9.视差特效、回弹动画、overScrollBy

视差特效 
* 应用场景: 微信朋友圈, QQ空间, 微博个人展示
* 功能实现:

> 1. 之前重写onTouch, 如今重写overScrollBy

> 2. 松手之后执行动画, 类型估值器

. 

activity_main

<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

<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));
    }
	
	
	
}

MainActivity

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));
		
	}

}

来自为知笔记(Wiz)