Picasso流程解析
2019-03-19 本文已影响0人
陆元伟
Picasso流程解析
首先从调用代码看起
// Trigger the download of the URL asynchronously into the image view.
Picasso.with(context)
.load(url)
.placeholder(R.drawable.placeholder)
.error(R.drawable.error)
.resizeDimen(R.dimen.list_detail_image_size,R.dimen.list_detail_image_size)
.centerInside()
.into(holder.image);
很显然是单例模式
public static Picasso with(Context context) {
if (singleton == null) {
Class var1 = Picasso.class;
synchronized(Picasso.class) {
if (singleton == null) {
singleton = (new Picasso.Builder(context)).build();
}
}
}
return singleton;
}
再看load方法,对参数做了检查，调用了一个重载方法，返回的是一个RequestCreator对象
public RequestCreator load(@Nullable 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));
}
将String转换为Uri,直接生成一个RequestCreator对象，并把uri放入里面然后返回。后面的方法就在该对象里面调用了
public RequestCreator load(@Nullable Uri uri) {
return new RequestCreator(this,uri,0);
}
而这个uri。则放入到data里面，这个data是，Request的一个内部类Builder.
RequestCreator(Picasso picasso, Uri uri, int resourceId) {
if (picasso.shutdown) {
throw new IllegalStateException("Picasso instance already shut down. Cannot submit new requests.");
} else {
this.picasso = picasso;
this.data = new Builder(uri, resourceId, picasso.defaultBitmapConfig);
}
}
再往下看。placeholder方法就是设置还未下载图片之前占位资源id，这样先显示的就是这张图片
public RequestCreator placeholder(@DrawableRes int placeholderResId) {
//默认这个值为true,如果调用noPlaceholder方法则为false
if(!setPlaceholder) {
throw new IllegalStateException("Already explicitly declared as no placeholder.");
}
if(placeholderResId ==0) {
throw new IllegalArgumentException("Placeholder image resource invalid.");
}
//如果设置过placeholderDrawable,再调用这个方法就会抛异常。
if(placeholderDrawable!=null) {
throw new IllegalStateException("Placeholder image already set.");
}
this.placeholderResId= placeholderResId;
return this;
}
error方法设置如果发生错误是显示资源Id，和placeholder方法一样。
/** An error drawable to be used if the request image could not be loaded. */
public RequestCreator error(@DrawableRes int errorResId) {
if(errorResId ==0) {
throw new IllegalArgumentException("Error image resource invalid.");
}
if(errorDrawable!=null) {
throw new IllegalStateException("Error image already set.");
}
this.errorResId= errorResId;
return this;
}
接下来是resizeDimen方法,获取宽高。
public RequestCreator resizeDimen(int targetWidthResId, int targetHeightResId) {
Resources resources = this.picasso.context.getResources();
int targetWidth = resources.getDimensionPixelSize(targetWidthResId);
int targetHeight = resources.getDimensionPixelSize(targetHeightResId);
return this.resize(targetWidth, targetHeight);
}
然后把宽高放到data里面，这个data是Request的内部类Builder.
public RequestCreator resize(int targetWidth, int targetHeight) {
this.data.resize(targetWidth, targetHeight);
return this;
}
centerInside方法，也是调用data的方法。
public RequestCreator centerInside() {
this.data.centerInside();
return this;
}
最后看into方法。调用重载方法
public void into(ImageView target) {
this.into(target, (Callback)null);
}
这个方法代码比较长。
首先检查是否在主线程调用。如果不是则直接抛异常。因为后面要设置控件占位图片，或者从缓存中读取图片设置给控件，所有该方法一定要在主线程调用。
然后一系列参数判断。不过默认的值都会走到生成reqeust
利用request的信息生成key,因为缓存就是根据该key去获取的。
默认内存缓存是开启的。从内存缓存中获取，获取到了直接设置返回，啥事也就没有了。
没有缓存则判断是否设置了占位图片，如果设置了则先显示占位图片，根据生成一个Action.调用picasso的方法添加
public void into(ImageView target, Callback callback) {
long started = System.nanoTime();
//检查是否在主线程。不是则抛出异常。
Utils.checkMain();
if (target == null) {
throw new IllegalArgumentException("Target must not be null.");
//这里是查看data里面是否有uri.或者resourceId.因为前面构造RequestCreator的时候把uri传给了data.所以hasImage返回true
} else if (!this.data.hasImage()) {
this.picasso.cancelRequest(target);
if (this.setPlaceholder) {
PicassoDrawable.setPlaceholder(target, this.getPlaceholderDrawable());
}
} else {
//默认这个值是false.
