Lottie动画框架入门及源码简析

现在越来越多的APP中添加动画来提升用户体验，下面简单介绍下Airbnb开源的动画框架Lottie的使用

一、基本使用

首先添加依赖
compile ‘com.airbnb.android:lottie:1.0.1’

方法一：

1、xml文件中添加布局文件

 <com.airbnb.lottie.LottieAnimationViewandroid:id="@+id/lottie_anim"android:layout_width="wrap_content"android:layout_height="wrap_content"/>

2、Activity中对动画进行控制，注释写的很清楚了

//初始化控件
LottieAnimationView mLottieAnimView= (LottieAnimationView) findViewById(R.id.lottie_anim);/***  添加json格式文件从assets中导入*  第一个参数：Context*  第二个参数：动画文件*  第三个参数：动画数据监听*/LottieComposition.fromAssetFileName(this, "LottieLogo.json", new LottieComposition.OnCompositionLoadedListener() {@Overridepublic void onCompositionLoaded(LottieComposition composition) {//设置动画数据mLottieAnimView.setComposition(composition);//播放动画mLottieAnimView.playAnimation();//设置循环mLottieAnimView.loop(true);}});// 设置动画监听mLottieAnimView.addAnimatorUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {}});}

直接运行程序动画就开始播放了

方法二

1、直接通过XML布局文件控制动画，不通过Activity进行操作

<com.airbnb.lottie.LottieAnimationViewandroid:id="@+id/lottie_anim"android:layout_width="wrap_content"android:layout_height="wrap_content"app:lottie_fileName="LottieLogo.json"app:lottie_autoPlay="true"app:lottie_loop="true"/>

属性说明：

//指定动画文件名
app:lottie_fileName=”“

//设置自动播放 true/false
app:lottie_autoPlay=”true”

//设置动画是否循环 true/false
app:lottie_loop=”true”

接下来直接运行项目即可

方法三

1、xml文件中添加布局文件

 <com.airbnb.lottie.LottieAnimationViewandroid:id="@+id/lottie_anim"android:layout_width="wrap_content"android:layout_height="wrap_content"/><Buttonandroid:id="@+id/btn_start"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="开始"/>

2、通过在Activity中按钮来控制动画播放

 mLottieAnim = (LottieAnimationView) findViewById(R.id.lottie_anim);Button mBtnStart= (Button) findViewById(R.id.btn_start);mBtnStart.setOnClickListener(this);//通过直接指定动画名的方式设置动画mLottieAnim.setAnimation("LottieLogo.json");//点击后播放@Overridepublic void onClick(View v) {//判断动画是否在播放if (!mLottieAnim.isAnimating()){//设置进度mLottieAnim.setProgress(0);//开始播放动画mLottieAnim.playAnimation();}}

OK，简单使用介绍完毕

二、常用API

        // 判断动画是否正在播放中mLottieAnim.isAnimating()//设置动画数据  可以接收json格式数据  String格式 、Animation格式mLottieAnim.setAnimation();//播放动画mLottieAnim.playAnimation();//暂停动画mLottieAnim.pauseAnimation();//取消动画mLottieAnim.cancelAnimation();//获取动画时长，一定要在动画开始播放后才能获取否则为0mLottieAnim.getDuration();// 设置动画更新监听mLottieAnim.addAnimatorUpdateListener();//移除动画更新监听mLottieAnim.removeUpdateListener();//动画监听，可以用于监听动画的开始、结束、取消、重复mLottieAnim.addAnimatorListener();// 移除动画监听mLottieAnim.removeAnimatorListener();// 设置合成物  LottieComposition类型mLottieAnim.setComposition();// 设置循环mLottieAnim.loop();// 添加assets中动画文件LottieComposition.fromAssetFileName()// 使用同步方式接收动画文件LottieComposition.fromFileSync();// 添加json格式动画文件LottieComposition.fromJson()// 使用同步方式接收json格式文件LottieComposition.fromJsonSync()// 接收流的形式动画LottieComposition.fromInputStream()

三、源码分析

由简到难，一步步分析

1、类LottieComposition中方法

A: 加载assets中文件

/*** Loads a composition from a file stored in /assets.*/public static Cancellable fromAssetFileName(Context context, String fileName, OnCompositionLoadedListener loadedListener) {InputStream stream;try {stream = context.getAssets().open(fileName);} catch (IOException e) {throw new IllegalStateException("Unable to find file " + fileName, e);}return fromInputStream(context, stream, loadedListener);}

