyListView
 android:id="@+id/lv"
 android:layout_width="match_parent"
 android:layout_height="match_parent" />
</RelativeLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >
 <ImageView
 android:id="@+id/iv"
 android:layout_width="match_parent"
 android:layout_height="160dp"
 android:scaleType="centerCrop"
 android:src="@drawable/parallax_img" />
</LinearLayout>

MyListView
 
 /**
 * 视差特效ListView
 * overScrollBy
 * @author poplar
 *
 */
public class MyListView extends ListView {
 private static final String TAG = "TAG";
 private int mOriginalHeight;
 private int drawableHeight;
 private ImageView mImage;
 public MyListView(Context context, AttributeSet attrs, int defStyle) {
 super(context, attrs, defStyle);
 }
 public MyListView(Context context, AttributeSet attrs) {
 super(context, attrs);
 }
 public MyListView(Context context) {
 super(context);
 }
 /**
 * 设置ImageView图片, 拿到引用
 * @param mImage
 */
 public void setParallaxImage(ImageView mImage) {
 this.mImage = mImage;
 mOriginalHeight = mImage.getHeight(); // 160
 drawableHeight = mImage.getDrawable().getIntrinsicHeight(); // 488,图片的高，而不是显示的高
 Log.d(TAG, "height: " + mOriginalHeight + " drawableHeight: " + drawableHeight);
 }
 @Override
 protected boolean overScrollBy(int deltaX, int deltaY,
 int scrollX, int scrollY, int scrollRangeX, int scrollRangeY,
 int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
 // deltaY : 竖直方向的瞬时偏移量 / 变化量 dx   顶部到头下拉为-, 底部到头上拉为+
 // scrollY : 竖直方向的偏移量 / 变化量
 // scrollRangeY : 竖直方向滑动的范围
 // maxOverScrollY : 竖直方向最大滑动范围
 // isTouchEvent : 是否是手指触摸滑动, true为手指, false为惯性
 Log.d(TAG, "deltaY: " +deltaY + " scrollY: " + scrollY + " scrollRangeY: " + scrollRangeY
 + " maxOverScrollY: " + maxOverScrollY + " isTouchEvent: " + isTouchEvent);
 // 手指拉动 并且 是下拉
 if(isTouchEvent && deltaY < 0){
 // 把拉动的瞬时变化量的绝对值交给Header, 就可以实现放大效果
 if(mImage.getHeight() <= drawableHeight){
 int newHeight = (int) (mImage.getHeight() + Math.abs(deltaY / 3.0f));
 // 高度不超出图片最大高度时,才让其生效
 mImage.getLayoutParams().height = newHeight;
 mImage.requestLayout();
 }
 }
 return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX,
 scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);
 }
 @Override
 public boolean onTouchEvent(MotionEvent ev) {
 switch (ev.getAction()) {
 case MotionEvent.ACTION_UP:
 // 执行回弹动画, 方式一: 属性动画\值动画
 // 从当前高度mImage.getHeight(), 执行动画到原始高度mOriginalHeight
 final int startHeight = mImage.getHeight();
 final int endHeight = mOriginalHeight;
//              valueAnimator(startHeight, endHeight);
 // 执行回弹动画, 方式二: 自定义Animation
 ResetAnimation animation = new ResetAnimation(mImage, startHeight, endHeight);
 startAnimation(animation);
 break;
 }
 return super.onTouchEvent(ev);
 }
 private void valueAnimator(final int startHeight, final int endHeight) {
 ValueAnimator mValueAnim = ValueAnimator.ofInt(1);//不起作用，写几都行
 mValueAnim.addUpdateListener(new AnimatorUpdateListener() {
 @Override
 public void onAnimationUpdate(ValueAnimator mAnim) {
 float fraction = mAnim.getAnimatedFraction();
 // percent 0.0 -> 1.0
 Log.d(TAG, "fraction: " +fraction);
 Integer newHeight = evaluate(fraction, startHeight, endHeight);//固值器
 mImage.getLayoutParams().height = newHeight;//设置imageview高度
 mImage.requestLayout();
 }
 });
 mValueAnim.setInterpolator(new OvershootInterpolator());
 mValueAnim.setDuration(500);
 mValueAnim.start();
 }
 public Integer evaluate(float fraction, Integer startValue, Integer endValue) {
 int startInt = startValue;
 return (int)(startInt + fraction * (endValue - startInt));
 }
}

ResetAnimation
 
  public class ResetAnimation extends Animation {
 private final ImageView mImage;
 private final int startHeight;
 private final int endHeight;
 public ResetAnimation(ImageView mImage, int startHeight, int endHeight) {
 this.mImage = mImage;
 this.startHeight = startHeight;
 this.endHeight = endHeight;
 setInterpolator(new OvershootInterpolator());
 //设置动画执行时长
 setDuration(500);
 }
 @Override
 protected void applyTransformation(float interpolatedTime, Transformation t) {
 // interpolatedTime 0.0f -> 1.0f
 Integer newHeight = evaluate(interpolatedTime, startHeight, endHeight);
 mImage.getLayoutParams().height = newHeight;//设置imageview高
 mImage.requestLayout();
 super.applyTransformation(interpolatedTime, t);
 }
 /**
 * 类型估值器
 * @param fraction
 * @param startValue
 * @param endValue
 * @return
 */
 public Integer evaluate(float fraction, Integer startValue, Integer endValue) {
 int startInt = startValue;
 return (int)(startInt + fraction * (endValue - startInt));
 }
}
 

public class MainActivity extends Activity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 final MyListView mListView = (MyListView) findViewById(R.id.lv);
 mListView.setOverScrollMode(View.OVER_SCROLL_NEVER);
 // 加Header
 final View mHeaderView = View.inflate(MainActivity.this, R.layout.view_header, null);
 final ImageView mImage = (ImageView) mHeaderView.findViewById(R.id.iv);
 mListView.addHeaderView(mHeaderView);
 mHeaderView.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
 @Override
 public void onGlobalLayout() {
 // 当布局填充结束之后, 此方法会被调用
 mListView.setParallaxImage(mImage);
 mHeaderView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
 }
 });
 // 填充数据
 mListView.setAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, Cheeses.NAMES));
 }
}