目录
Picasso加载一张图片的流程
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创建
//通过定义一个PicassoProvider来获取Context //单例创建Picasso实例 public static Picasso get() { if (singleton == null) { synchronized (Picasso.class) { if (singleton == null) { if (PicassoProvider.context == null) { throw new IllegalStateException("context == null"); } singleton = new Builder(PicassoProvider.context).build(); } } } return singleton; } //在AndroidManifest.xml中声明 @RestrictTo(LIBRARY) public final class PicassoProvider extends ContentProvider { @SuppressLint("StaticFieldLeak") static Context context; @Override public boolean onCreate() { context = getContext(); return true; } }
aaaa.png
build( ) 创建Picasso实例
/** Create the {@link Picasso} instance. */
public Picasso build() {
Context context = this.context;
//创建默认下载器
if (downloader == null) {
downloader = new OkHttp3Downloader(context);
}
//创建LRU内存缓存
if (cache == null) {
cache = new LruCache(context);
}
//创建线程池，默认有3个执行线程
if (service == null) {
service = new PicassoExecutorService();
}
//创建默认transformer
if (transformer == null) {
transformer = RequestTransformer.IDENTITY;
}
//统计
Stats stats = new Stats(cache);
//调度
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
}
//Picasso构造方法 对象赋值&创建一个新对象
//最主要的是初始化了allRequestHandlers 除了自定义的extraRequestHandlers 添加了7个默认的RequestHandler
Picasso(Context context, Dispatcher dispatcher, Cache cache, Listener listener,
RequestTransformer requestTransformer, List 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 allRequestHandlers = new ArrayList<>(builtInHandlers + extraCount);
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);
//省略...
}
public abstract class RequestHandler {
//来判断当前类型的RequestHandler能否处理request
public abstract boolean canHandleRequest(Request data);
//使用传入的requst来加载图片，加载的结果放入Result中返回
@Nullable
public abstract Result load(Request request, int networkPolicy) throws IOException;
//待定
int getRetryCount() {
return 0;
}
//待定
boolean shouldRetry(boolean airplaneMode, NetworkInfo info) {
return false;
}
//待定
boolean supportsReplay() {
return false;
}
}
创建好Picasso实例后，便是load了
//load的几个重载方法最后都会来调用参数为Uri的方法 生成一个RequestCreator，
//来执行接下来的trannform() rotate() into()等操作
public RequestCreator load(@Nullable Uri uri) {
return new RequestCreator(this, uri, 0);
}
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入队
//通过构造方法传入一个Picasso实例的引用，并且创建一个Request.Builder()的实例 //为创建一个Request做准备 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); }将我们需要加载的图片的信息都保存在data里面，我们设置centerCrop( )或者transform( )实际上都是对data内对应的变量标识进行设置，然后在into( )中进行build 生成一个Request，
然后看一下into( )方法的实现
public void into(ImageView target, Callback callback) { long started = System.nanoTime(); //检查是否在主线程 checkMain(); if (target == null) { throw new IllegalArgumentException("Target must not be null."); } //如果没有设置要加载的图片的Uri或者resourceId，直接设置占位图然后返回 if (!data.hasImage()) { picasso.cancelRequest(target); if (setPlaceholder) { setPlaceholder(target, getPlaceholderDrawable()); } return; } //是否延时加载，也就是选择fit()模式 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()); } //监听ImageView的ViewTreeObserver.OnPreDrawListener接口,一旦ImageView //的宽高被赋值,就按照ImageView的宽高继续加载. picasso.defer(target, new DeferredRequestCreator(this, target, callback)); return; } data.resize(width, height); } //构建request Request request = createRequest(started); String requestKey = createKey(request); //是否要从内存中读取 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; } } //缓存中没有，先设置占位图，然后构建一个ImageViewAction if (setPlaceholder) { setPlaceholder(target, getPlaceholderDrawable()); } //Action的实现类保存了这次加载需要的所有信息，还提供了加载完成后的回调方法 Action action = new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId, errorDrawable, requestKey, tag, callback, noFade); //将Action对象提交到队列 picasso.enqueueAndSubmit(action); }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); } //提交Action 最后转到Dispatcher类的 dispatchSubmit方法 submit(action); } void submit(Action action) { dispatcher.dispatchSubmit(action); } //Dispatcher类的dispatchXXX系列方法都是通过一个Handler来发送消息看一下Dispatcher的主要实现
