图解Picasso源码
以下是picasso调用的图解:
1.当我们在调用Picasso.with()方法的时候,会生成一个单例的Picasso
public static Picasso with(Context context) { if (singleton == null) { synchronized (Picasso.class) { if (singleton == null) { singleton = new Builder(context).build(); } } } return singleton; }
首先是全局的一个单例对象,其次是通过Builder模式生成对应的Picasso对象。
2.我们在调用完上面的方法之后,会继续调用load方法:
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)); }
支持loadFile,Uri,path等,在这里会其实最终都是调用load(uri)的方法,生成RequestCreator,接下来的placeHolder,errImage,设置图片等,通过链式调用实现。
3.在创建完成RequestCreator之后,我们会执行RequestCreator的into方法:
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()) {//1 picasso.cancelRequest(target); if (setPlaceholder) { setPlaceholder(target, getPlaceholderDrawable()); } return; } if (deferred) { if (data.hasSize()) {//2 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)) {//3 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) {//4 setPlaceholder(target, getPlaceholderDrawable()); } Action action = new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId, errorDrawable, requestKey, tag, callback, noFade); picasso.enqueueAndSubmit(action);//5 }
在这里主要就是执行图片的获取,转换大小以及图片的显示的操作。
3.1 上面的第一步主要是判断有没有资源文件设置或者本地路径等,如果有那么直接显示,这里主要是变相地实现了Picasso的本地图片的加载的实现。
3.2 第二步设置要显示的ImageView控件的大小,以便计算图片和控件的大小比,以进行加载时候内存的优化
3.3 第三步会从内存中去读取图片,读取到图片增加命中的计算器
3.4 第四步是设置空白图片
3.5 第五步主要就是执行图片的获取操作,picasso.enqueueAndSubmit(Action)方法:
4.picasso.enqueueAndSubmit(Action)方法:
void enqueueAndSubmit(Action action) { Object target = action.getTarget();//因为在上面的我们初始化的ImageView的Action,所以target是要加载的ImageView。 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); }
在这里我们会调用submit方法,该方法主要是将action时间分发给对应的Dispatcher,dispatcher.dispatchSubmit(action);
void dispatchSubmit(Action action) { handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action)); }
对应的会通过Handler发送一个REQUEST_SUBMIT的消息,这个Handler是DispatcherHandler的实例对象,执行对应的HandleMessage方法,
case REQUEST_SUBMIT: { Action action = (Action) msg.obj; dispatcher.performSubmit(action); break; }
5.我们来看看Dispatcher类的performSubmit方法:
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);//1 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()); } }
注释1中会一次调用各种RequestHandler的canHandleRequest方法,来选择能处理的RequestHandler
piassco在初始化的时候,默认会添加如下的RequestHandler
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));
6.上述找到对应能处理的RequestHandler之后,创建对应的bitmapHunter,BitmapHunder其实是Runnable的实现。
@Override public Future<?> submit(Runnable task) { PicassoFutureTask ftask = new PicassoFutureTask((BitmapHunter) task); execute(ftask); return ftask; }
创建对应的Runnable完成之后,加入线程池中执行
@Override public void run() { try { updateThreadName(data); if (picasso.loggingEnabled) { log(OWNER_HUNTER, VERB_EXECUTING, getLogIdsForHunter(this)); } result = hunt();//1 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); } }
注释1是获取图片的逻辑
Bitmap hunt() throws IOException { Bitmap bitmap = null; if (shouldReadFromMemoryCache(memoryPolicy)) {//1 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) {//2 loadedFrom = result.getLoadedFrom(); exifRotation = 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) {//3 if (picasso.loggingEnabled) { log(OWNER_HUNTER, VERB_DECODED, data.logId()); } stats.dispatchBitmapDecoded(bitmap); 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; }
上述注释1就是从内存中获取图片,如果取不到图片注释2由RequestHandler.load拿到图片数据的流的结果对象,然后解析成图片,注释3在拿到图片之后,对图片根据控件的大小进行转换。拿到图片之后,发送消息code为HUNTER_COMPLETE的消息到MessageQueue中,
if (result == null) { dispatcher.dispatchFailed(this); } else { dispatcher.dispatchComplete(this); }
接着dispatcherHandler执行
case HUNTER_COMPLETE: { BitmapHunter hunter = (BitmapHunter) msg.obj; dispatcher.performComplete(hunter); break; }
void performComplete(BitmapHunter hunter) { if (shouldWriteToMemoryCache(hunter.getMemoryPolicy())) { cache.set(hunter.getKey(), hunter.getResult()); } hunterMap.remove(hunter.getKey()); batch(hunter);//1 if (hunter.getPicasso().loggingEnabled) { log(OWNER_DISPATCHER, VERB_BATCHED, getLogIdsForHunter(hunter), "for completion"); } }
进行内存中保存。完成图片的内存缓存之后,就是对图片设置到ImageView上,Dispatch的batch方法
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); }
其实上面的操作是将io线程切换到主线程上来,到绑定主线程Looper的handler接收到消息,会执行
case HUNTER_BATCH_COMPLETE: { @SuppressWarnings("unchecked") List<BitmapHunter> batch = (List<BitmapHunter>) msg.obj; //noinspection ForLoopReplaceableByForEach for (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);//1 } 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); } }
注释1就是将图片设置到Image的操作。
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()); } }
通过ImageViewAction执行界面的设置操作。
总结
上面其实只是一个源码的阅读流程记录而已,其实其中的更多的是设计思想的理解,设计模式的学习等,比如这里的Action接口,多个子类实现了该接口,都会执行compelete方法,这就是策略模式的模型,会根据你传入的是ImageViewAction还是GetAction来执行对应的complete,这样就需要判断是ImageViewAction还是GetAction来执行对应的操作;还有在初始化的时候,会在list中增加各种RequestHandler,然后在根据你传入的uri,找到对应的RequestHandler这种设计,个人觉得这种设计在解决一个问题有多种串行的尝试的时候,这个还是很有用。
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