（拾起.笔记）源码分析记录之Glide源码分析（一）
写在前面
这篇文章是个人参考源码及博客编写的笔记，主要是对源码简单分析。都是个人对源码的见解记录下来，只是介绍流程，供个人参考，如有需要阅读的，建议对源码和本文进行对照分析或者打开两个界面，以免翻车。文章有点长。
开始：
分析Glide版本：compile 'com.github.bumptech.glide:glide:3.7.0'
查看源码时请对应版本，以免混乱
Glide.with(context).load(url).into(imageView);
上面就是Glide API调用最基本的的流程
点进去Glide 就会看到with方法中会有四个方法，其中的参数又Activity 、context 、fragmentActivity、application
Q1
这里使用的是Activity为参数传递进去
public static RequestManager with(Activity activity) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(activity);
}
在with方法中可以接收五种不同的参数，看下图
444.png
这里只需要对参数为activity情况下进行分析，
RequestManagerRetriever.get() 获取一个RequestManagerRetriever 对象之后，调用get(activity)方法，然后将RequestManagerRetriever
Q2 get(Activity)。
public RequestManager get(Activity activity) {
//判断是否是后台线程，也就是是否在UI线程
if (Util.isOnBackgroundThread() || Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
android.app.FragmentManager fm = activity.getFragmentManager();
return fragmentGet(activity, fm);
}
}
前面的判断是在判断是否是后台线程，否则为UI线程，如果后台线程，就传入一个application上下文，然后进入到else方法中。先确保它还没销毁（assertNotDestroyed），再调用activity.getFragmentManager()通过activity获取一个Fragment的管理器，然后做为参数传入到fragmentGet(activity, fm) 方法中。
Q3
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
RequestManager fragmentGet(Context context, android.app.FragmentManager fm) {
RequestManagerFragment current = getRequestManagerFragment(fm);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
current.setRequestManager(requestManager);
}
return requestManager;
}
RequestManagerFragment 是继承于fragment，也就是说RequestManagerFragment 其实就是一个
fragment，自定义该类的其实就是在里面创建一个ActivityFragmentLifecycle，并将它的生命周期和
fragment相关联起来；
getRequestManagerFragment（fm）就是创建一个RequestManagerFragment
Q4
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
RequestManagerFragment getRequestManagerFragment(final android.app.FragmentManager fm) {
RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
if (current == null) {
current = pendingRequestManagerFragments.get(fm);
if (current == null) {
current = new RequestManagerFragment();
pendingRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
在创建RequestManagerFragment 的时候，它是通过findFragmentByTag来获取，如果没有就又从
保存的队列里面获取，再没有就new出一个，然后保存入Map中，在添加到FragmentManager中，然后发送一条handle消息，再将RequestManagerFragment返回
我们回到Q3中
在getRequestManagerFragment的时候，如果不是new出来一个新的RequestManager 就不会为空，否则它也会去创建一个RequestManager 并将生命周期的监听和树节点，并将RequestManager 设置到getRequestManagerFragment中去再将RequestManager
这里with的一系列源码已经解析完成了。其主要的目的就是创建一个fragment并且监听绑定它的生命周期变换，以免在glide在图片请求的时候，做一系列的停止等操作。
with方法就是通过监听fragment生命周期对图片进行操作，比如说暂停加载等
接下来就load()
因为with的时候返回的是RequestManager ，所以load就是RequestManager 的方法
在Request有多个load方法
111.png
其中包括byte数组、file、uri等等，说明Glide 可以接收多种类型的请求，这里我们对load(String)进行分析
Q5
public DrawableTypeRequest<String> load(String string) {
return (DrawableTypeRequest<String>) fromString().load(string);
}
这个方法会返回一个DrawableTypeRequest类型，并指定它的泛型是String，然后调用
fromString() 再调用load(String)
进去看看fromString
Q6
public DrawableTypeRequest<String> fromString() {
return loadGeneric(String.class);
}
private <T> DrawableTypeRequest<T> loadGeneric(Class<T> modelClass) {
ModelLoader<T, InputStream> streamModelLoader= Glide.buildStreamModelLoader(modelClass, context);
ModelLoader<T, ParcelFileDescriptor> fileDescriptorModelLoader =
Glide.buildFileDescriptorModelLoader(modelClass, context);
....