Dispatcher(Context context, ExecutorService service, Handler mainThreadHandler, Downloader downloader, Cache cache, Stats stats) { this.dispatcherThread = new DispatcherThread(); this.dispatcherThread.start(); this.handler = new DispatcherHandler(dispatcherThread.getLooper(), this); this.mainThreadHandler = mainThreadHandler; } void dispatchSubmit(Action action) { handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action)); } static class DispatcherThread extends HandlerThread { DispatcherThread() { super(Utils.THREAD_PREFIX + DISPATCHER_THREAD_NAME, THREAD_PRIORITY_BACKGROUND); } } private static class DispatcherHandler extends Handler { private final Dispatcher dispatcher; DispatcherHandler(Looper looper, Dispatcher dispatcher) { super(looper); this.dispatcher = dispatcher; } @Override public void handleMessage(final Message msg) { switch (msg.what) { case REQUEST_SUBMIT: { Action action = (Action) msg.obj; dispatcher.performSubmit(action); break; //省略... } } }首先自己创建了一个DispatcherThread子线程，然后创建了DispatcherHandler对象，用这个Handler来进行发送消息，而在DispatcherHandler的handleMessage中，最终调用了dispatcher.performXXX(action);等方法
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执行、解码、变化
来看一下performSubmit( )方法的实现
void performSubmit(Action action, boolean dismissFailed) { //如果pausedActions包含这个Action，则暂停 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; } //此Action对应的hunter存在，attach后直接返回 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; } //构建hunter对象 实现了Runnable接口 hunter = forRequest(action.getPicasso(), this, cache, stats, action); //通过ExecutorService执行hunter，并返回future对象。 //提交线程池执行 hunter.future = service.submit(hunter); //将构造好的hunter对象加入到hunterMap缓存起来 hunterMap.put(action.getKey(), hunter); if (dismissFailed) { failedActions.remove(action.getTarget()); } if (action.getPicasso().loggingEnabled) { log(OWNER_DISPATCHER, VERB_ENQUEUED, action.request.logId()); } }static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats, Action action) { Request request = action.getRequest(); ListrequestHandlers = picasso.getRequestHandlers(); //通过遍历所有的requestHandlers（包括自定的和默认添加的那7个）寻找能处理这个Request的requestHandler //使用这个requestHandler来构建BitmapHunter for (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实现了Runable接口，并且通过ExecutorService来执行，接下来就看一下BitmapHunter的run( )方法 @Override public void run() { try { updateThreadName(data); if (picasso.loggingEnabled) { log(OWNER_HUNTER, VERB_EXECUTING, getLogIdsForHunter(this)); } //调用hunt()方法并且返回一个Bitmap对象 result = hunt(); //然后根绝结果调用Dispatcher的dispatchXXX系列方法来发送不同的消息 if (result == null) { dispatcher.dispatchFailed(this); } else { dispatcher.dispatchComplete(this); } } catch (NetworkRequestHandler.ResponseException e) { if (!NetworkPolicy.isOfflineOnly(e.networkPolicy) || e.code != 504) { exception = e; } dispatcher.dispatchFailed(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); } } /** * Global lock for bitmap decoding to ensure that we are only decoding one at a time. Since * this will only ever happen in background threads we help avoid excessive memory thrashing as * well as potential OOMs. Shamelessly stolen from Volley. */ private static final Object DECODE_LOCK = new Object(); //hunter方法 Bitmap hunt() throws IOException { Bitmap bitmap = null; //是否可以从缓存中读取 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; } } networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy; //调用requestHandler的load方法得到一个result //load方法在不同的requestHandler中有不同的实现 //(解码) 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) { Source source = result.getSource(); try { bitmap = decodeStream(source, data); } finally { try { //noinspection ConstantConditions If bitmap is null then source is guranteed non-null. source.close(); } catch (IOException ignored) { } } } } if (bitmap != null) { if (picasso.loggingEnabled) { log(OWNER_HUNTER, VERB_DECODED, data.logId()); } stats.dispatchBitmapDecoded(bitmap); //处理Transformation（变化） if (data.needsTransformation() || exifOrientation != 0) { //图片在转化的时候需要一片临时内存，加全局锁解决瞬时OOOM的问题 //或者使用synchronized(BitmapHunter.class){} 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); } } } //返回Bitmap return bitmap; } 最后拿到result之后，会调用dispatcher.dispatchComplete(this)，最终会调用dispatcher.performComplete()方法
