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.LottieAnimationView        android: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() {            @Override            public 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() {            @Override            public 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.LottieAnimationView        android: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.LottieAnimationView        android:id="@+id/lottie_anim"        android:layout_width="wrap_content"        android:layout_height="wrap_content"         />  <Button    android: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 @Override    public 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0        mLottieAnim.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;        }        @Override        protected LottieComposition doInBackground(InputStream... params) {            return fromInputStream(res, params[0]);        }        @Override        protected 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 {        @Override        public 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 ResultOfMethodCallIgnored            file.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() {            @Override            public 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