使用LayoutAnimationController为RecyclerView添加动画

@author:莫川

一、前言

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。

二、效果以及源码

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

Github源码：https://github.com/nuptboyzhb/RecyclerViewAnimation

三、实现方案

(1)LayoutAnimationController

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。

(2)GridLayoutAnimationController

上述方法针对的是线性的RecyclerView，也就是说RecyclerView的LayoutManager设置的是LinearLayoutManager.

    ...@Overrideprotected 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。

    ...@Overrideprotected 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*/@Overrideprotected 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

四、总结

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。