Android ListView动画特效实现原理及源代码

Android 动画分三种，当中属性动画为我们最经常使用动画，且能满足项目中开发差点儿所有需求，google官方包支持3.0+。我们能够引用三方包nineoldandroids来失陪到低版本号。本样例中就是用属性动画实现效果。

对普通的View做动画，我们仅仅要定义好要的动画ObjectAnimator或AnimatorSet。然后设置属性启动及可。

可是。对ListView做动画应该怎样、什么时候、在什么地方、对哪个View做动画属性呢？

github上有成熟的listview动画包 https://github.com/nhaarman/ListViewAnimations.git , 基本能够满足比較炫的效果，比方google+动态list载入，各种动态list显示及删除。

问题是，假设不能满足我们的需求，怎样实现自己想要的ListView动画效果呢？研究github上项目实现原理发现并不复杂。以下我们就參考开源项目实现自己的ListView动画效果。

要想对ListView的Item做动画，首先想到的是Adapter的getView（）方法。在getView方面里能够获得每一个Item view,然后定义好动画效果，结合动画需求对contentView做动画。

如须要做一个删除item时的动画。能够在getView时把View和position传给做的动画或动画集，这个比較简单见代码：

public static AnimatorSet buildListRemoveAnimator(final View view, final List list,
final MyAnimListAdapter adapter, final int index) {
AnimatorListener al = new AnimatorListener() {

@Override
public void onAnimationStart(Animator animation) {
// TODO Auto-generated method stub

}

@Override
public void onAnimationRepeat(Animator animation) {
// TODO Auto-generated method stub

}

@Override
public void onAnimationEnd(Animator animation) {
// TODO Auto-generated method stub
list.remove(index);
ViewHolder vh = (ViewHolder) view.getTag();
vh.needInflate = true;

adapter.notifyDataSetChanged();
}

@Override
public void onAnimationCancel(Animator animation) {
// TODO Auto-generated method stub

}
};

AnimatorSet animatorSet = new AnimatorSet();
Animator anim = ObjectAnimator.ofFloat(view, "rotationX", 0, 90);
Animator animb = ObjectAnimator.ofFloat(view, "alpha", 1, 0);
ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, 1);
final int height = view.getMeasuredHeight();
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

@Override
public void onAnimationUpdate(ValueAnimator animation) {
// TODO Auto-generated method stub
if (animation.getAnimatedFraction() >= 1) {
view.setVisibility(View.GONE);
}
else {
view.getLayoutParams().height = height
- (int) (height * animation.getAnimatedFraction());
view.requestLayout();
}
}
});

anim.setDuration(ANIMATION_DURATION);
animb.setDuration(ANIMATION_DURATION);
valueAnimator.setDuration(ANIMATION_DURATION + ANIMATION_DURATION + 100);
animatorSet.playTogether(anim, animb, valueAnimator);
animatorSet.addListener(al);
return animatorSet;
}

怎样做一个listview动态现实每一个Item的显示效果。这个教删除复杂，须要计算每一个item动画的開始时间，及推断是否动画现实。还有就是显示动画要依照什么样的规则或是顺序, 计算动画现实的时间等因素。而且不好优化list的性能，及显示效果。

以下的样例仅仅是实现了基本动画效果。性能优化欠缺。

public static AnimatorSet buildShowAnimatorList(ViewGroup parent, ListView list, View view, long mAnimationStartMillis,
int mLastAnimatedPosition, int mFirstAnimatedPosition) {
if (mAnimationStartMillis == -1) {
mAnimationStartMillis = System.currentTimeMillis();
}
ViewHelper.setAlpha(view, 0);
Animator alphaAnimator = ObjectAnimator.ofFloat(view, "alpha", 0, 1);
Animator rx = ObjectAnimator.ofFloat(view, "rotationX", -90, 0);
AnimatorSet set = new AnimatorSet();
set.playTogether(alphaAnimator, rx);
set.setStartDelay(calculateAnimationDelay(list, mLastAnimatedPosition, mFirstAnimatedPosition,mAnimationStartMillis));
set.setDuration(DEFAULTANIMATIONDELAYMILLIS);
set.start();
return set;
}

private static long calculateAnimationDelay(ListView list, int last, int first,long starmill) {
long delay;

int lastVisiblePosition = list.getLastVisiblePosition();
int firstVisiblePosition = list.getFirstVisiblePosition();

int numberOfItemsOnScreen = lastVisiblePosition - firstVisiblePosition;
int numberOfAnimatedItems = last - first;

if (numberOfItemsOnScreen + 1 < numberOfAnimatedItems) {
delay = DEFAULTANIMATIONDELAYMILLIS;

} else {
long delaySinceStart = (last - first + 1)
* DEFAULTANIMATIONDELAYMILLIS;
delay = starmill + DEFAULTANIMATIONDELAYMILLIS + delaySinceStart
- System.currentTimeMillis();
}
return Math.max(0, delay);
}

參照上面的方法能够实现自己想要的ListView Item动画，而且能够去自己定义想要的效果。

本例源代码地址：
https://github.com/CankingApp/ListAnimator
多多提建议。多多交流~