基本用法
从最基本的用法开始
Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);
1，with
让我们先从with方法开始
public static Picasso with(Context context) {
if (singleton == null) {
synchronized (Picasso.class) {
if (singleton == null) {
singleton = new Builder(context).build();
}
}
}
return singleton;
}
static volatile Picasso singleton = null;
一个标准懒汉式Double Check单例模式，
/** Start building a new {@link Picasso} instance. */
public Builder(Context context) {
if (context == null) {
throw new IllegalArgumentException("Context must not be null.");
}
this.context = context.getApplicationContext();
}
/** Create the {@link Picasso} instance. */
public Picasso build() {
Context context = this.context;
//下载器
if (downloader == null) {
downloader = Utils.createDefaultDownloader(context);
}
//LRU缓存
if (cache == null) {
cache = new LruCache(context);
}
//线程池
if (service == null) {
service = new PicassoExecutorService();
}
if (transformer == null) {
transformer = RequestTransformer.IDENTITY;
}
Stats stats = new Stats(cache);
//事件分发者
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
}
}
内部使用构建者模式，将downloader（下载图片用），lru缓存（内存缓存），线程池（执行下载解析图片的Runnable），dispatcher（picasso内部事件调度者）初始化
最后我们可以获取一个单例的Picasso实例
让我们接下来看load方法
2，load方法
在picasso类中有4个重载，我们先看String类型的
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));
}
如果path为空，直接回返回一个RequestCreator，如果不为空，会调用Uri的重载
让我们看看File对象的重载
public RequestCreator load(File file) {
if (file == null) {
return new RequestCreator(this, null, 0);
}
return load(Uri.fromFile(file));
}
同样，最后也是调用Uri的重载，
/**
* Start an image request using the specified URI.
*
* Passing {@code null} as a {@code uri} will not trigger any request but will set a placeholder,
* if one is specified.
*
* @see #load(File)
* @see #load(String)
* @see #load(int)
*/
public RequestCreator load(Uri uri) {
return new RequestCreator(this, uri, 0);
}
int类型的重载和上面不一样，入参是资源ID
public RequestCreator load(int resourceId) {
if (resourceId == 0) {
throw new IllegalArgumentException("Resource ID must not be zero.");
}
return new RequestCreator(this, null, resourceId);
}
好了，以上几个方法，每次调用都会生成一个RequestCreator对象，让我们看看他的构造方法
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);
}
里面用构建者模式，开始准备一个request，但是还没有发送
Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);
从load方法后，我们实际调用的是RequestCreator对象，我们可以根据需求，调用RequestCreator方法
往Request里修改东西，比如centerCrop等等
3，into
接下来看into方法，into方法有5个重载
我们先从ImageView的重载开始看
public void into(ImageView target) {
into(target, null);
}
调用两个方法的重载
/**
* Asynchronously fulfills the request into the specified {@link ImageView} and invokes the
* target {@link Callback} if it's not {@code null}.
*
* Note: The {@link Callback} param is a strong reference and will prevent your
* {@link android.app.Activity} or {@link android.app.Fragment} from being garbage collected. If
* you use this method, it is strongly recommended you invoke an adjacent
* {@link Picasso#cancelRequest(android.widget.ImageView)} call to prevent temporary leaking.
*/
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);
}
方法比较长，我们一点点来看
checkMain();
static void checkMain() {
if (!isMain()) {
throw new IllegalStateException("Method call should happen from the main thread.");
}
}
static boolean isMain() {
return Looper.getMainLooper().getThread() == Thread.currentThread();
}
检测线程，如果调用into方法的线程不是主线程会报异常
"Method call should happen from the main thread."
