视差特效 * 应用场景: 微信朋友圈, QQ空间, 微博个人展示，向下拉出，松开回弹 * 功能实现: > 1. 重写overScrollBy
> 2. 松手之后执行动画, 类型估值器
activity_main
代码语言：javascript复制<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
代码语言：javascript复制<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
代码语言：javascript复制 /**
* 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
代码语言：javascript复制 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
代码语言：javascript复制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));
}
}