return optionsApplier.apply(new DrawableTypeRequest<T>(modelClass, streamModelLoader, fileDescriptorModelLoader, context,glide, requestTracker, lifecycle, optionsApplier));
}
这个方法很短，调用Glide.buildStreamModelLoader(modelClass, context) 和 Glide.buildFileDescriptorModelLoader(modelClass, context)都返回一个ModelLoader对象。这里我们只要知道 ModelLoader 接口是加载图片的就好，因为里面过于复杂，不做过多介绍。他会根据你传入的参数类型返回相应的对象，我们在fromString方法传入的是String.class，所以这里会返回StreamStringLoader。最后一行会new 一个 DrawableTypeRequest 将 modelClass,StreamStringLoader等参数传进去,并将其返回。
Q7
222.png
进入到该类,其他的我们先不要注意，你会发现该类中有asGif()，asBitmap()，这个就是我们在强制指定加载静态图片和动态图片，看看它的方法
Q8
public BitmapTypeRequest<ModelType> asBitmap() {
return optionsApplier.apply(new BitmapTypeRequest<ModelType>(this, streamModelLoader,fileDescriptorModelLoader, optionsApplier));
}
public GifTypeRequest<ModelType> asGif() {
return optionsApplier.apply(new GifTypeRequest<ModelType>(this, streamModelLoader, optionsApplier));
}
源码看出，如果指定了asBitmap()或者asGif()，默认的会使用DrawableTypeRequest，使用fromString()就返回一个DrawableTypeRequest,再来Q5 中的load(Stirng),点进去直接跳到DrawableTypeRequest的父类DrawableRequestBuilder。
Q9
@Override
public DrawableRequestBuilder<ModelType> load(ModelType model) {
super.load(model);
return this;
}
public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> load(ModelType model) {
this.model = model;
isModelSet = true;
return this;
}
只是简单的赋值并返回this，看看它的全部方法
333.png
回发现，我们在调用api的时候，使用的方法大都在这个类中。致此load已经分析好了
看一下into,这个方法较为复杂，这里只分析主线，对于分岔路可以自行去分析。
在load分析的DrawableRequestBuilder类方法的截图中，你会看到一个into(),这个就是into的入口
进去看看：
Q10
public Target<TranscodeType> into(ImageView view) {
Util.assertMainThread();
if (view == null) {
throw new IllegalArgumentException("You must pass in a non null View");
}
if (!isTransformationSet && view.getScaleType() != null) {
switch (view.getScaleType()) {
case CENTER_CROP:
applyCenterCrop();
break;
case FIT_CENTER:
case FIT_START:
case FIT_END:
applyFitCenter();
break;
//$CASES-OMITTED$
default:
// Do nothing.
}
}
return into(glide.buildImageViewTarget(view, transcodeClass));
}
前面一些代码先不用管，我们先注意一下最后一行代码，into(glide.buildImageViewTarget(view, transcodeClass)); 在into当中调用glide.buildImageViewTarget(view, transcodeClass)，老规矩，进去看看
Q11
<R> Target<R> buildImageViewTarget(ImageView imageView, Class<R> transcodedClass) {
return imageViewTargetFactory.buildTarget(imageView, transcodedClass);
}
紧接的是调用一个buildTarget
Q12
public <Z> Target<Z> buildTarget(ImageView view, Class<Z> clazz) {
if (GlideDrawable.class.isAssignableFrom(clazz)) {
return (Target<Z>) new GlideDrawableImageViewTarget(view);
} else if (Bitmap.class.equals(clazz)) {
return (Target<Z>) new BitmapImageViewTarget(view);
} else if (Drawable.class.isAssignableFrom(clazz)) {
return (Target<Z>) new DrawableImageViewTarget(view);
} else {
throw new IllegalArgumentException("Unhandled class: " + clazz
+ ", try .as*(Class).transcode(ResourceTranscoder)");
}
}
这里会根据class来判断要创建哪个对象，这里我们只需要知道会返回一个 GlideDrawableImageViewTarget对象，因为如果要分析其class的话，还要需要很大的功夫，这里我们只关心主线，返回GlideDrawableImageViewTarget，我们回到Q10中的最后一行代码，into(GlideDrawableImageViewTarget),
Q13
public <Y extends Target<TranscodeType>> Y into(Y target) {
Util.assertMainThread();
if (target == null) {
throw new IllegalArgumentException("You must pass in a non null Target");
}
if (!isModelSet) {
throw new IllegalArgumentException("You must first set a model (try #load())");
}
Request previous = target.getRequest();
if (previous != null) {
previous.clear();
requestTracker.removeRequest(previous);
previous.recycle();
}
Request request = buildRequest(target);
target.setRequest(request);
lifecycle.addListener(target);
requestTracker.runRequest(request);
return target;
}
其中target.getRequest()是获取当前的taget是否有请求，如果存在就将它清空回收，然后在重新创建一个Request请求对象，也就是调用huildRequest(target),
我们看看 buildRequest(target)方法，会返回一个Request类型，
Q14
private Request buildRequest(Target<TranscodeType> target) {
if (priority == null) {
priority = Priority.NORMAL;
}
return buildRequestRecursive(target, null);
}
再调用buildRequestRecursive 把 GlideDrawableImageViewTarget 和 null 丢进去
Q15
private Request buildRequestRecursive(Target<TranscodeType> target, ThumbnailRequestCoordinator parentCoordinator) {
.....
} else {
// Base case: no thumbnail.