再往下看
if (!data.hasImage()) {
picasso.cancelRequest(target);
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
return;
}
boolean hasImage() {
return uri != null || resourceId != 0;
}
调用request对象hasImage，如果uri和resourceId都没有，就会取消交易，如果有图片占位符，则会直接显示占位符
接下来看
if (deferred) {
//fit不能和resize一起使用
if (data.hasSize()) {
throw new IllegalStateException("Fit cannot be used with resize.");
}
//获取ImageView宽高
int width = target.getWidth();
int height = target.getHeight();
//如果宽和高中有一个是0
if (width == 0 || height == 0) {
//如果设置过图片占位符，则会先显示占位符
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
//调用defer方法，延迟调用任务，返
picasso.defer(target, new DeferredRequestCreator(this, target, callback));
return;
}
//如果target这个ImageView宽高都不为0，则，图片之后会被调整大小和ImageView一样大
data.resize(width, height);
}
deferred是一个RequestCreator类的成员变量，是否延期的意思，如果之前调用过RequestCreator的fit方法，会把deferred值为true
/**
* Attempt to resize the image to fit exactly into the target {@link ImageView}'s bounds. This
* will result in delayed execution of the request until the {@link ImageView} has been laid out.
*
* Note: This method works only when your target is an {@link ImageView}.
*/
public RequestCreator fit() {
deferred = true;
return this;
}
让我们继续into方法继续往下看
Request request = createRequest(started);
/** Create the request optionally passing it through the request transformer. */
private Request createRequest(long started) {
int id = nextId.getAndIncrement();
//这里通过build把request对象，构建好了
Request request = data.build();
request.id = id;
request.started = started;
boolean loggingEnabled = picasso.loggingEnabled;
if (loggingEnabled) {
log(OWNER_MAIN, VERB_CREATED, request.plainId(), request.toString());
}
//如果之前有设置过requestTransformer，会对request进行transform
Request transformed = picasso.transformRequest(request);
if (transformed != request) {
// If the request was changed, copy over the id and timestamp from the original.
transformed.id = id;
transformed.started = started;
if (loggingEnabled) {
log(OWNER_MAIN, VERB_CHANGED, transformed.logId(), "into " + transformed);
}
}
return transformed;
}
我们继续从into往下看
String requestKey = createKey(request);
这个方法，主要是之后图片内存缓存标志
接下来看
//判断是否从内存获取图片
if (shouldReadFromMemoryCache(memoryPolicy)) {
//根据之前生成的key，从内存中获取缓存的bitmap
Bitmap bitmap = picasso.quickMemoryCacheCheck(requestKey);
//如果内存中有，则会完成请求
if (bitmap != null) {
picasso.cancelRequest(target);
//将图片设置给ImageView
setBitmap(target, picasso.context, bitmap, MEMORY, noFade, picasso.indicatorsEnabled);
if (picasso.loggingEnabled) {
log(OWNER_MAIN, VERB_COMPLETED, request.plainId(), "from " + MEMORY);
}
//如果设置了回调，则会调用onSuccess
if (callback != null) {
callback.onSuccess();
}
return;
}
}
我们继续into方法往下看
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
设置占位符
Action action =
new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId,
errorDrawable, requestKey, tag, callback, noFade);
picasso.enqueueAndSubmit(action);
到这里，我们要开始异步请求图片了
void enqueueAndSubmit(Action action) {
Object target = action.getTarget();
if (target != null && targetToAction.get(target) != action) {
//如果现在map中有一个ImageView正在进行的请求，或者还没有请求
// This will also check we are on the main thread.
// 取消当前的请求
cancelExistingRequest(target);
targetToAction.put(target, action);//将target为key，action为值，塞进map中
}
submit(action);
}
让我们来看看submit方法
void submit(Action action) {
dispatcher.dispatchSubmit(action);
}
调用Dispatcher来之前创建的Action
dispatcher在picasso.builder build方法中创建
void dispatchSubmit(Action action) {
handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action));
}
内部通过handler来传递消息
这个handler再Dispatcher构造方法中初始化，传入的DispatcherThread的looper，DispatcherThread继承自HandlerThread，当这个线程运行的时候，会自动创建一个looper
实际上走的是DispatcherHandler，让我们看看这个类
找到handlerMessage中REQUEST_SUBMIT这个分支，调用了dispatcher的performSubmit的方法
void performSubmit(Action action) {
performSubmit(action, true);
}
void performSubmit(Action action, boolean dismissFailed) {
//如果当前action处于pause状态，会暂停加载，并且放入pausedActions中缓存起来
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;
}
//这里我们先忽略这一段
BitmapHunter hunter = hunterMap.get(action.getKey());
if (hunter != null) {
hunter.attach(action);
return;
}
//如果线程池已经关闭了，则会直接返回
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());
}
}
先看看forRequest方法
static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats,
Action action) {
Request request = action.getRequest();
List requestHandlers = picasso.getRequestHandlers();
// Index-based loop to avoid allocating an iterator.