可以看到通过读取assets中文件返回一个流格式，直接跳到fromInputStream（）方法

B:接下来我们查看fromInputStream（）方法

 /*** Loads a composition from an arbitrary input stream.** ex: fromInputStream(context, new FileInputStream(filePath), (composition) -> {});*/public static Cancellable fromInputStream(Context context, InputStream stream, OnCompositionLoadedListener loadedListener) {FileCompositionLoader loader = new FileCompositionLoader(context.getResources(), loadedListener);loader.execute(stream);return loader;}

通过上面代码我们发现直接通过FileCompositionLoader来执行流文件 loader.execute(stream);

C:查看FileCompositionLoader

private static final class FileCompositionLoader extends CompositionLoader<InputStream> {private final Resources res;private final OnCompositionLoadedListener loadedListener;FileCompositionLoader(Resources res, OnCompositionLoadedListener loadedListener) {this.res = res;this.loadedListener = loadedListener;}@Overrideprotected LottieComposition doInBackground(InputStream... params) {return fromInputStream(res, params[0]);}@Overrideprotected void onPostExecute(LottieComposition composition) {loadedListener.onCompositionLoaded(composition);}}

发现FileCompositionLoader继承CompositionLoader，并且在doInBackground()方法中返回了方法
fromInputStream(res, params[0]);

D:查看CompositionLoader

  private abstract static class CompositionLoader<Params>extends AsyncTask<Params, Void, LottieComposition>implements Cancellable {@Overridepublic void cancel() {cancel(true);}}

CompositionLoader继承了AsyncTask可见该类是采用异步执行的方式加载流

E:fromInputStream(res, params[0])
C中我们发现在方法doInBackground()中异步执行了该方法，继续分析

 @SuppressWarnings("WeakerAccess")public static LottieComposition fromInputStream(Resources res, InputStream file) {try {int size = file.available();byte[] buffer = new byte[size];//noinspection ResultOfMethodCallIgnoredfile.read(buffer);file.close();String json = new String(buffer, "UTF-8");JSONObject jsonObject = new JSONObject(json);return LottieComposition.fromJsonSync(res,jsonObject);} catch (IOException e) {throw new IllegalStateException("Unable to find file.", e);} catch (JSONException e) {throw new IllegalStateException("Unable to load JSON.", e);}}

通过查看发现该方法将数据转化成json格式并返回给LottieComposition.fromJsonSync(res,jsonObject)方法执行，可见fromJsonSync对json数据进行了解析操作

F:继续跟进方法

@SuppressWarnings("WeakerAccess")public static LottieComposition fromJsonSync(Resources res, JSONObject json) {LottieComposition composition = new LottieComposition(res);int width = -1;int height = -1;try {width = json.getInt("w");height = json.getInt("h");} catch (JSONException e) {// ignore.}if (width != -1 && height != -1) {int scaledWidth = (int) (width * composition.scale);int scaledHeight = (int) (height * composition.scale);if (Math.max(scaledWidth, scaledHeight) > MAX_PIXELS) {float factor = (float) MAX_PIXELS / (float) Math.max(scaledWidth, scaledHeight);scaledWidth *= factor;scaledHeight *= factor;composition.scale *= factor;}composition.bounds = new Rect(0, 0, scaledWidth, scaledHeight);}try {composition.startFrame = json.getLong("ip");composition.endFrame = json.getLong("op");composition.frameRate = json.getInt("fr");} catch (JSONException e) {//}if (composition.endFrame != 0 && composition.frameRate != 0) {long frameDuration = composition.endFrame - composition.startFrame;composition.duration = (long) (frameDuration / (float) composition.frameRate * 1000);}try {JSONArray jsonLayers = json.getJSONArray("layers");for (int i = 0; i < jsonLayers.length(); i++) {Layer layer = Layer.fromJson(jsonLayers.getJSONObject(i), composition);addLayer(composition, layer);}} catch (JSONException e) {throw new IllegalStateException("Unable to find layers.", e);}// These are precomps. This naively adds the precomp layers to the main composition.// TODO: Significant work will have to be done to properly support them.try {JSONArray assets = json.getJSONArray("assets");for (int i = 0; i < assets.length(); i++) {JSONObject asset = assets.getJSONObject(i);JSONArray layers = asset.getJSONArray("layers");for (int j = 0; j < layers.length(); j++) {Layer layer = Layer.fromJson(layers.getJSONObject(j), composition);addLayer(composition, layer);}}} catch (JSONException e) {// Do nothing.}return composition;}

通过查看方法，方法中对json格式数据进行了解析并且通过 LottieComposition composition对象进行了接收并且调用了Layer.fromJson和addLayer(composition, layer);方法

G:查看Layer.fromJson及addLayer(composition, layer);