return obtainRequest(target, sizeMultiplier, priority, parentCoordinator);
}
}
主要看最后一行 obtainRequest(target, sizeMultiplier, priority, parentCoordinator);
Q16
private Request obtainRequest(Target<TranscodeType> target, float sizeMultiplier, Priority priority,RequestCoordinator requestCoordinator) {
return GenericRequest.obtain(
loadProvider,
model,
signature,
context,
priority,
target,
sizeMultiplier,
placeholderDrawable,
placeholderId,
errorPlaceholder,
errorId,
fallbackDrawable,
fallbackResource,
requestListener,
requestCoordinator,
glide.getEngine(),
transformation,
transcodeClass,
isCacheable,
animationFactory,
overrideWidth,
overrideHeight,
diskCacheStrategy);
}
紧接的会将一些乱七八糟的参数传入到 GenericRequest.obtain(..)方法中
Q17
public static <A, T, Z, R> GenericRequest<A, T, Z, R> obtain(....) {
@SuppressWarnings("unchecked")
GenericRequest<A, T, Z, R> request = (GenericRequest<A, T, Z, R>) REQUEST_POOL.poll();
if (request == null) {
request = new GenericRequest<A, T, Z, R>();
}
request.init(loadProvider,
model,
signature,
context,
priority,
target,
sizeMultiplier,
placeholderDrawable,
placeholderResourceId,
errorDrawable,
errorResourceId,
fallbackDrawable,
fallbackResourceId,
requestListener,
requestCoordinator,
engine,
transformation,
transcodeClass,
isMemoryCacheable,
animationFactory,
overrideWidth,
overrideHeight,
diskCacheStrategy);
return request;
}
这里会调用request = new GenericRequest<A, T, Z, R>() 创建出一个GenericRequest对象，并将这些乱七八糟的参数传进来，并返回GenericRequest，其中很多的参数我们都是比较熟悉的，像什么placeholderId、errorPlaceholder、diskCacheStrategy等等，这里可以看出，刚才在GenericRequestBuilder中设置的参数都会封装到此处来，也就是Glide的API,所以在Q13中的buildRequest(target); 返回来的Request对象，其实就是GenericRequest，GenericRequest里面封装这api中的属性值。
接下来我们回到Q13中，看看这个方法 requestTracker.runRequest(request) ，调用runRequest将GenericRequest传递过去，来看看runRequest方法
Q18
public void runRequest(Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
这里判断Glide状态是否为停止的状态，然后调用GenericRequest的begin() 方法，否则将Request添加到待执行队列，所以我们进去看看GenericRequest的begin方法
Q19
@Override
public void begin() {
startTime = LogTime.getLogTime();
if (model == null) {
onException(null);
return;
}
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
我们先看看onException(null) ，先判断model是否为空，mode就是在Q9 中 load传过来的String,也就是uri，也就是说uri为空的时候，就会调用onException方法，进去看看
Q20
@Override
public void onException(Exception e) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "load failed", e);
}
status = Status.FAILED;
//TODO: what if this is a thumbnail request?
if (requestListener == null || !requestListener.onException(e, model, target, isFirstReadyResource())) {
setErrorPlaceholder(e);
}
}
经过一系列的判断后，会调用setErrorPlaceholder(e),看名字就知道，他就是用来设置占位符的，也就是错误图片
Q21
private void setErrorPlaceholder(Exception e) {
if (!canNotifyStatusChanged()) {
return;
}
Drawable error = model == null ? getFallbackDrawable() : null;
if (error == null) {
error = getErrorDrawable();
}
if (error == null) {
error = getPlaceholderDrawable();
}
target.onLoadFailed(e, error);
}
这里判断error是否为空之后，就会获取一个error图片，还是没有的话再获取一个placeholder图片
然后调用target.onLoadFailed(e, error) 这个tagat就是Q11 和Q12中的GlideDrawableImageViewTarget ，进去之后onLoadFailed()是在它父类ImageViewTarget中
Q22
@Override
public void onLoadFailed(Exception e, Drawable errorDrawable) {
view.setImageDrawable(errorDrawable);
}
只是将Drawable 设置进ImageView中去。onExption()方法就是这样,所以我们接下来回到Q19 对下面就行分析，
Q23
@Override
public void begin() {
startTime = LogTime.getLogTime();
if (model == null) {
onException(null);
return;
}
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
}
if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
}
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
}
}
这里会调用到onSizeReady() 方法，这个宽高是自定义的宽高，是通过一系列的运算之后得到的宽高，点击进去看看这个方法，
Q24
@Override
public void onSizeReady(int width, int height) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("Got onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
if (status != Status.WAITING_FOR_SIZE) {
return;
}
status = Status.RUNNING;
width = Math.round(sizeMultiplier * width);
height = Math.round(sizeMultiplier * height);
ModelLoader<A, T> modelLoader = loadProvider.getModelLoader();
final DataFetcher<T> dataFetcher = modelLoader.getResourceFetcher(model, width, height);
if (dataFetcher == null) {
onException(new Exception("Failed to load model: \'" + model + "\'"));
return;
}
ResourceTranscoder<Z, R> transcoder = loadProvider.getTranscoder();
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished setup for calling load in " + LogTime.getElapsedMillis(startTime));
}
loadedFromMemoryCache = true;
loadStatus = engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder,
priority, isMemoryCacheable, diskCacheStrategy, this);
loadedFromMemoryCache = resource != null;
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished onSizeReady in " + LogTime.getElapsedMillis(startTime));
}
}
这时会看到一个loadProvider.getModeLoader()方法,在同getModeLoader之后获取到一个ModeLoader对象在调用它的getResource(model,width,height);方法获取到一个DataFetcher对象，这里先去了解一下loadProvider.getModeLoader()的方法，这个loadProvider其实就是分析load()方法的时候进行初始化的，我们回到在Q6 中在loadGeneric的时候，会创建出一个DrawableTypeRequest，在构造方法的时候，会调用super方法，super方法的第三个参数当中需要传入一个LoadProvider 对象，然后就会调用buildProvider加载出一个LoadProvider对象，想看看这个类
Q25
public class DrawableTypeRequest<ModelType> extends DrawableRequestBuilder<ModelType> implements DownloadOptions {
private final ModelLoader<ModelType, InputStream> streamModelLoader;
private final ModelLoader<ModelType, ParcelFileDescriptor> fileDescriptorModelLoader;
private final RequestManager.OptionsApplier optionsApplier;
private static <A, Z, R> FixedLoadProvider<A, ImageVideoWrapper, Z, R> buildProvider(Glide glide,