//noinspection ForLoopReplaceableByForEach
//遍历requestHandlers，看看是否有可以处理这个request的handler
for (int i = 0, count = requestHandlers.size(); i < count; i++) {
RequestHandler requestHandler = requestHandlers.get(i);
//如果找到了就返回
if (requestHandler.canHandleRequest(request)) {
return new BitmapHunter(picasso, dispatcher, cache, stats, action, requestHandler);
}
}
//没找到会把一个错误的默认handler传回去
return new BitmapHunter(picasso, dispatcher, cache, stats, action, ERRORING_HANDLER);
}
最后会返回一个BitmapHunter，他继承自Runnable
我们继续看之前Dispatcher类的performSubmit方法
hunter.future = service.submit(hunter);
会把刚刚生产的hunter交给线程池去执行，这个线程池也是在picasso构建的时候生成
我们继续看刚刚的BitmapHunter，既然是Runnable，我们先看看他的run方法
@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);
}
·····
}
调用hunt方法，result就是返回的bitmap，那么核心从硬盘网络读取bitmap就是hunt方法了
Bitmap hunt() throws IOException {
Bitmap bitmap = null;
//是否从内存中读取
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;
}
}
data.networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy;
//通过之前匹配的RequestHandler来处理这个request
RequestHandler.Result result = requestHandler.load(data, networkPolicy);
···
return bitmap;
}
我们回头看，在picasso构造的时候，已经加入了好多个RequestHandler
从这里我们可以看到picasso支持的几种获取图片的途径
依次是联系人相册，媒体库，ContentResolver，asset，文件，网络
我们随便挑一个看看
如果之前Picasso的load方法传入的是file对象，则会走FileRequestHandler
如果之前传入的string里是http路径，则会走NetworkRequestHandler
让我们来看看NetworkRequestHandler的实现
@Override public Result load(Request request, int networkPolicy) throws IOException {
//调用downloader的load方法， downloader有两个实现，一个是okhttp，一个是urlconnection
Response response = downloader.load(request.uri, request.networkPolicy);
//如果没有结果，则会返回
if (response == null) {
return null;
}
Picasso.LoadedFrom loadedFrom = response.cached ? DISK : NETWORK;
//获取图片
Bitmap bitmap = response.getBitmap();
if (bitmap != null) {
//如果获取到了图片，则会返回
return new Result(bitmap, loadedFrom);
}
InputStream is = response.getInputStream();
if (is == null) {
return null;
}
// Sometimes response content length is zero when requests are being replayed. Haven't found
// root cause to this but retrying the request seems safe to do so.
if (loadedFrom == DISK && response.getContentLength() == 0) {
Utils.closeQuietly(is);
throw new ContentLengthException("Received response with 0 content-length header.");
}
if (loadedFrom == NETWORK && response.getContentLength() > 0) {
stats.dispatchDownloadFinished(response.getContentLength());
}
return new Result(is, loadedFrom);
}
最新的方法里，downloader返回的response都不会直接返回bitmap，而是inputstream
最后load方法会把inputsteam流封装人result返回
回到BitmapHunter hunt方法
Bitmap hunt() throws IOException {
```
RequestHandler.Result result = requestHandler.load(data, networkPolicy);
if (result != null) {
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 {
//从inputstream转换成bitmap
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() || exifRotation != 0) {
synchronized (DECODE_LOCK) {
if (data.needsMatrixTransform() || exifRotation != 0) {
//如果图片中Exif有旋转信息，进行旋转
bitmap = transformResult(data, bitmap, exifRotation);
if (picasso.loggingEnabled) {
log(OWNER_HUNTER, VERB_TRANSFORMED, data.logId());
}
}
if (data.hasCustomTransformations()) {
//如果requestCreator设置了transformation
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;
}
我们先来看decodeStream方法
/**
* Decode a byte stream into a Bitmap. This method will take into account additional information
* about the supplied request in order to do the decoding efficiently (such as through leveraging
* {@code inSampleSize}).
