67.源码解析：Picasso

1.使用

Picasso.with(context)        .load(url)        .into(imageView);

2.源码解析

1. 先使用Picasso.Builder生成一个单例Picasso
2. load的时候生成一个RequestCreator
3. into的时候由RequestCreator生成一个Request,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，Future获取结果
6. BitmapHunter根据Action获取图片后，将结果交给Diapatcher
7. Dispatcher通知Picasso执行complete
8. Picasso调用Action.complete()方法

（1）先使用Picasso.Builder生成一个单例Picasso

Picasso.with--->Bulider.build--->new Picasso(……),这里使用了单例模式和建造者模式

public static Picasso with(Context context) {if (singleton == null) {synchronized (Picasso.class) {if (singleton == null) {singleton = new Builder(context).build();}    }  }return singleton;}

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);}}

Picasso(Context context, Dispatcher dispatcher, Cache cache, Listener listener,RequestTransformer requestTransformer, List<RequestHandler> extraRequestHandlers, Stats stats,Bitmap.Config defaultBitmapConfig, boolean indicatorsEnabled, boolean loggingEnabled) {this.context = context;  this.dispatcher = dispatcher;  this.cache = cache;  this.listener = listener;  this.requestTransformer = requestTransformer;  this.defaultBitmapConfig = defaultBitmapConfig;

int builtInHandlers = 7; // Adjust this as internal handlers are added or removed.int extraCount = (extraRequestHandlers != null ? extraRequestHandlers.size() : 0);List<RequestHandler> allRequestHandlers =new ArrayList<RequestHandler>(builtInHandlers + extraCount);

// ResourceRequestHandler needs to be the first in the list to avoid  // forcing other RequestHandlers to perform null checks on request.uri  // to cover the (request.resourceId != 0) case.allRequestHandlers.add(new ResourceRequestHandler(context));  if (extraRequestHandlers != null) {    allRequestHandlers.addAll(extraRequestHandlers);}  allRequestHandlers.add(new ContactsPhotoRequestHandler(context));allRequestHandlers.add(new MediaStoreRequestHandler(context));allRequestHandlers.add(new ContentStreamRequestHandler(context));allRequestHandlers.add(new AssetRequestHandler(context));allRequestHandlers.add(new FileRequestHandler(context));allRequestHandlers.add(new NetworkRequestHandler(dispatcher.downloader, stats));requestHandlers = Collections.unmodifiableList(allRequestHandlers);

this.stats = stats;  this.targetToAction = new WeakHashMap<Object, Action>();  this.targetToDeferredRequestCreator = new WeakHashMap<ImageView, DeferredRequestCreator>();  this.indicatorsEnabled = indicatorsEnabled;  this.loggingEnabled = loggingEnabled;  this.referenceQueue = new ReferenceQueue<Object>();  this.cleanupThread = new CleanupThread(referenceQueue, HANDLER);  this.cleanupThread.start();}

（2）load的时候生成一个RequestCreator

picasso.load()--->new RequestCreator()

public RequestCreator load(String path) {if (path == null) {return new RequestCreator(this, null, 0);}if (path.trim().length() == 0) {throw new IllegalArgumentException("Path must not be empty.");}return load(Uri.parse(path));}

public RequestCreator load(Uri uri) {return new RequestCreator(this, uri, 0);}

RequestCreator(Picasso picasso, Uri uri, int resourceId) {if (picasso.shutdown) {throw new IllegalStateException("Picasso instance already shut down. Cannot submit new requests.");}this.picasso = picasso;  this.data = new Request.Builder(uri, resourceId, picasso.defaultBitmapConfig);}

（3）into的时候由RequestCreator生成一个Request,再将Request和Target组合成Action

这里,Dispatcher做为任务分发器，存在着两个Handler：

this.handler = new DispatcherHandler(dispatcherThread.getLooper(), this);//后台线程的Handler

this.mainThreadHandler = mainThreadHandler;//主线程的Handler

public void into(ImageView target) {  into(target, null);}

public void into(ImageView target, Callback callback) {long started = System.nanoTime();checkMain();

if (target == null) {throw new IllegalArgumentException("Target must not be null.");}

if (!data.hasImage()) {picasso.cancelRequest(target);    if (setPlaceholder) {setPlaceholder(target, getPlaceholderDrawable());}return;}

if (deferred) {if (data.hasSize()) {throw new IllegalStateException("Fit cannot be used with resize.");}int width = target.getWidth();    int height = target.getHeight();    if (width == 0 || height == 0) {if (setPlaceholder) {setPlaceholder(target, getPlaceholderDrawable());}picasso.defer(target, new DeferredRequestCreator(this, target, callback));      return;}data.resize(width, height);}

