Picasso源码分析4

0使用手册

http://square.github.io/picasso/

1使用方法简介

Picasso.with(context) 
.load(url) 
.resize(50, 50) 
.centerCrop() 
.into(imageView)

2 基本原理

1. 先使用Picasso.Builder生成一个单例Picasso，
2. load的时候生成一个RequestCreator，再设置不同的Reqeust参数，into的时候生成一个Request，
3. 再将Request和Target组合成Action，
4. 由Picasso交给Dispatcher后台执行，
5. Dispatcher用Action生成BitmapHunter，交于PicassoExecutorService执行，BitmapHunter下载完成，执行相应的变换后，
6. 用Handler通知Dispatcher缓存在内存中，
7. Dispatcher再用Handler通知Picasso调用Action.complete()方法

3数据结构分析

RequestHandler: 根据Request获取相应的内容。FileRequestHandler使用ContentResolver从文件中获取。NetworkRequestHandler使用Downloader从网络获取。ResourceRequestHandler从apk资源中获取。ContactsPhotoRequestHandler使用ContentResolver从通讯录中获取。ContentStreamRequestHandler使用ContentResolver获取。

Downloader： 从网络获取时需要下载。UrlConnectionDownloader使用UrlConnection从网络下载，HttpResponseCache可以让UrlConnection使用文件缓存数据。OkHttpDownloader使用OkHttp库来下载图片，OkHttpClient.setCache可以让OkHttp使用文件缓存

Stats：统计数据，缓存的命中率等等

Action：包含Request，Target和PlaceHolder，和异步加载后的回调，complete，error，cancel。

BitmapHunter： 异步Runnable任务。

4源代码分析

1. Picasso.Builder.build()

 /** 2. 构造Picasso,使用Picasso.with会构造默认的方法，如果要自定义Picasso，则需要使用Builder，并在构造好了 3. 之后使用Picasso.setSingletonInstance.   *//** Create the {@link Picasso} instance. */    public Picasso build() {      Context context = this.context;      if (downloader == null) {        downloader = Utils.createDefaultDownloader(context);      }      if (cache == null) {        cache = new LruCache(context);      }      if (service == null) {        service = new PicassoExecutorService();      }      if (transformer == null) {        transformer = RequestTransformer.IDENTITY;      }      Stats stats = new Stats(cache);      Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);      return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,          defaultBitmapConfig, indicatorsEnabled, loggingEnabled);    }
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1. RequestCreator.into()

 /**     * 调用into方法时，使用Request.Builder创建一个Request，然后交给Dispatcher调度执行。     * @param target     */  public void into(Target target) {    long started = System.nanoTime();    checkMain();    if (target == null) {      throw new IllegalArgumentException("Target must not be null.");    }    //当target是ImageView时，需要deferred，生成DeferredRequestCreator,利用ImageView的addOnPreDrawListener()当需要绘制的时候再来进行加载    if (deferred) {      throw new IllegalStateException("Fit cannot be used with a Target.");    }      //url为空或者resourceid为空，直接Cancel    if (!data.hasImage()) {      picasso.cancelRequest(target);      target.onPrepareLoad(setPlaceholder ? getPlaceholderDrawable() : null);      return;    }    Request request = createRequest(started);    String requestKey = createKey(request);    if (shouldReadFromMemoryCache(memoryPolicy)) {      Bitmap bitmap = picasso.quickMemoryCacheCheck(requestKey);      if (bitmap != null) {        picasso.cancelRequest(target);        target.onBitmapLoaded(bitmap, MEMORY);        return;      }    }    target.onPrepareLoad(setPlaceholder ? getPlaceholderDrawable() : null);    Action action =        new TargetAction(picasso, target, request, memoryPolicy, networkPolicy, errorDrawable,            requestKey, tag, errorResId);    picasso.enqueueAndSubmit(action);  }
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1. BitmapHunter.hunt()

  Bitmap hunt() throws IOException {    Bitmap bitmap = null;    //判断是否从内存加载    if (shouldReadFromMemoryCache(memoryPolicy)) {      bitmap = cache.get(key);      if (bitmap != null) {        stats.dispatchCacheHit();        loadedFrom = MEMORY;        if (picasso.loggingEnabled) {          log(OWNER_HUNTER, VERB_DECODED, data.logId(), "from cache");        }        return bitmap;      }    }      //使用RequestHandler加载图片    data.networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy;    RequestHandler.Result result = requestHandler.load(data, networkPolicy);    if (result != null) {      loadedFrom = result.getLoadedFrom();      exifRotation = result.getExifOrientation();      bitmap = result.getBitmap();      //如果得到的不是图片而是InputStream，则转换成Bitmap      if (bitmap == null) {        InputStream is = result.getStream();        try {          bitmap = decodeStream(is, data);        } finally {          Utils.closeQuietly(is);        }      }    }    if (bitmap != null) {      if (picasso.loggingEnabled) {        log(OWNER_HUNTER, VERB_DECODED, data.logId());      }      stats.dispatchBitmapDecoded(bitmap);        //进行裁剪，旋转等变换      if (data.needsTransformation() || exifRotation != 0) {        synchronized (DECODE_LOCK) {          if (data.needsMatrixTransform() || exifRotation != 0) {            bitmap = transformResult(data, bitmap, exifRotation);            if (picasso.loggingEnabled) {              log(OWNER_HUNTER, VERB_TRANSFORMED, data.logId());            }          }          if (data.hasCustomTransformations()) {            bitmap = applyCustomTransformations(data.transformations, bitmap);            if (picasso.loggingEnabled) {              log(OWNER_HUNTER, VERB_TRANSFORMED, data.logId(), "from custom transformations");            }          }        }        if (bitmap != null) {          stats.dispatchBitmapTransformed(bitmap);        }      }    }    return bitmap;  }
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1. Dispatcher.performComplete()

//先判断是否要写内存缓存，然后将当前的hunter批量。  //批量的原因是在Picasso的Handler当前可能还有没有处理的。再Dispatcher这一级别再缓冲一下  void performComplete(BitmapHunter hunter) {    if (shouldWriteToMemoryCache(hunter.getMemoryPolicy())) {      cache.set(hunter.getKey(), hunter.getResult());    }    hunterMap.remove(hunter.getKey());    batch(hunter);    if (hunter.getPicasso().loggingEnabled) {      log(OWNER_DISPATCHER, VERB_BATCHED, getLogIdsForHunter(hunter), "for completion");    }  }
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1. Picasso.comple()

//从Hunter中取出结果，调用Action.complete，or Action.error  void complete(BitmapHunter hunter) {    Action single = hunter.getAction();    List<Action> joined = hunter.getActions();    boolean hasMultiple = joined != null && !joined.isEmpty();    boolean shouldDeliver = single != null || hasMultiple;    if (!shouldDeliver) {      return;    }    Uri uri = hunter.getData().uri;    Exception exception = hunter.getException();    Bitmap result = hunter.getResult();    LoadedFrom from = hunter.getLoadedFrom();    if (single != null) {      deliverAction(result, from, single);    }    if (hasMultiple) {      //noinspection ForLoopReplaceableByForEach      for (int i = 0, n = joined.size(); i < n; i++) {        Action join = joined.get(i);        deliverAction(result, from, join);      }    }    if (listener != null && exception != null) {      listener.onImageLoadFailed(this, uri, exception);    }  }
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