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>

 /**
 * 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));
    }
     
     
}

  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));
         
    }
}