ModelLoader<A, InputStream> streamModelLoader,
ModelLoader<A, ParcelFileDescriptor> fileDescriptorModelLoader, Class<Z> resourceClass,Class<R> transcodedClass,ResourceTranscoder<Z, R> transcoder) {
if (streamModelLoader == null && fileDescriptorModelLoader == null) {
return null;
}
if (transcoder == null) {
transcoder = glide.buildTranscoder(resourceClass, transcodedClass);
}
DataLoadProvider<ImageVideoWrapper, Z> dataLoadProvider = glide.buildDataProvider(ImageVideoWrapper.class,resourceClass);
ImageVideoModelLoader<A> modelLoader = new ImageVideoModelLoader<A>(streamModelLoader,fileDescriptorModelLoader);
return new FixedLoadProvider<A, ImageVideoWrapper, Z, R>(modelLoader, transcoder, dataLoadProvider);
}
DrawableTypeRequest(Class<ModelType> modelClass, ModelLoader<ModelType, InputStream> streamModelLoader,ModelLoader<ModelType, ParcelFileDescriptor> fileDescriptorModelLoader, Context context, Glide glide,RequestTracker requestTracker, Lifecycle lifecycle, RequestManager.OptionsApplier optionsApplier) {
super(context, modelClass,
buildProvider(glide, streamModelLoader, fileDescriptorModelLoader, GifBitmapWrapper.class,
GlideDrawable.class, null),
glide, requestTracker, lifecycle);
this.streamModelLoader = streamModelLoader;
this.fileDescriptorModelLoader = fileDescriptorModelLoader;
this.optionsApplier = optionsApplier;
}
public BitmapTypeRequest<ModelType> asBitmap() {
return optionsApplier.apply(new BitmapTypeRequest<ModelType>(this, streamModelLoader,
fileDescriptorModelLoader, optionsApplier));
}
public GifTypeRequest<ModelType> asGif() {
return optionsApplier.apply(new GifTypeRequest<ModelType>(this, streamModelLoader, optionsApplier));
}
}
先看看 transcoder = glide.buildTranscoder(resourceClass, transcodedClass),这里你只要知道会返回一个ResourceTranscoder的子类GifBitmapWrapperDrawableTranscoder对象，它是用于对图片进行转码，紧接的就是glide.buildDataProvider(ImageVideoWrapper.class， resourceClass) 构建一个DataLoadProvider，这里你也需要只知道它是创建一个ImageVideoGifDrawableLoadProvider
对象，再接的就是new ImageVideoModelLoader 将在Q6 中构建的ModelLoade封装进去，最后就是通过 new FixedLoadProvider<A, ImageVideoWrapper, Z, R>(modelLoader, transcoder, dataLoadProvider); 将ImageVideoModelLoader，GifBitmapWrapperDrawableTranscoder，ImageVideoGifDrawableLoadProvider封装进去，所以在Q24中的loadProvider其实就是FixedLoadProvider，也就是说loadProvider.getModelLoader()获取的就是封装进去的ImageVideoModelLoader，接下来回到Q24中，会通过ImagVideoModelLoader对象调用这个modelLoader.getResourceFetcher(model, width, height)方法获取到一个DataFetcher对象，进去看看ImagVideoModelLoader这个类
Q26
public class ImageVideoModelLoader<A> implements ModelLoader<A, ImageVideoWrapper> {
private static final String TAG = "IVML";
private final ModelLoader<A, InputStream> streamLoader;
private final ModelLoader<A, ParcelFileDescriptor> fileDescriptorLoader;
public ImageVideoModelLoader(ModelLoader<A, InputStream> streamLoader,
ModelLoader<A, ParcelFileDescriptor> fileDescriptorLoader) {
if (streamLoader == null && fileDescriptorLoader == null) {
throw new NullPointerException("At least one of streamLoader and fileDescriptorLoader must be non null");
}
this.streamLoader = streamLoader;
this.fileDescriptorLoader = fileDescriptorLoader;
}
@Override
public DataFetcher<ImageVideoWrapper> getResourceFetcher(A model, int width, int height) {
DataFetcher<InputStream> streamFetcher = null;
if (streamLoader != null) {
streamFetcher = streamLoader.getResourceFetcher(model, width, height);
}
DataFetcher<ParcelFileDescriptor> fileDescriptorFetcher = null;
if (fileDescriptorLoader != null) {
fileDescriptorFetcher = fileDescriptorLoader.getResourceFetcher(model, width, height);
}
if (streamFetcher != null || fileDescriptorFetcher != null) {
return new ImageVideoFetcher(streamFetcher, fileDescriptorFetcher);
} else {
return null;
}
}
static class ImageVideoFetcher implements DataFetcher<ImageVideoWrapper> {
private final DataFetcher<InputStream> streamFetcher;
private final DataFetcher<ParcelFileDescriptor> fileDescriptorFetcher;
public ImageVideoFetcher(DataFetcher<InputStream> streamFetcher,
DataFetcher<ParcelFileDescriptor> fileDescriptorFetcher) {
this.streamFetcher = streamFetcher;
this.fileDescriptorFetcher = fileDescriptorFetcher;
}
}
@SuppressWarnings("resource")
// @see ModelLoader.loadData
@Override
public ImageVideoWrapper loadData(Priority priority) throws Exception {
InputStream is = null;
if (streamFetcher != null) {
try {
is = streamFetcher.loadData(priority);
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception fetching input stream, trying ParcelFileDescriptor", e);
}
if (fileDescriptorFetcher == null) {
throw e;
}
}
}
ParcelFileDescriptor fileDescriptor = null;
if (fileDescriptorFetcher != null) {
try {
fileDescriptor = fileDescriptorFetcher.loadData(priority);
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception fetching ParcelFileDescriptor", e);
}
if (is == null) {
throw e;
}
}
}
return new ImageVideoWrapper(is, fileDescriptor);
}
}
看看getResourceFetcher方法中，获取一个streamFetcher ，streamLoader就是我们在loadGeneric（）方法中创建的StreamStringLoader，调用他的getResourceFetcher就是得到一个HttpUrlFetcher，后面就是new ImageVideoFetcher 将HttpUrlFetcher和StreamStringLoader传进去，所以，我们在Q24得到的DataFetcher其实就是这个ImageVideoFetcher ，回到Q24中，接下来就是调用 engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder,priority, isMemoryCacheable, diskCacheStrategy, this) 其中dataFetcher
就是我们的ImageVideoFetcher,loadProvider就是 Q24中的FixedLoadProvider，transcoder就是FixedLoadProvider中的GifBitmapWrapperDrawableTranscoder,其中还包括是否开启内存缓存，硬盘缓存策略，还有一个this,这个this就是ResourceCallback接口，这个接口GenericRequest已经实现，然后就是engine中的load方法，
Q26.1
public <T, Z, R> LoadStatus load(....) {
.....