*/
static Bitmap decodeStream(InputStream stream, Request request) throws IOException {
MarkableInputStream markStream = new MarkableInputStream(stream);
stream = markStream;
long mark = markStream.savePosition(65536); // TODO fix this crap.
final BitmapFactory.Options options = RequestHandler.createBitmapOptions(request);
final boolean calculateSize = RequestHandler.requiresInSampleSize(options);
boolean isWebPFile = Utils.isWebPFile(stream);
markStream.reset(mark);
// When decode WebP network stream, BitmapFactory throw JNI Exception and make app crash.
// Decode byte array instead
if (isWebPFile) {
byte[] bytes = Utils.toByteArray(stream);
if (calculateSize) {
BitmapFactory.decodeByteArray(bytes, 0, bytes.length, options);
RequestHandler.calculateInSampleSize(request.targetWidth, request.targetHeight, options,
request);
}
return BitmapFactory.decodeByteArray(bytes, 0, bytes.length, options);
} else {
if (calculateSize) {
BitmapFactory.decodeStream(stream, null, options);
RequestHandler.calculateInSampleSize(request.targetWidth, request.targetHeight, options,
request);
markStream.reset(mark);
}
Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);
if (bitmap == null) {
// Treat null as an IO exception, we will eventually retry.
throw new IOException("Failed to decode stream.");
}
return bitmap;
}
}
在这里获取request中的图片格式（config） 和 设置好的宽高（resize方法）
config如果之前没有设置，默认是ARGB_8888，
如果设置了resize，在这里则会使用inSampleSize调整图片大小，否则会按默认大小加载
然后回到run方法
返回给dispatcher
void dispatchComplete(BitmapHunter hunter) {
handler.sendMessage(handler.obtainMessage(HUNTER_COMPLETE, hunter));
}
回到DispatcherHandler
去到dispatcher的performComplete
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");
}
}
在这里，根据对request设置的内存策略，判断需不需要内存缓存，
如果需要，会放入LRUCache里
重点看batch，准备批量任务
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);
}
}
回到DispatcerHandler
void performBatchComplete() {
List copy = new ArrayList(batch);
batch.clear();
mainThreadHandler.sendMessage(mainThreadHandler.obtainMessage(HUNTER_BATCH_COMPLETE, copy));
logBatch(copy);
}
批量任务都已经准备就绪
static final Handler HANDLER = new Handler(Looper.getMainLooper()) {
@Override public void handleMessage(Message msg) {
switch (msg.what) {
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);
//
hunter.picasso.complete(hunter);
}
break;
}
···
}
}
};
最后for循环遍历batch
hunter.picasso.complete(hunter);
调用picasso的complete
void complete(BitmapHunter hunter) {
Action single = hunter.getAction();
List 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);
}
}
终于看到了complete方法，但是还没完，这里核心是走deliverAction方法
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());
}
}
}
action.complete(result, from);
主要看action.complete(result, from);
之前我们在把任务加入dispatcher的时候，new了一个ImageViewAction，ImageViewAction继承自Action
查看Action的继承，有很多子类
我们最开始设置的是ImageView，我们看看ImageViewAction的complete实现
ImageViewAction(Picasso picasso, ImageView imageView, Request data, int memoryPolicy,
int networkPolicy, int errorResId, Drawable errorDrawable, String key, Object tag,
Callback callback, boolean noFade) {
super(picasso, imageView, data, memoryPolicy, networkPolicy, errorResId, errorDrawable, key,
tag, noFade);
this.callback = callback;
}
@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();
}
}
重点看这一句
PicassoDrawable.setBitmap(target, context, result, from, noFade, indicatorsEnabled);
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);
}
target.setImageDrawable(drawable);
这个target就是我们的ImageView
好了，到这里，我们终于把我们的Bitmap转换成PicassoDrawable，PicassoDrawable继承自BitmapDrawable，最后塞给ImageView了，
如果这里不是ImageView，流程也都大体相似，
如果我们在调用picasso的into方法时，传入的时一个target实现类，最终会通过调用Target的onBitmaoLoaded方法完成图片的加载