if (this.deferred) {
if (this.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 (this.setPlaceholder) {
PicassoDrawable.setPlaceholder(target, this.getPlaceholderDrawable());
}
this.picasso.defer(target, new DeferredRequestCreator(this, target, callback));
return;
}
this.data.resize(width, height);
}
//利用data创造一个Request.因为之前设置的属性都设置到data里面。所以这里创建的时候传到了Request里面
Request request = this.createRequest(started);
//利用request的一些信息生成key.
String requestKey = Utils.createKey(request);
//如果设置了NO_CACHE，则不从内存缓存中获取。否则先从内存缓存中获取。默认缓存是LruCache
if (MemoryPolicy.shouldReadFromMemoryCache(this.memoryPolicy)) {
Bitmap bitmap = this.picasso.quickMemoryCacheCheck(requestKey);
//如果缓存中有。则取消请求。设置到目标控件上
if (bitmap != null) {
this.picasso.cancelRequest(target);
PicassoDrawable.setBitmap(target, this.picasso.context, bitmap, LoadedFrom.MEMORY, this.noFade, this.picasso.indicatorsEnabled);
if (this.picasso.loggingEnabled) {
Utils.log("Main", "completed", request.plainId(), "from " + LoadedFrom.MEMORY);
}
if (callback != null) {
callback.onSuccess();
}
return;
}
}
//如果设置了占位图片，先设置占位图片
if (this.setPlaceholder) {
PicassoDrawable.setPlaceholder(target, this.getPlaceholderDrawable());
}
//生成一个Action
Action action = new ImageViewAction(this.picasso, target, request, this.memoryPolicy, this.networkPolicy, this.errorResId, this.errorDrawable, requestKey, this.tag, callback, this.noFade);
//添加到队列并且提交
this.picasso.enqueueAndSubmit(action);
}
}
小结:with方法是创建一个Picasso单例出来，load方法是创建一个RequestCreator对象出来。后面的所有链式调用就都是在RequestCreator对象里面。RequestCreator对象主要是接收参数，并且校验参数。并且从内存缓存里面，如果存在则不用去网络请求，也就没Request和Action的什么事了。如果不存在，把一些必要的参数放到Action对象，然后提交出去。
下面再看看怎么处理网络请求的，接着上面从Picasso的enqueueAndSubmit看起
void enqueueAndSubmit(Action action) {
Object target = action.getTarget();
//如果已经有了该action.则取消。再重新放入
if (target != null && this.targetToAction.get(target) != action) {
this.cancelExistingRequest(target);
this.targetToAction.put(target, action);
}
this.submit(action);
}
void submit(Action action) {
this.dispatcher.dispatchSubmit(action);
}
调用Dispatcher对象的dispatchSubmit方法,发送一个what为1的message,该handler是一个内部类，并且不是获取主线程的loop。而是获取内部类DispatcherThread的loop。该类继承HandlerThread。也就是说handler是在子线程中处理Message的。
void dispatchSubmit(Action action) {
this.handler.sendMessage(this.handler.obtainMessage(1, action));
}
看handlerMessage方法里面处理消息为1的地方,调用了performSubmit方法。此时已经切换到子线程中运行了
public void handleMessage(final Message msg) {
Object tag;
BitmapHunter hunter;
Action action;
switch(msg.what) {
case 1:
action = (Action)msg.obj;
this.dispatcher.performSubmit(action);
break;
case 2:
调用重载方法
void performSubmit(Action action) {
this.performSubmit(action, true);
}
注释1.判断当前action的是否暂停了。如果暂停了。就不去请求。这个在配合列表使用更好。因为当滑动列表时，会产生很多请求，这个时候如果滑动的时候调用pauseTag方法，则就不会请求服务器。滑动完成后调用resumeTag，又会去请求服务器
注释2 判断是否有相同的action。这样就不用重复添加。
注释3则利用action，和其他信息生成一个BitmapHunter对象。该对象继承了Runnable对象。并且把该对象放入线程池中。既然是Runnable对象。那就看run方法
void performSubmit(Action action, boolean dismissFailed) {
