为ViewGroup添加入场动画，LayoutAnimation使用概述

本篇文章来一点好玩的效果。还记得之前的视图动画效果吗？之前我们控制的效果，都是针对单个视图，如果想要对一组视图使用相同的动画效果，这个时候，就需要使用到LayoutAnimationController了。

LayoutAnimationController介绍：

Android Developer LayoutAnimationController docment

• LayoutAnimationController用于为一个layout里面的控件，或者是一个ViewGroup里面的控件设置动画效果（即整个布局）
• 每一个控件都有相同的动画效果
• 这些控件的动画效果可在不同的时间显示出来

LayoutAnimationController的使用非常简单

xml直接使用

<layoutAnimation xmlns:android="http://schemas.android.com/apk/res/android"android:delay="0.1"  //表示动画播放的延时，既可以是百分比，也可以是float小数。android:animationOrder="reverse" //表示动画的播放顺序，//有三个取值normal(顺序)、reverse(反序)、random(随机)。android:animation="@anim/animation"  //指向了子控件所要播放的动画/>

然后将定义好的动画配置到ViewGroup的布局中即可。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/llViewGroupContainer"android:layout_width="match_parent"android:layout_height="match_parent"android:layoutAnimation="@anim/list_anim_layout"android:background="@android:color/white"android:orientation="vertical"><TextView...
</LinearLayout>    

代码中配置使用

val layoutAnimationController =LayoutAnimationController(LayoutAnimationHelper.getAnimationSetFromRight())layoutAnimationController.delay= 0.1FlayoutAnimationController.order = LayoutAnimationController.ORDER_NORMALllViewGroupContainer.layoutAnimation = layoutAnimationControllerllViewGroupContainer.scheduleLayoutAnimation()

/*** 从右侧进入，并带有弹性的动画** @return*/
public static AnimationSet getAnimationSetFromRight() {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);AlphaAnimation alphaAnimation = new AlphaAnimation(0.5f, 1.0f);alphaAnimation.setDuration(400);alphaAnimation.setInterpolator(new AccelerateDecelerateInterpolator());animationSet.addAnimation(translateX1);animationSet.addAnimation(translateX2);animationSet.addAnimation(translateX3);animationSet.addAnimation(alphaAnimation);animationSet.setDuration(400);return animationSet;
}

下面是效果

为了让大家看的时候更清晰效果，所以视频做了慢放处理，可以看到是有回弹会效果的，还是比较炫酷的。如果是recyclerView，也可以使用LayoutAnimationController来实现类似效果。

//为RecyclerView添加动画
val layoutAnimationController =LayoutAnimationController(LayoutAnimationHelper.getAnimationSetFromRight())
layoutAnimationController.delay = 0.1F
layoutAnimationController.order = LayoutAnimationController.ORDER_NORMALrvContentList.layoutAnimation = layoutAnimationController

可以看到动画的执行顺序是顺序执行的，ViewGroup和RecyclerView中，都是顺序执行的，但是如果现在是GridView或者RecylcerView#GridLayoutManager方式，我们可能希望沿着对角线方向实现动画效果，而不是一个个来。则需要进行自定义动画的执行方向。LayoutAnimationController动画执行方向修改也很简单，只需要重写ViewGroup#protected void attachLayoutAnimationParameters(View child, LayoutParams params, int index, int count)方法即可。

下面是对于RecycleView#GridLayoutManager实现对角线方向动画效果的代码

public class GridRecyclerView extends RecyclerView {/** @see View#View(Context) */public GridRecyclerView(Context context) { super(context); }/** @see View#View(Context, AttributeSet) */public GridRecyclerView(Context context, AttributeSet attrs) { super(context, attrs); }/** @see View#View(Context, AttributeSet, int) */public GridRecyclerView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); }@Overrideprotected void attachLayoutAnimationParameters(View child, ViewGroup.LayoutParams params,int index, int count) {final LayoutManager layoutManager = getLayoutManager();if (getAdapter() != null && layoutManager instanceof GridLayoutManager){GridLayoutAnimationController.AnimationParameters animationParams =(GridLayoutAnimationController.AnimationParameters) params.layoutAnimationParameters;if (animationParams == null) {// If there are no animation parameters, create new once and attach them to// the LayoutParams.animationParams = new GridLayoutAnimationController.AnimationParameters();params.layoutAnimationParameters = animationParams;}// Next we are updating the parameters// Set the number of items in the RecyclerView and the index of this itemanimationParams.count = count;animationParams.index = index;// Calculate the number of columns and rows in the gridfinal int columns = ((GridLayoutManager) layoutManager).getSpanCount();animationParams.columnsCount = columns;animationParams.rowsCount = count / columns;// Calculate the column/row position in the gridfinal int invertedIndex = count - 1 - index;animationParams.column = columns - 1 - (invertedIndex % columns);animationParams.row = animationParams.rowsCount - 1 - invertedIndex / columns;} else {// Proceed as normal if using another type of LayoutManagersuper.attachLayoutAnimationParameters(child, params, index, count);}}
}

使用上和之前使用没有任何区别。下面来看下效果。动画执行顺序还是区别很明显的。