EngineJob engineJob = engineJobFactory.build(key, isMemoryCacheable);
DecodeJob<T, Z, R> decodeJob = new DecodeJob<T, Z, R>(key, width, height, fetcher, loadProvider, transformation,transcoder, diskCacheProvider, diskCacheStrategy, priority);
EngineRunnable runnable = new EngineRunnable(engineJob, decodeJob, priority);
jobs.put(key, engineJob);
engineJob.addCallback(cb);
engineJob.start(runnable);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new LoadStatus(cb, engineJob);
}
看到一个engineJobFactory.build(...）其实就是创建一个EngineJob 对象，它是用来开启线程的，为后面的异步加载图片做准备。然后就是DecodeJob对象，是用来给是图片进行解码的。
还有一个EngineRunnable，看名字就知道的，它是一个Runnable的子类，任何将DecodeJob，EngineJob 传进去，所以看看它的run方法，
Q27
@Override
public void run() {
if (isCancelled) {
return;
}
Exception exception = null;
Resource<?> resource = null;
try {
resource = decode();
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception decoding", e);
}
exception = e;
}
if (isCancelled) {
if (resource != null) {
resource.recycle();
}
return;
}
if (resource == null) {
onLoadFailed(exception);
} else {
onLoadComplete(resource);
}
}
这个run方法一旦运行，就说明它是在子线程中运行了，其中里面包括一个decode（）方法
Q28
private Resource<?> decode() throws Exception {
if (isDecodingFromCache()) {
return decodeFromCache();
} else {
return decodeFromSource();
}
}
这里会判断它是否是从缓存中去解码图片就会调用decodeFromCache，否则就调用decodeFromSource，我们先看看decodeFromSource方法，
Q29
private Resource<?> decodeFromSource() throws Exception {
return decodeJob.decodeFromSource();
}
接着他会调用DecodeJob对象中的decodeFromSource方法，
Q30
public Resource<Z> decodeFromSource() throws Exception {
Resource<T> decoded = decodeSource();
return transformEncodeAndTranscode(decoded);
}
接着就是再调用decodeSource() 获取一个Resource对象，再调用transformEncodeAndTranscode（）将Resource对象传进去处理，再返回一个Resource对象。先进入到decodeSource中，
Q31
private Resource<T> decodeSource() throws Exception {
Resource<T> decoded = null;
try {
long startTime = LogTime.getLogTime();
final A data = fetcher.loadData(priority);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Fetched data", startTime);
}
if (isCancelled) {
return null;
}
decoded = decodeFromSourceData(data);
} finally {
fetcher.cleanup();
}
return decoded;
}
注意到一个方法，fetcher.loadData(priority)，返回一个A，这个fercher就是在Q24、25、26中通过
ImagVideoModelLoader得到一个ImageVideoFetcher对象，再来调用他的loadData方法，所以进去瞧一瞧
Q32
@Override
public ImageVideoWrapper loadData(Priority priority) throws Exception {
InputStream is = null;
if (streamFetcher != null) {
try {
is = streamFetcher.loadData(priority);
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception fetching input stream, trying ParcelFileDescriptor", e);
}
if (fileDescriptorFetcher == null) {
throw e;
}
}
}
ParcelFileDescriptor fileDescriptor = null;
if (fileDescriptorFetcher != null) {
try {
fileDescriptor = fileDescriptorFetcher.loadData(priority);
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception fetching ParcelFileDescriptor", e);
}
if (is == null) {
throw e;
}
}
}
return new ImageVideoWrapper(is, fileDescriptor);
}
就在这里，InputStream is = streamFetcher.loadData(priority); 这货返回一个InputStream 对象，也就是说streamFetcher.loadData(priority)就是请求数据返回来的图片流，这个streamFetcher就是在Q26 中new ImageVideoFetcher时传的HttpUrlFetcher和StreamStringLoader中的HttpUrlFetcher，所以这个streamFetcher.loadData(priority)就是调用HttpUrlFetcher中的loadData方法，看看呗
Q33
@Override
public InputStream loadData(Priority priority) throws Exception {
return loadDataWithRedirects(glideUrl.toURL(), 0 /*redirects*/, null /*lastUrl*/, glideUrl.getHeaders());
}
private InputStream loadDataWithRedirects(URL url, int redirects, URL lastUrl, Map<String, String> headers)throws IOException {
if (redirects >= MAXIMUM_REDIRECTS) {
throw new IOException("Too many (> " + MAXIMUM_REDIRECTS + ") redirects!");
} else {
// Comparing the URLs using .equals performs additional network I/O and is generally broken.
// See http://michaelscharf.blogspot.com/2006/11/javaneturlequals-and-hashcode-make.html.
try {
if (lastUrl != null && url.toURI().equals(lastUrl.toURI())) {
throw new IOException("In re-direct loop");
}
} catch (URISyntaxException e) {
// Do nothing, this is best effort.