Request request = createRequest(started);String requestKey = createKey(request);

if (shouldReadFromMemoryCache(memoryPolicy)) {    Bitmap bitmap = picasso.quickMemoryCacheCheck(requestKey);    if (bitmap != null) {picasso.cancelRequest(target);setBitmap(target, picasso.context, bitmap, MEMORY, noFade, picasso.indicatorsEnabled);      if (picasso.loggingEnabled) {log(OWNER_MAIN, VERB_COMPLETED, request.plainId(), "from " + MEMORY);}if (callback != null) {        callback.onSuccess();}return;}  }

if (setPlaceholder) {setPlaceholder(target, getPlaceholderDrawable());}

Action action =new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId,errorDrawable, requestKey, tag, callback, noFade);

picasso.enqueueAndSubmit(action);}

（4）由Picasso交给Dispatcher后台执行

void enqueueAndSubmit(Action action) {  Object target = action.getTarget();  if (target != null && targetToAction.get(target) != action) {// This will also check we are on the main thread.cancelExistingRequest(target);targetToAction.put(target, action);}  submit(action);}

void submit(Action action) {dispatcher.dispatchSubmit(action);}

（5）Dispatcher用Action生成BitmapHunter，交于PicassoExecutorService执行，Future获取结果

void dispatchSubmit(Action action) {handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action));}

@Override public void handleMessage(final Message msg) {switch (msg.what) {case REQUEST_SUBMIT: {      Action action = (Action) msg.obj;dispatcher.performSubmit(action);      break;}

dispatchSubmit运行在主线程上，通过Handle传递之后，performSubmit已经运行在dispatcherThread线程上

void performSubmit(Action action) {  performSubmit(action, true);}

void performSubmit(Action action, boolean dismissFailed) {if (pausedTags.contains(action.getTag())) {pausedActions.put(action.getTarget(), action);    if (action.getPicasso().loggingEnabled) {log(OWNER_DISPATCHER, VERB_PAUSED, action.request.logId(),"because tag ‘" + action.getTag() + "‘ is paused");}return;}

BitmapHunter hunter = hunterMap.get(action.getKey());  if (hunter != null) {    hunter.attach(action);    return;}

if (service.isShutdown()) {if (action.getPicasso().loggingEnabled) {log(OWNER_DISPATCHER, VERB_IGNORED, action.request.logId(), "because shut down");}return;}

hunter = forRequest(action.getPicasso(), this, cache, stats, action);hunter.future = service.submit(hunter);hunterMap.put(action.getKey(), hunter);  if (dismissFailed) {failedActions.remove(action.getTarget());}

if (action.getPicasso().loggingEnabled) {log(OWNER_DISPATCHER, VERB_ENQUEUED, action.request.logId());}}

（6）BitmapHunter根据Action获取图片后，将结果交给Diapatcher

static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats,Action action) {  Request request = action.getRequest();List<RequestHandler> requestHandlers = picasso.getRequestHandlers();

// Index-based loop to avoid allocating an iterator.  //noinspection ForLoopReplaceableByForEachfor (int i = 0, count = requestHandlers.size(); i < count; i++) {    RequestHandler requestHandler = requestHandlers.get(i);    if (requestHandler.canHandleRequest(request)) {return new BitmapHunter(picasso, dispatcher, cache, stats, action, requestHandler);}  }

return new BitmapHunter(picasso, dispatcher, cache, stats, action, ERRORING_HANDLER);}

BitmapHunter为后台执行下载的线程，继承了Runnable

@Override public void run() {try {updateThreadName(data);

if (picasso.loggingEnabled) {log(OWNER_HUNTER, VERB_EXECUTING, getLogIdsForHunter(this));}

result = hunt();

if (result == null) {dispatcher.dispatchFailed(this);} else {dispatcher.dispatchComplete(this);}  } catch (Downloader.ResponseException e) {if (!e.localCacheOnly || e.responseCode != 504) {exception = e;}dispatcher.dispatchFailed(this);} catch (NetworkRequestHandler.ContentLengthException e) {exception = e;dispatcher.dispatchRetry(this);} catch (IOException e) {exception = e;dispatcher.dispatchRetry(this);} catch (OutOfMemoryError e) {    StringWriter writer = new StringWriter();stats.createSnapshot().dump(new PrintWriter(writer));exception = new RuntimeException(writer.toString(), e);dispatcher.dispatchFailed(this);} catch (Exception e) {exception = e;dispatcher.dispatchFailed(this);} finally {    Thread.currentThread().setName(Utils.THREAD_IDLE_NAME);}}