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批处理
void performComplete(BitmapHunter hunter) { //是否加入缓存 if (shouldWriteToMemoryCache(hunter.getMemoryPolicy())) { cache.set(hunter.getKey(), hunter.getResult()); } //完成后hunterMap中移除 hunterMap.remove(hunter.getKey()); batch(hunter); if (hunter.getPicasso().loggingEnabled) { log(OWNER_DISPATCHER, VERB_BATCHED, getLogIdsForHunter(hunter), "for completion"); } } //批处理 private void batch(BitmapHunter hunter) { if (hunter.isCancelled()) { return; } if (hunter.result != null) { hunter.result.prepareToDraw(); } batch.add(hunter); if (!handler.hasMessages(HUNTER_DELAY_NEXT_BATCH)) { //Handler中调用performBatchComplete handler.sendEmptyMessageDelayed(HUNTER_DELAY_NEXT_BATCH, BATCH_DELAY); } } void performBatchComplete() { Listcopy = new ArrayList<>(batch); batch.clear(); //消息发动到主线程进行处理 mainThreadHandler.sendMessage(mainThreadHandler.obtainMessage(HUNTER_BATCH_COMPLETE, copy)); logBatch(copy); } //mainThreadHandler中 //... case HUNTER_BATCH_COMPLETE: { @SuppressWarnings("unchecked") List batch = (List ) msg.obj; //noinspection ForLoopReplaceableByForEach for (int i = 0, n = batch.size(); i < n; i++) { BitmapHunter hunter = batch.get(i); //调用Picasso#complete方法 hunter.picasso.complete(hunter); } break; } //... -
完成、分发
接着看一下Picasso#complete( )方法的实现
void complete(BitmapHunter hunter) { //获取执行的那个Action Action single = hunter.getAction(); //获取被添加进来的Action Listjoined = 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(); //分发 if (single != null) { deliverAction(result, from, single, exception); } if (hasMultiple) { //noinspection ForLoopReplaceableByForEach for (int i = 0, n = joined.size(); i < n; i++) { Action join = joined.get(i); deliverAction(result, from, join, exception); } } if (listener != null && exception != null) { listener.onImageLoadFailed(this, uri, exception); } } //deliverAction的实现 //此方法的主要实现就是回调Action的complete方法或者error方法 private void deliverAction(Bitmap result, LoadedFrom from, Action action, Exception e) { 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(e); if (loggingEnabled) { log(OWNER_MAIN, VERB_ERRORED, action.request.logId(), e.getMessage()); } } } -
显示
之前分析是看到，这个加载流程这里的Action是ImageViewAction，下面看一下ImageViewAction对应的实现
@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)); } //获取要显示的ImageView ImageView target = this.target.get(); if (target == null) { return; } Context context = picasso.context; boolean indicatorsEnabled = picasso.indicatorsEnabled; //通过PicassoDrawable来将bitmap设置到ImageView上 PicassoDrawable.setBitmap(target, context, result, from, noFade, indicatorsEnabled); if (callback != null) { callback.onSuccess(); } } //使用PicassoDrawable来设置Bitmap，主要是为了设置渐变的加载动画 -
PicassoDrawable渐变动画
PicassoDrawable(Context context, Bitmap bitmap, Drawable placeholder, Picasso.LoadedFrom loadedFrom, boolean noFade, boolean debugging) { super(context.getResources(), bitmap); this.debugging = debugging; this.density = context.getResources().getDisplayMetrics().density; this.loadedFrom = loadedFrom; //noFade为false，并且不是从内存中加载的时候，才会有渐变动画 boolean fade = loadedFrom != MEMORY && !noFade; if (fade) { this.placeholder = placeholder; animating = true; startTimeMillis = SystemClock.uptimeMillis(); } } @Override public void draw(Canvas canvas) { if (!animating) { super.draw(canvas); } else { float normalized = (SystemClock.uptimeMillis() - startTimeMillis) / FADE_DURATION; if (normalized >= 1f) { animating = false; placeholder = null; super.draw(canvas); } else { if (placeholder != null) { placeholder.draw(canvas); } //渐变动画 // setAlpha will call invalidateSelf and drive the animation. int partialAlpha = (int) (alpha * normalized); super.setAlpha(partialAlpha); super.draw(canvas); super.setAlpha(alpha); } } if (debugging) { drawDebugIndicator(canvas); } }