@author:莫川
为RecyclerView的Item添加动画有很多中方案，比如通过设置setItemAnimator来实现或者是通过遍历RecyclerView中的子View，然后分别对子View做动画。今天介绍一种更加简单的方式：通过LayoutAnimationController的方式，对RecyclerView的Item做动画。
先看效果：首先是对LinearLayoutManager的RecyclerView。
1.使用LayoutAnimationController的8种动画的播放效果 2.使用GridLayoutAnimationController的8种动画的播放效果比如实现从依次从左侧进入的动画效果，我们首先需要实现一个Item的动画效果，然后创建一个LayoutAnimationController对象，并设置每一个item播放动画的时间延时和item的播放顺序。
以从左侧进入为例，每个单独的Item的动画如下：
1.Item动画 ... /** * 从左侧进入，并带有弹性的动画 * * @return */ public static AnimationSet getAnimationSetFromLeft() { AnimationSet animationSet = new AnimationSet(true); TranslateAnimation translateX1 = new TranslateAnimation(RELATIVE_TO_SELF, -1.0f, RELATIVE_TO_SELF, 0.1f, RELATIVE_TO_SELF, 0, RELATIVE_TO_SELF, 0); translateX1.setDuration(300); translateX1.setInterpolator(new DecelerateInterpolator()); translateX1.setStartOffset(0); TranslateAnimation translateX2 = new TranslateAnimation(RELATIVE_TO_SELF, 0.1f, RELATIVE_TO_SELF, -0.1f, RELATIVE_TO_SELF, 0, RELATIVE_TO_SELF, 0); translateX2.setStartOffset(300); translateX2.setInterpolator(new DecelerateInterpolator()); translateX2.setDuration(50); TranslateAnimation translateX3 = new TranslateAnimation(RELATIVE_TO_SELF, -0.1f, RELATIVE_TO_SELF, 0f, RELATIVE_TO_SELF, 0, RELATIVE_TO_SELF, 0); translateX3.setStartOffset(350); translateX3.setInterpolator(new DecelerateInterpolator()); translateX3.setDuration(50); animationSet.addAnimation(translateX1); animationSet.addAnimation(translateX2); animationSet.addAnimation(translateX3); animationSet.setDuration(400); return animationSet; } ...为了让Item看起来有‘弹性’效果，animationSet添加了三个移动动画，分别是从左侧进入(-100%)，移动到右侧的10%,然后在从右侧(10%)移动到左侧(-10%),最后再从(-10%)移动到原本的位置(0%)。这样就有了移动后的弹性效果。
2.设置LayoutAnimationController的属性2.1 设置ViewGroup的子View播放动画之间的offset。
/** * Sets the delay, as a fraction of the animation duration, by which the children's animations are offset. */ void setDelay(float delay)2.2 设置ViewGroup的子View播放动画的顺序
/** * Sets the order used to compute the delay of each child's animation. */ void setOrder(int order)setOrder可以取值为LayoutAnimationController.ORDER_NORMAL(正常顺序)，LayoutAnimationController.ORDER_RANDOM(随机顺序)以及LayoutAnimationController.ORDER_REVERSE(逆序)。这里的demo设置的是正常顺序。
3.播放动画 /** * 播放RecyclerView动画 * * @param animation * @param isReverse */ public void playLayoutAnimation(Animation animation, boolean isReverse) { LayoutAnimationController controller = new LayoutAnimationController(animation); controller.setDelay(0.1f); controller.setOrder(isReverse ? LayoutAnimationController.ORDER_REVERSE : LayoutAnimationController.ORDER_NORMAL); mRecyclerView.setLayoutAnimation(controller); mRecyclerView.getAdapter().notifyDataSetChanged(); mRecyclerView.scheduleLayoutAnimation(); }通过viewGroup.setLayoutAnimation设置layout动画。然后通知ViewGroup重新绘制，调用scheduleLayoutAnimation方法播放动画。
上述方法针对的是线性的RecyclerView，也就是说RecyclerView的LayoutManager设置的是LinearLayoutManager.
... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main_list); Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar); mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view); mRecyclerView.setLayoutManager(new LinearLayoutManager(this)); mRecyclerView.setAdapter(new DemoRecyclerViewAdapter()); } ...而对于使用GridLayoutManager和StaggeredGridLayoutManager的RecyclerView来说，我们需要使用GridLayoutAnimationController，其他步骤与LayoutAnimationController一致。
... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main_grid); Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar); mRecyclerView = (StaggeredGridRecyclerView) findViewById(R.id.recycler_view); mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)); mStaggeredGridAdapter = new StaggeredGridAdapter(); mStaggeredGridAdapter.setDataSet(mockData()); mRecyclerView.setAdapter(mStaggeredGridAdapter); } ....同样的，仍然使用之前的Animation创建GridLayoutAnimationController。
... /** * 播放动画 * * @param animation * @param isReverse */ public void playLayoutAnimation(Animation animation, boolean isReverse) { GridLayoutAnimationController controller = new GridLayoutAnimationController(animation); controller.setColumnDelay(0.2f); controller.setRowDelay(0.3f); controller.setOrder(isReverse ? LayoutAnimationController.ORDER_REVERSE : LayoutAnimationController.ORDER_NORMAL); mRecyclerView.setLayoutAnimation(controller); mRecyclerView.getAdapter().notifyDataSetChanged(); mRecyclerView.scheduleLayoutAnimation(); } ...GridLayoutAnimationController的delay方法可以分别按照Column和Row维度进行设置。
本以为到此顺利结束。运行后发现，会Crash，log为：
... E/AndroidRuntime( 7876): java.lang.ClassCastException: android.view.animation.LayoutAnimationController$AnimationParameters cannot be cast to android.view.animation.GridLayoutAnimationController$AnimationParameters E/AndroidRuntime( 7876): at android.view.animation.GridLayoutAnimationController.getDelayForView(GridLayoutAnimationController.java:299) E/AndroidRuntime( 7876): at android.view.animation.LayoutAnimationController.getAnimationForView(LayoutAnimationController.java:321) E/AndroidRuntime( 7876): at android.view.ViewGroup.bindLayoutAnimation(ViewGroup.java:4227) E/AndroidRuntime( 7876): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3272) E/AndroidRuntime( 7876): at android.view.View.draw(View.java:15618) E/AndroidRuntime( 7876): at android.support.v7.widget.RecyclerView.draw(RecyclerView.java:3869) E/AndroidRuntime( 7876): at android.view.View.updateDisplayListIfDirty(View.java:14495) E/AndroidRuntime( 7876): at android.view.View.getDisplayList(View.java:14524) E/AndroidRuntime( 7876): at android.view.View.draw(View.java:15315) E/AndroidRuntime( 7876): at android.view.ViewGroup.drawChild(ViewGroup.java:3536) E/AndroidRuntime( 7876): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3329) E/AndroidRuntime( 7876): at android.view.View.draw(View.java:15618) E/AndroidRuntime( 7876): at android.view.View.updateDisplayListIfDirty(View.java:14495) E/AndroidRuntime( 7876): at android.view.View.getDisplayList(View.java:14524) ...为了解决这个问题，我们需要override RecyclerView的attachLayoutAnimationParameters方法：
package com.github.nuptboyzhb.recyclerviewanimation.grid; import android.content.Context; import android.support.annotation.Nullable; import android.support.v7.widget.GridLayoutManager; import android.support.v7.widget.RecyclerView; import android.support.v7.widget.StaggeredGridLayoutManager; import android.util.AttributeSet; import android.view.View; import android.view.ViewGroup; import android.view.animation.GridLayoutAnimationController; /** * @version Created by haibozheng on 2016/12/9. * @Author Zheng Haibo * @Blog github.com/nuptboyzhb * @Company Alibaba Group * @Description StaggeredGridRecyclerView */ public class StaggeredGridRecyclerView extends RecyclerView { public StaggeredGridRecyclerView(Context context) { super(context); } public StaggeredGridRecyclerView(Context context, @Nullable AttributeSet attrs) { super(context, attrs); } public StaggeredGridRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); } /** * 支持GridLayoutManager以及StaggeredGridLayoutManager * * @param child * @param params * @param index * @param count */ @Override protected void attachLayoutAnimationParameters(View child, ViewGroup.LayoutParams params, int index, int count) { LayoutManager layoutManager = this.getLayoutManager(); if (getAdapter() != null && (layoutManager instanceof GridLayoutManager || layoutManager instanceof StaggeredGridLayoutManager)) { GridLayoutAnimationController.AnimationParameters animationParams = (GridLayoutAnimationController.AnimationParameters) params.layoutAnimationParameters; if (animationParams == null) { animationParams = new GridLayoutAnimationController.AnimationParameters(); params.layoutAnimationParameters = animationParams; } int columns = 0; if (layoutManager instanceof GridLayoutManager) { columns = ((GridLayoutManager) layoutManager).getSpanCount(); } else { columns = ((StaggeredGridLayoutManager) layoutManager).getSpanCount(); } animationParams.count = count; animationParams.index = index; animationParams.columnsCount = columns; animationParams.rowsCount = count / columns; final int invertedIndex = count - 1 - index; animationParams.column = columns - 1 - (invertedIndex % columns); animationParams.row = animationParams.rowsCount - 1 - invertedIndex / columns; } else { super.attachLayoutAnimationParameters(child, params, index, count); } } }更多动画效果，请参见Github源码：https://github.com/nuptboyzhb/RecyclerViewAnimation
通过LayoutAnimationController或者GridLayoutAnimationController来实现RecyclerView的动画，非常简单，而且效果很好。该方式不仅可以应用于RecyclerView，而且还适用于ListView、LinearLayout、GridView等ViewGroup。比如，如下是作用在一个LinearLayout的效果。
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