通过fromJson()方法将json数据解析并赋值给layer

 static Layer fromJson(JSONObject json, LottieComposition composition) {Layer layer = new Layer(composition);try {if (L.DBG) Log.d(TAG, "Parsing new layer.");layer.layerName = json.getString("nm");if (L.DBG) Log.d(TAG, "\tName=" + layer.layerName);layer.layerId = json.getLong("ind");if (L.DBG) Log.d(TAG, "\tId=" + layer.layerId);layer.frameRate = composition.getFrameRate();int layerType = json.getInt("ty");if (layerType <= LottieLayerType.Shape.ordinal()) {layer.layerType = LottieLayerType.values()[layerType];} else {layer.layerType = LottieLayerType.Unknown;}.....省略代码段return layer;

通过addLayer方法将解析出来的json数据Layer添加到composition.layers中
可以将composition理解为一个包含图层信息的对象

 private static void addLayer(LottieComposition composition, Layer layer) {composition.layers.add(layer);composition.layerMap.put(layer.getId(), layer);if (!layer.getMasks().isEmpty()) {composition.hasMasks = true;}if (layer.getMatteType() != null && layer.getMatteType() != Layer.MatteType.None) {composition.hasMattes = true;}}

H:通过以上的分析我们只发现了composition对象存储了解析出来的json信息，下面我们就分析怎样将composition对象转化为动画
接下来查看LottieAnimationView中的setAnimation()方法

  /*** Sets the animation from a file in the assets directory.* This will load and deserialize the file asynchronously.** Will not cache the composition once loaded.*/public void setAnimation(String animationName) {setAnimation(animationName, CacheStrategy.None);}

上面的方法返回setAnimation(animationName, CacheStrategy.None);
那么我们接着查看setAnimation方法做了什么

 @SuppressWarnings("WeakerAccess")public void setAnimation(final String animationName, final CacheStrategy cacheStrategy) {this.animationName = animationName;if (weakRefCache != null && weakRefCache.containsKey(animationName)) {WeakReference<LottieComposition> compRef = weakRefCache.get(animationName);if (compRef.get() != null) {setComposition(compRef.get());return;}} else if (strongRefCache != null && strongRefCache.containsKey(animationName)) {setComposition(strongRefCache.get(animationName));return;}isAnimationLoading = true;setProgressWhenCompositionSet = false;playAnimationWhenCompositionSet = false;this.animationName = animationName;cancelLoaderTask();compositionLoader = LottieComposition.fromAssetFileName(getContext(), animationName, new LottieComposition.OnCompositionLoadedListener() {@Overridepublic void onCompositionLoaded(LottieComposition composition) {if (cacheStrategy == CacheStrategy.Strong) {if (strongRefCache == null) {strongRefCache = new HashMap<>();}strongRefCache.put(animationName, composition);} else if (cacheStrategy == CacheStrategy.Weak) {if (weakRefCache == null) {weakRefCache = new HashMap<>();}weakRefCache.put(animationName, new WeakReference<>(composition));}setComposition(composition);}});}

通过上面的方法我们发现最后调用了 setComposition(composition);
继续分析，查看setComposition(composition);

  public void setComposition(@NonNull LottieComposition composition) {if (L.DBG) {Log.v(TAG, "Set Composition \n" + composition);}lottieDrawable.setCallback(this);lottieDrawable.setComposition(composition);// If you set a different composition on the view, the bounds will not update unless// the drawable is different than the original.setImageDrawable(null);setImageDrawable(lottieDrawable);isAnimationLoading = false;if (setProgressWhenCompositionSet) {setProgressWhenCompositionSet = false;setProgress(progress);} else {setProgress(0f);}this.composition = composition;if (playAnimationWhenCompositionSet) {playAnimationWhenCompositionSet = false;playAnimation();}requestLayout();}

通过上面的分析发现方法 lottieDrawable.setComposition(composition);处理了接收到的composition对象
继续跟踪该方法

 public void setComposition(LottieComposition composition) {if (getCallback() == null) {throw new IllegalStateException("You or your view must set a Drawable.Callback before setting the composition. This gets done automatically when added to an ImageView. " +"Either call ImageView.setImageDrawable() before setComposition() or call setCallback(yourView.getCallback()) first.");}clearComposition();this.composition = composition;animator.setDuration(composition.getDuration());setBounds(0, 0, composition.getBounds().width(), composition.getBounds().height());buildLayersForComposition(composition);getCallback().invalidateDrawable(this);}private void clearComposition() {recycleBitmaps();clearLayers();}

有木有发现一个很熟悉的单词
animator.setDuration(composition.getDuration());
到这里我们终于将composition和动画建立了联系
最终我们发现了下面这个方法
private final ValueAnimator animator = ValueAnimator.ofFloat(0f, 1f);
哈哈，原来是通过ValueAnimator来实现的，好了简单分析了下，就到这里，如有不足，请指正。

参考：http://www.jianshu.com/p/0882ea3b59e3