}
}
urlConnection = connectionFactory.build(url);
for (Map.Entry<String, String> headerEntry : headers.entrySet()) {
urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue());
}
urlConnection.setConnectTimeout(2500);
urlConnection.setReadTimeout(2500);
urlConnection.setUseCaches(false);
urlConnection.setDoInput(true);
// Connect explicitly to avoid errors in decoders if connection fails.
urlConnection.connect();
if (isCancelled) {
return null;
}
final int statusCode = urlConnection.getResponseCode();
if (statusCode / 100 == 2) {
return getStreamForSuccessfulRequest(urlConnection);
} else if (statusCode / 100 == 3) {
String redirectUrlString = urlConnection.getHeaderField("Location");
if (TextUtils.isEmpty(redirectUrlString)) {
throw new IOException("Received empty or null redirect url");
}
URL redirectUrl = new URL(url, redirectUrlString);
return loadDataWithRedirects(redirectUrl, redirects + 1, url, headers);
} else {
if (statusCode == -1) {
throw new IOException("Unable to retrieve response code from HttpUrlConnection.");
}
throw new IOException("Request failed " + statusCode + ": " + urlConnection.getResponseMessage());
}
}
这些就是网络请求，返回一个InputStream 对象，回到Q32中，最后一行的new ImageVideoWrapper(is, fileDescriptor)，返回一个ImageVideoWrapper对象，然后将InputStream 封装进去，所以在Q31中的A 类型就是ImageVideoWrapper对象，Q31 DecodeJob.decodeSource中的final A data = fetcher.loadData(priority)分析完了，在回头看看Q31中，看这一行，decoded = decodeFromSourceData(data)，将ImageVideoWrapper对象传进去
Q34
private Resource<T> decodeFromSourceData(A data) throws IOException {
final Resource<T> decoded;
if (diskCacheStrategy.cacheSource()) {
decoded = cacheAndDecodeSourceData(data);
} else {
long startTime = LogTime.getLogTime();
decoded = loadProvider.getSourceDecoder().decode(data, width, height);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded from source", startTime);
}
}
return decoded;
}
注意这个 decoded = loadProvider.getSourceDecoder().decode(data, width, height);这个方法，loadProvider就是FixedLoadProvider,在Q25中有解释，调用他的getSourceDecoder()获取到他在构造的时候传进去的ImageVideoGifDrawableLoadProvider对象，在调用它在构造方法中创建的GifBitmapWrapperResourceDecoder对象，再调用GifBitmapWrapperResourceDecoder的decode方法，
Q35
@SuppressWarnings("resource")
// @see ResourceDecoder.decode
@Override
public Resource<GifBitmapWrapper> decode(ImageVideoWrapper source, int width, int height) throws IOException {
ByteArrayPool pool = ByteArrayPool.get();
byte[] tempBytes = pool.getBytes();
GifBitmapWrapper wrapper = null;
try {
wrapper = decode(source, width, height, tempBytes);
} finally {
pool.releaseBytes(tempBytes);
}
return wrapper != null ? new GifBitmapWrapperResource(wrapper) : null;
}
再调用它的decode重载方法
Q36
private GifBitmapWrapper decode(ImageVideoWrapper source, int width, int height, byte[] bytes) throws IOException {
final GifBitmapWrapper result;
if (source.getStream() != null) {
result = decodeStream(source, width, height, bytes);
} else {
result = decodeBitmapWrapper(source, width, height);
}
return result;
}
判断source是否为空，sourcek就是ImageVideoWrapper，也就是刚才的A类型，传入到decodeFromSourceData(data)方法，而这个ImageVideoWrapper是持有InputStream对象的，是有这里不等于空，则调用decodeStream,
Q37
private GifBitmapWrapper decodeStream(ImageVideoWrapper source, int width, int height, byte[] bytes)throws IOException {
InputStream bis = streamFactory.build(source.getStream(), bytes);
bis.mark(MARK_LIMIT_BYTES);
ImageHeaderParser.ImageType type = parser.parse(bis);
bis.reset();
GifBitmapWrapper result = null;
if (type == ImageHeaderParser.ImageType.GIF) {
result = decodeGifWrapper(bis, width, height);
}
// Decoding the gif may fail even if the type matches.
if (result == null) {
// We can only reset the buffered InputStream, so to start from the beginning of the stream, we need to
// pass in a new source containing the buffered stream rather than the original stream.
