9.視差特效、回彈動畫、overScrollBy

視差特效 
* 應用場景: 微信朋友圈, QQ空間, 微博個人展示，向下拉出，松開回彈
* 功能實現:
> 1. 重寫overScrollBy

> 2. 松手之后執行動畫, 類型估值器

. 

activity_main

1. <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>

view_header

1. <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

1. /**
    * 視差特效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);
   	}
   	
   	/**
   	 * 設置ImageView圖片, 拿到引用
   	 * @param mImage
   	 */
   	public void setParallaxImage(ImageView mImage) {
   		this.mImage = mImage;
   		mOriginalHeight = mImage.getHeight(); // 160
   		drawableHeight = mImage.getDrawable().getIntrinsicHeight(); // 488,圖片的高，而不是顯示的高
   		
   		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 : 豎直方向的瞬時偏移量 / 變化量 dx   頂部到頭下拉為-, 底部到頭上拉為+
   		// scrollY : 豎直方向的偏移量 / 變化量
   		// scrollRangeY : 豎直方向滑動的范圍
   		// maxOverScrollY : 豎直方向最大滑動范圍
   		// isTouchEvent : 是否是手指觸摸滑動, true為手指, false為慣性
   		
   		Log.d(TAG, "deltaY: " +deltaY + " scrollY: " + scrollY + " scrollRangeY: " + scrollRangeY
   				+ " maxOverScrollY: " + maxOverScrollY + " isTouchEvent: " + isTouchEvent);
   		
   		// 手指拉動 並且 是下拉
   		if(isTouchEvent && deltaY < 0){
   			// 把拉動的瞬時變化量的絕對值交給Header, 就可以實現放大效果
   			if(mImage.getHeight() <= drawableHeight){
   				int newHeight = (int) (mImage.getHeight() + Math.abs(deltaY / 3.0f));
   			
   				// 高度不超出圖片最大高度時,才讓其生效
   				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:
   				// 執行回彈動畫, 方式一: 屬性動畫\值動畫
   				// 從當前高度mImage.getHeight(), 執行動畫到原始高度mOriginalHeight
   				final int startHeight = mImage.getHeight();
   				final int endHeight = mOriginalHeight;
   				
   //				valueAnimator(startHeight, endHeight);
   				// 執行回彈動畫, 方式二: 自定義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，寫幾都行
   		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;//設置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

1. 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());
   		//設置動畫執行時長
   		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;//設置imageview高
   		mImage.requestLayout();
   		
   		super.applyTransformation(interpolatedTime, t);
   	}
   	
   	
       /**
        * 類型估值器
        * @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));
       }
   	
   	
   	
   }
   

    

2. 　　MainActivity

3. 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() {
   				// 當布局填充結束之后, 此方法會被調用
   				mListView.setParallaxImage(mImage);
   				
   				mHeaderView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
   			}
   		});
   		
   		// 填充數據
   		mListView.setAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, Cheeses.NAMES));
   		
   	}
   }