//1判断集合Set中是否存在，由于没设置过，因此走else.如果设置了。则就不会请求。如果在列表中滑动会生成很多action。这样不可见的ImageView就可以设置pausedTag。
if (this.pausedTags.contains(action.getTag())) {
this.pausedActions.put(action.getTarget(), action);
if (action.getPicasso().loggingEnabled) {
Utils.log("Dispatcher", "paused", action.request.logId(), "because tag '" + action.getTag() + "' is paused");
}
} else {
//2 由于没设置过，故为null
BitmapHunter hunter = (BitmapHunter)this.hunterMap.get(action.getKey());
if (hunter != null) {
hunter.attach(action);
//线程池是否关闭了
} else if (this.service.isShutdown()) {
if (action.getPicasso().loggingEnabled) {
Utils.log("Dispatcher", "ignored", action.request.logId(), "because shut down");
}
} else {
//3生成了一个BitmapHunter对象，该对象继承了Runnable
hunter = BitmapHunter.forRequest(action.getPicasso(), this, this.cache, this.stats, action);
//提交到线程池
hunter.future = this.service.submit(hunter);
//把action的key 和hunter绑定在集合
this.hunterMap.put(action.getKey(), hunter);
if (dismissFailed) {
this.failedActions.remove(action.getTarget());
}
if (action.getPicasso().loggingEnabled) {
Utils.log("Dispatcher", "enqueued", action.request.logId());
}
}
}
}
BitmapHunter对象的run方法，设置线程名。然后调用hunt方法去获取。然后返回相应的回调。如果出现了异常，根据不同异常执行重试或者回调失败
public void run() {
try {
//设置线程名
updateThreadName(this.data);
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "executing", Utils.getLogIdsForHunter(this));
}
this.result = this.hunt();
if (this.result == null) {
this.dispatcher.dispatchFailed(this);
} else {
this.dispatcher.dispatchComplete(this);
}
} catch (ResponseException var10) {
if (!var10.localCacheOnly || var10.responseCode != 504) {
this.exception = var10;
}
this.dispatcher.dispatchFailed(this);
} catch (ContentLengthException var11) {
this.exception = var11;
//重新提交请求。
this.dispatcher.dispatchRetry(this);
} catch (IOException var12) {
this.exception = var12;
//重新提交请求。
this.dispatcher.dispatchRetry(this);
} catch (OutOfMemoryError var13) {
StringWriter writer = new StringWriter();
this.stats.createSnapshot().dump(new PrintWriter(writer));
this.exception = new RuntimeException(writer.toString(), var13);
this.dispatcher.dispatchFailed(this);
} catch (Exception var14) {
this.exception = var14;
this.dispatcher.dispatchFailed(this);
} finally {
Thread.currentThread().setName("Picasso-Idle");
}
}
hunt方法。这个方法比较长。看主要部分的，这里也先是取缓存中获取。如果存在，则直接返回。如果不存在，则调用requestHandler去处理。
Bitmap hunt() throws IOException {
Bitmap bitmap = null;
//1 如果可以从缓存中获取。去缓存获取。
if (MemoryPolicy.shouldReadFromMemoryCache(this.memoryPolicy)) {
bitmap = this.cache.get(this.key);
if (bitmap != null) {
this.stats.dispatchCacheHit();
this.loadedFrom = LoadedFrom.MEMORY;
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "decoded", this.data.logId(), "from cache");
}
return bitmap;
}
}
this.data.networkPolicy = this.retryCount == 0 ? NetworkPolicy.OFFLINE.index : this.networkPolicy;
//2 通过requestHandler去获取
Result result = this.requestHandler.load(this.data, this.networkPolicy);
...