ImageVideoWrapper forBitmapDecoder = new ImageVideoWrapper(bis, source.getFileDescriptor());
result = decodeBitmapWrapper(forBitmapDecoder, width, height);
}
return result;
}
这里先判断是否为GIF，是就调用decodeGifWrapper(bis, width, height)，否则会创建一个ImageVideoWrapper 对象，调用decodeBitmapWrapper(forBitmapDecoder, width, height)传进去，所以加载普通图片就先进入到decodeBitmapWrapper方法中
Q38
private GifBitmapWrapper decodeBitmapWrapper(ImageVideoWrapper toDecode, int width, int height) throws IOException {
GifBitmapWrapper result = null;
Resource<Bitmap> bitmapResource = bitmapDecoder.decode(toDecode, width, height);
if (bitmapResource != null) {
result = new GifBitmapWrapper(bitmapResource, null);
}
return result;
}
通过调用 bitmapDecoder.decode(toDecode, width, height) 返回一个Resource对象，再将它封装到GifBitmapWrapper中，这个ditmapDecoder我们只要知道是一个 ImageVideoBitmapDecoder对象，我们只要往主线走，我们看一下他的方法，
Q39
@Override
public Resource<Bitmap> decode(ImageVideoWrapper source, int width, int height) throws IOException {
Resource<Bitmap> result = null;
InputStream is = source.getStream();
if (is != null) {
try {
result = streamDecoder.decode(is, width, height);
} catch (IOException e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Failed to load image from stream, trying FileDescriptor", e);
}
}
}
if (result == null) {
ParcelFileDescriptor fileDescriptor = source.getFileDescriptor();
if (fileDescriptor != null) {
result = fileDescriptorDecoder.decode(fileDescriptor, width, height);
}
}
return result;
}
在获取到ImageVideoWrapper 中的InputStream，之后再调用streamDecoder.decode(is, width, height);获取一个Resource<Bitmap> 泛型为Bitmap，这个streamDecoder只需要知道他是StreamBitmapDecoder对象，再来看看他的decode方法，
Q40
@Override
public Resource<Bitmap> decode(InputStream source, int width, int height) {
Bitmap bitmap = downsampler.decode(source, bitmapPool, width, height, decodeFormat);
return BitmapResource.obtain(bitmap, bitmapPool);
}
然后。。它又去调用 downsampler.decode(source, bitmapPool, width, height, decodeFormat) 返回一个Bitmap对象，再封装到Resource中，downsampler就是Downsampler，里面主要是将InputStream 处理得到一个Bitmap对象，再是用BitmapResource将其封装，
Q41
public static BitmapResource obtain(Bitmap bitmap, BitmapPool bitmapPool) {
if(bitmap == null) {
return null;
}else{
return new BitmapResource(bitmap, bitmapPool);
}
}
是的，就是new 一个BitmapResource,所以得出，在Q38中streamDecoder.decode(is, width, height)方法中获取的就是一个BitmapResourced对象，然后在将BitmapResource对象封装到GifBitmapWrapper方法中，然后返回一步一步向上返回GifBitmapWrapper，Q38 到 Q37 到Q36 到Q35 ，那回到 Q35
@Override
public Resource<GifBitmapWrapper> decode(ImageVideoWrapper source, int width, int height) throws IOException {
ByteArrayPool pool = ByteArrayPool.get();
byte[] tempBytes = pool.getBytes();
GifBitmapWrapper wrapper = null;
try {
wrapper = decode(source, width, height, tempBytes);
} finally {
pool.releaseBytes(tempBytes);
}
return wrapper != null ? new GifBitmapWrapperResource(wrapper) : null;
}
最后一行又创建了一次GifBitmapWrapperResource对GifBitmapWrapper进行封装，然后将GifBitmapWrapperResource返回到Q34 ，GifBitmapWrapperResource是继承自Resource，所以将这个GifBitmapWrapperResource返回到Q34,再到Q31,然后在到Q30
到Q30 看看，我们刚刚就是分析的decodeSource，返回一个GifBitmapWrapperResource(wrapper) ，将GifBitmapWrapperResource 传入到transformEncodeAndTranscode方法中
public Resource<Z> decodeFromSource() throws Exception {
Resource<T> decoded = decodeSource();
return transformEncodeAndTranscode(decoded);
}
transformEncodeAndTranscode方法的返回值也是一个Resource对象，不过他的泛型是不一样的，一个Z 一个T，先看看这个方法吧
Q42
private Resource<Z> transformEncodeAndTranscode(Resource<T> decoded) {
long startTime = LogTime.getLogTime();
Resource<T> transformed = transform(decoded);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Transformed resource from source", startTime);
}
writeTransformedToCache(transformed);
startTime = LogTime.getLogTime();
Resource<Z> result = transcode(transformed);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Transcoded transformed from source", startTime);
}
return result;
}
注意到 Resource<Z> result = transcode(transformed) 这段代码，又调用trancode(transformed)来看看
Q43
private Resource<Z> transcode(Resource<T> transformed) {
if (transformed == null) {
return null;
}
return transcoder.transcode(transformed);
}
transcoder是在DecodeJob初始化的时候传来，初始化的时候是在Engine.load(Q26) 的方法中，而调用Engine.load是在GenericRequest的onSizeReady（Q24）中，通过loadProvider.getTranscoder()获取出来的
而这个loadProvider就是Q25中创建出来的 FixedLoadProvider并传入3个参数，而他获取getTranscoder()就是Q25中初始化传入的GifBitmapWrapperDrawableTranscoder，我们看一下GifBitmapWrapperDrawableTranscoder中的transcode方法
Q44
public Resource<GlideDrawable> transcode(Resource<GifBitmapWrapper> toTranscode) {
GifBitmapWrapper gifBitmap = toTranscode.get();
Resource<Bitmap> bitmapResource = gifBitmap.getBitmapResource();
final Resource<? extends GlideDrawable> result;
if (bitmapResource != null) {
result = bitmapDrawableResourceTranscoder.transcode(bitmapResource);
} else {
result = gifBitmap.getGifResource();
}
// This is unchecked but always safe, anything that extends a Drawable can be safely cast to a Drawable.
