我们使用SwingRightInAnimationAdapter的时候你可以看到以下代码：

   

	protected final BaseAdapter mDecoratedBaseAdapter;
	private AbsListView mListView;
	public BaseAdapterDecorator(BaseAdapter baseAdapter) {
		mDecoratedBaseAdapter = baseAdapter;
	}
	public void setAbsListView(AbsListView listView) {
		mListView = listView;
		if (mDecoratedBaseAdapter instanceof BaseAdapterDecorator) {
			((BaseAdapterDecorator) mDecoratedBaseAdapter).setAbsListView(listView);
		}
		if (mListView instanceof DynamicListView) {
			DynamicListView dynListView = (DynamicListView) mListView;
			dynListView.setIsParentHorizontalScrollContainer(mIsParentHorizontalScrollContainer);
			dynListView.setDynamicTouchChild(mResIdTouchChild);
		}
	}

 

 4.2在来看看SwingRightInAnimationAdapter的源码

 SwingRightInAnimationAdapter是抽象类SingleAnimationAdapter 的子类，它继承了getAnimator()方法

 

public class SwingRightInAnimationAdapter extends SingleAnimationAdapter {
	private final long mAnimationDelayMillis;
	private final long mAnimationDurationMillis;
	public SwingRightInAnimationAdapter(BaseAdapter baseAdapter) {
		this(baseAdapter, DEFAULTANIMATIONDELAYMILLIS, DEFAULTANIMATIONDURATIONMILLIS);
	}
	public SwingRightInAnimationAdapter(BaseAdapter baseAdapter, long animationDelayMillis) {
		this(baseAdapter, animationDelayMillis, DEFAULTANIMATIONDURATIONMILLIS);
	}
	public SwingRightInAnimationAdapter(BaseAdapter baseAdapter, long animationDelayMillis, long animationDurationMillis) {
		super(baseAdapter);
		mAnimationDelayMillis = animationDelayMillis;
		mAnimationDurationMillis = animationDurationMillis;
	}
   
	@Override
	protected long getAnimationDelayMillis() {
		return mAnimationDelayMillis;
	}
	@Override
	protected long getAnimationDurationMillis() {
		return mAnimationDurationMillis;
	}
	@Override
	protected Animator getAnimator(ViewGroup parent, View view) {
		return ObjectAnimator.ofFloat(view, "translationX", parent.getWidth(), 0);
	}
}  

      而在AnimationAdapter中我们发现它重写了AnimationAdapter的getView方法(这其实就是我们的adapter的getView方法)

@Override
	public final View getView(int position, View convertView, ViewGroup parent) {
		boolean alreadyStarted = false;
		if (!mHasParentAnimationAdapter) {
			if (getAbsListView() == null) {
				throw new IllegalStateException("Call setListView() on this AnimationAdapter before setAdapter()!");
			}
			if (convertView != null) {
				alreadyStarted = cancelExistingAnimation(position, convertView);
			}
		}
		View itemView = super.getView(position, convertView, parent);
		if (!mHasParentAnimationAdapter && !alreadyStarted) {
			animateViewIfNecessary(position, itemView, parent);
		}
		return itemView;
	}

  这段代码是实现ListView item 从右往左出现动画的核心代码,思路是：

(1) 由于getView是瞬时的，为了避免item瞬时的显示出来，先要调用hideView()方法隐藏item

 

private void hideView(View view) {
		ObjectAnimator animator = ObjectAnimator.ofFloat(view, "alpha", 0);
		AnimatorSet set = new AnimatorSet();
		set.play(animator);
		set.setDuration(0);
		set.start();
	}

 

(2) 拿到item从往左显示的动画，这个动画是实质上就是SwingRightInAnimationAdapter中的getAnimator()方法

	@Override
	protected Animator getAnimator(ViewGroup parent, View view) {
		return ObjectAnimator.ofFloat(view, "translationX", parent.getWidth(), 0);
	}

 

(3) 设置item动画延迟时间  

 我们看看calculateAnimationDelay方法是怎么写的

@SuppressLint("NewApi")
	private long calculateAnimationDelay(boolean isHeader) {
		long delay;
		int numberOfItems = getAbsListView().getLastVisiblePosition() - getAbsListView().getFirstVisiblePosition();
		if (numberOfItems + 1 < mLastAnimatedPosition) {
			delay = getAnimationDelayMillis();
			if (getAbsListView() instanceof GridView && Build.VERSION.SDK_INT >= 11) {
				delay += getAnimationDelayMillis() * ((mLastAnimatedPosition + 1) % ((GridView) getAbsListView()).getNumColumns());
			}
		} else {
			long delaySinceStart = (mLastAnimatedPosition - mFirstAnimatedPosition + 1) * getAnimationDelayMillis();
			delay = mAnimationStartMillis + getInitialDelayMillis() + delaySinceStart - System.currentTimeMillis();
			delay -= isHeader && mLastAnimatedPosition > 0 ? getAnimationDelayMillis() : 0;
		}
		// System.out.println(isHeader + ": " + delay);
		return Math.max(0, delay);
	}

 

(4)开始动画集合

 

Animator[] animators = getAnimators(parent, view);
		Animator alphaAnimator = ObjectAnimator.ofFloat(view, "alpha", 0, 1);
		AnimatorSet set = new AnimatorSet();
		set.playTogether(concatAnimators(childAnimators, animators, alphaAnimator));
		set.setStartDelay(calculateAnimationDelay(isHeader));
		set.setDuration(getAnimationDurationMillis());
		set.start();

 源码就这么简单，原理就是当adapter再调用getView的时候，给每个item一个动画效果。