}
return bitmap;
}
requestHandler是创建BitmapHunter的时候传进来的。这里获取Picasso里面RequestHandler的集合。而requestHandlers里面有什么呢？
static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats, Action action) {
Request request = action.getRequest();
List<RequestHandler> requestHandlers = picasso.getRequestHandlers();
int i = 0;
for(int count = requestHandlers.size(); i < count; ++i) {
RequestHandler 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);
}
创建Picasso的时候就已经放置很多RequestHandler在里面,根据load方法传进来的字符串资源分别对应不一样的处理对象。这样我们就可以在load方法里面传入资源文件或者文件路径或者网络url等等
List<RequestHandler> 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));
this.requestHandlers = Collections.unmodifiableList(allRequestHandlers);
由于我们传进来的是url。所以这里的requestHandler就是NetworkRequestHandler处理
看NetworkRequestHandler方法处理,这个downloader也是Picasso类里面创建的。并且里面用的是OkHttp
public Result load(Request request, int networkPolicy) throws IOException {
Response response = this.downloader.load(request.uri, request.networkPolicy);
if (response == null) {
return null;
} else {
LoadedFrom loadedFrom = response.cached ? LoadedFrom.DISK : LoadedFrom.NETWORK;
Bitmap bitmap = response.getBitmap();
//返回bitmap
if (bitmap != null) {
return new Result(bitmap, loadedFrom);
} else {
InputStream is = response.getInputStream();
if (is == null) {
return null;
} else if (loadedFrom == LoadedFrom.DISK && response.getContentLength() == 0L) {
Utils.closeQuietly(is);
throw new NetworkRequestHandler.ContentLengthException("Received response with 0 content-length header.");
} else {
if (loadedFrom == LoadedFrom.NETWORK && response.getContentLength() > 0L) {
this.stats.dispatchDownloadFinished(response.getContentLength());
}
return new Result(is, loadedFrom);
}
}
}
}
继续看hunt方法
Bitmap hunt() throws IOException {
Bitmap bitmap = null;
...
Result result = this.requestHandler.load(this.data, this.networkPolicy);
if (result != null) {
this.loadedFrom = result.getLoadedFrom();
this.exifRotation = result.getExifOrientation();
bitmap = result.getBitmap();
if (bitmap == null) {
InputStream is = result.getStream();
try {
bitmap = decodeStream(is, this.data);
} finally {
Utils.closeQuietly(is);
}
}
}
if (bitmap != null) {
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "decoded", this.data.logId());
}
this.stats.dispatchBitmapDecoded(bitmap);
//如果需要缩放或者旋转处理。
if (this.data.needsTransformation() || this.exifRotation != 0) {
Object var10 = DECODE_LOCK;
synchronized(DECODE_LOCK) {
if (this.data.needsMatrixTransform() || this.exifRotation != 0) {
bitmap = transformResult(this.data, bitmap, this.exifRotation);
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "transformed", this.data.logId());
}
}
if (this.data.hasCustomTransformations()) {
bitmap = applyCustomTransformations(this.data.transformations, bitmap);
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "transformed", this.data.logId(), "from custom transformations");
}
}
}
if (bitmap != null) {
this.stats.dispatchBitmapTransformed(bitmap);
}
}
}
return bitmap;
}
继续往前看hunt调用的地方，如果已经获取到bitmap了，调用dispatcher的dispatchComplete方法
public void run() {
try {
//设置线程名
updateThreadName(this.data);
if (this.picasso.loggingEnabled) {
Utils.log("Hunter", "executing", Utils.getLogIdsForHunter(this));
}
this.result = this.hunt();
if (this.result == null) {
this.dispatcher.dispatchFailed(this);
} else {
this.dispatcher.dispatchComplete(this);
}
}
...