获取图片的主要逻辑

Bitmap hunt() throws IOException {  Bitmap bitmap = null;

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;}  }

data.networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy;RequestHandler.Result result = requestHandler.load(data, networkPolicy);  if (result != null) {loadedFrom = result.getLoadedFrom();exifOrientation = result.getExifOrientation();bitmap = result.getBitmap();

// If there was no Bitmap then we need to decode it from the stream.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);    if (data.needsTransformation() || exifOrientation != 0) {synchronized (DECODE_LOCK) {if (data.needsMatrixTransform() || exifOrientation != 0) {          bitmap = transformResult(data, bitmap, exifOrientation);          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;}

（7）Diapatcher添加缓存，通知Picasso执行complete

void dispatchComplete(BitmapHunter hunter) {handler.sendMessage(handler.obtainMessage(HUNTER_COMPLETE, hunter));}

case HUNTER_COMPLETE: {  BitmapHunter hunter = (BitmapHunter) msg.obj;dispatcher.performComplete(hunter);  break;}

下载完成后，添加进缓存

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");}}

private void batch(BitmapHunter hunter) {if (hunter.isCancelled()) {return;}batch.add(hunter);  if (!handler.hasMessages(HUNTER_DELAY_NEXT_BATCH)) {handler.sendEmptyMessageDelayed(HUNTER_DELAY_NEXT_BATCH, BATCH_DELAY);}}

case HUNTER_DELAY_NEXT_BATCH: {dispatcher.performBatchComplete();  break;}

void performBatchComplete() {  List<BitmapHunter> copy = new ArrayList<BitmapHunter>(batch);batch.clear();mainThreadHandler.sendMessage(mainThreadHandler.obtainMessage(HUNTER_BATCH_COMPLETE, copy));logBatch(copy);}

（8）Picasso调用Action.complete()方法，显示图片

static final Handler HANDLER = new Handler(Looper.getMainLooper()) {@Override public void handleMessage(Message msg) {switch (msg.what) {case HUNTER_BATCH_COMPLETE: {@SuppressWarnings("unchecked") List<BitmapHunter> batch = (List<BitmapHunter>) msg.obj;//noinspection ForLoopReplaceableByForEachfor (int i = 0, n = batch.size(); i < n; i++) {          BitmapHunter hunter = batch.get(i);hunter.picasso.complete(hunter);}break;}

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 ForLoopReplaceableByForEachfor (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);}}

private void deliverAction(Bitmap result, LoadedFrom from, Action action) {if (action.isCancelled()) {return;}if (!action.willReplay()) {targetToAction.remove(action.getTarget());}if (result != null) {if (from == null) {throw new AssertionError("LoadedFrom cannot be null.");}    action.complete(result, from);    if (loggingEnabled) {log(OWNER_MAIN, VERB_COMPLETED, action.request.logId(), "from " + from);}  } else {    action.error();    if (loggingEnabled) {log(OWNER_MAIN, VERB_ERRORED, action.request.logId());}  }}

ImageViewAction,继承至Action

@Override public void complete(Bitmap result, Picasso.LoadedFrom from) {if (result == null) {throw new AssertionError(        String.format("Attempted to complete action with no result!\n%s", this));}

ImageView target = this.target.get();  if (target == null) {return;}

Context context = picasso.context;  boolean indicatorsEnabled = picasso.indicatorsEnabled;PicassoDrawable.setBitmap(target, context, result, from, noFade, indicatorsEnabled);

if (callback != null) {callback.onSuccess();}}

static void setBitmap(ImageView target, Context context, Bitmap bitmap,Picasso.LoadedFrom loadedFrom, boolean noFade, boolean debugging) {  Drawable placeholder = target.getDrawable();  if (placeholder instanceof AnimationDrawable) {    ((AnimationDrawable) placeholder).stop();}  PicassoDrawable drawable =new PicassoDrawable(context, bitmap, placeholder, loadedFrom, noFade, debugging);target.setImageDrawable(drawable);}

参考：

http://blog.csdn.net/qq373432361/article/details/44495305

http://caij.github.io/android/2015/09/11/Picasso源码解析/

http://www.devdiv.com/android_squareup_picasso_-blog-32103-57174.html

http://www.mamicode.com/info-detail-623596.html

来自为知笔记(Wiz)