}
Dispatcher的dispatchComplete方法
void dispatchComplete(BitmapHunter hunter) {
this.handler.sendMessage(this.handler.obtainMessage(4, hunter));
}
case 4:````````
hunter = (BitmapHunter)msg.obj;
this.dispatcher.performComplete(hunter);
break;
调用performComplete方法，设置了缓存
void performComplete(BitmapHunter hunter) {
if (MemoryPolicy.shouldWriteToMemoryCache(hunter.getMemoryPolicy())) {
this.cache.set(hunter.getKey(), hunter.getResult());
}
this.hunterMap.remove(hunter.getKey());
this.batch(hunter);
if (hunter.getPicasso().loggingEnabled) {
Utils.log("Dispatcher", "batched", Utils.getLogIdsForHunter(hunter), "for completion");
}
}
又发了一个消息
private void batch(BitmapHunter hunter) {
if (!hunter.isCancelled()) {
this.batch.add(hunter);
if (!this.handler.hasMessages(7)) {
this.handler.sendEmptyMessageDelayed(7, 200L);
}
}
}
处理消息。调用了performBatchComplete
public void handleMessage(final Message msg) {
Object tag;
BitmapHunter hunter;
Action action;
switch(msg.what) {
...
case 7:
this.dispatcher.performBatchComplete();
break;
发到主线程中去了，这主线程是Pacasso里面的
void performBatchComplete() {
List<BitmapHunter> copy = new ArrayList(this.batch);
this.batch.clear();
this.mainThreadHandler.sendMessage(this.mainThreadHandler.obtainMessage(8, copy));
this.logBatch(copy);
}
Picasso里面的handleMessage方法
public void handleMessage(Message msg) {
...
case 8:
batch = (List)msg.obj;
i = 0;
for(n = batch.size(); i < n; ++i) {
BitmapHunter hunter = (BitmapHunter)batch.get(i);
hunter.picasso.complete(hunter);
}
return;
调用了complete方法，我们这里的single是个ImageViewAction.后deliverAction会调用ImageViewAction里面的complete方法
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) {
Uri uri = hunter.getData().uri;
Exception exception = hunter.getException();
Bitmap result = hunter.getResult();
Picasso.LoadedFrom from = hunter.getLoadedFrom();
if (single != null) {
this.deliverAction(result, from, single);
}
if (hasMultiple) {
int i = 0;
for(int n = joined.size(); i < n; ++i) {
Action join = (Action)joined.get(i);
this.deliverAction(result, from, join);
}
}
if (this.listener != null && exception != null) {
this.listener.onImageLoadFailed(this, uri, exception);
}
}
}
ImageViewAction的complete方法。
public void complete(Bitmap result, LoadedFrom from) {
if (result == null) {
throw new AssertionError(String.format("Attempted to complete action with no result!\n%s", this));
} else {
ImageView target = (ImageView)this.target.get();
if (target != null) {
Context context = this.picasso.context;
boolean indicatorsEnabled = this.picasso.indicatorsEnabled;
PicassoDrawable.setBitmap(target, context, result, from, this.noFade, indicatorsEnabled);
if (this.callback != null) {
this.callback.onSuccess();
}
}
}
}
}
至此完成
小结:Dispatcher里面有个DispatcherThread线程，该线程继承HandlerThread类，里面的DispatcherHandler类用的就是DispatcherThread的loop.这样就可以方便的把代码切换到子线程。主要的工作是在BitmapHunter类的run方法。并且里面的下载用的是Okhttp。下载完成后如果设置了大小的，或者自定义处理的。都在获取后操作bitmap的。