return (Resource<GlideDrawable>) result;
}
可以看到，它是先从GifBitmapWrapperResource中取出GifBitmapWrapper，再从GifBitmapWrapper中取出BitmapResource （Q38,39,40,41 有解释了)，然后判断是否为空之后调用bitmapDrawableResourceTranscoder.transcode(bitmapResource)，否则调用gifBitmap.getGifResource()方法加载一个gif图片。跟GifBitmapWrapperDrawableTranscoder一样，只需要知道这个bitmapDrawableResourceTranscoder是GlideBitmapDrawableTranscoder对象就可以了，否则分析会不完。所以接下来就会调用GlideBitmapDrawableTranscoder中的transcode方法将BitmapResource 传进去。
Q45
@Override
public Resource<GlideBitmapDrawable> transcode(Resource<Bitmap> toTranscode) {
GlideBitmapDrawable drawable = new GlideBitmapDrawable(resources, toTranscode.get());
return new GlideBitmapDrawableResource(drawable, bitmapPool);
}
这里面又做了两个动作，new GlideBitmapDrawable对象，并获取出BitmapResource 中的Bitmap封装到里面，在返回一个GlideBitmapDrawableResource，又把GlideBitmapDrawable传进去返回，所以Q44当中返回的就是GlideBitmapDrawableResource对象，返回的就是Resource<GlideBitmapDrawable>，Q42 中的这个Z就是GlideBitmapDrawable，所以我们回到Q44当中，这个Resource<? extends GlideDrawable> result 就是GlideBitmapDrawableResource<GlideBitmapDrawable> 将它返回到Q42 再返回到 Q30中再到Q27 (跨度又点大)，也就是回到EngineRunnable的run方法中。
@Override
public void run() {
if (isCancelled) {
return;
}
Exception exception = null;
Resource<?> resource = null;
try {
resource = decode();
} catch (Exception e) {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Exception decoding", e);
}
exception = e;
}
if (isCancelled) {
if (resource != null) {
resource.recycle();
}
return;
}
if (resource == null) {
onLoadFailed(exception);
} else {
onLoadComplete(resource);
}
}
这个 decode() 有够深的，decode返回的就是上面分析的Resource<GlideDrawable>，最后判断是否为空之后，调用onLoadComplete传进去，
Q46
private void onLoadComplete(Resource resource) {
manager.onResourceReady(resource);
}
这个manager就是Q26 传的EngineJob对象，看看呗
Q47
@Override
public void onResourceReady(final Resource<?> resource) {
this.resource = resource;
MAIN_THREAD_HANDLER.obtainMessage(MSG_COMPLETE, this).sendToTarget();
}
将 Resource<?> resource赋值给成员变量之后，发送一个消息，把自己传过去。Handler 就是EngineJob中的静态内部类，在run方法运行后就一直在子线程中执行上面分析的逻辑代码，只有在这里的时候才通过handler回到子线程当中来，所以可以猜到，接下来的代码就是执行图片展示的代码。
Q48
private static class MainThreadCallback implements Handler.Callback {
@Override
public boolean handleMessage(Message message) {
if (MSG_COMPLETE == message.what || MSG_EXCEPTION == message.what) {
EngineJob job = (EngineJob) message.obj;
if (MSG_COMPLETE == message.what) {
job.handleResultOnMainThread();
} else {
job.handleExceptionOnMainThread();
}
return true;
}
return false;
}
}
接下来就是调用 EngineJob 中的 handleResultOnMainThread方法，
Q49
private void handleResultOnMainThread() {
......
for (ResourceCallback cb : cbs) {
if (!isInIgnoredCallbacks(cb)) {
engineResource.acquire();
cb.onResourceReady(engineResource);
}
}
// Our request is complete, so we can release the resource.
engineResource.release();
}
看到一个for循环，遍历获取cbs,cbs是一个成员变量的集合private final List<ResourceCallback> cbs = new ArrayList<ResourceCallback>()，通过遍历获取到ResourceCallback ，那么ResourceCallback 添加是在什么时候的？在EngineJob的时候还有一个add的方法，
Q50
public void addCallback(ResourceCallback cb) {
Util.assertMainThread();
if (hasResource) {
cb.onResourceReady(engineResource);
} else if (hasException) {
cb.onException(exception);
} else {
cbs.add(cb);
}
}
最后就是cbs.add 将传进来的参数添加进集合中。这个addCallback方法就在Engine.load（Q26 ）中调用的，而且是作为load的参数传进来的，我们在Q24Q25的时候有分析过，在GenericRequst.onSizeReady()方法中我们调用engine.load时传入很多参数，在最后一个参数的时候会传入一个this，也就是GenericRequst的本身，也就是GenericRequst实现了ResourceCallback接口，所以EngineJob最终调用的就是GenericRequst的onResourceReady方法。
Q51
public void onResourceReady(Resource<?> resource) {
if (resource == null) {
onException(new Exception("Expected to receive a Resource<R> with an object of " + transcodeClass
+ " inside, but instead got null."));
return;
}
Object received = resource.get();
if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {
releaseResource(resource);
onException(new Exception("Expected to receive an object of " + transcodeClass
+ " but instead got " + (received != null ? received.getClass() : "") + "{" + received + "}"
+ " inside Resource{" + resource + "}."
+ (received != null ? "" : " "
+ "To indicate failure return a null Resource object, "
+ "rather than a Resource object containing null data.")
));
return;
}
if (!canSetResource()) {
releaseResource(resource);
// We can't set the status to complete before asking canSetResource().
status = Status.COMPLETE;
return;
}
onResourceReady(resource, (R) received);
}
先获取到resource.get() ，也就是上面分析的Q45 中的GlideBitmapDrawable， 再作为参数调用他的重载方法，
Q52
private void onResourceReady(Resource<?> resource, R result) {
// We must call isFirstReadyResource before setting status.
boolean isFirstResource = isFirstReadyResource();
status = Status.COMPLETE;
this.resource = resource;
if (requestListener == null || !requestListener.onResourceReady(result, model, target, loadedFromMemoryCache,isFirstResource)) {
GlideAnimation<R> animation = animationFactory.build(loadedFromMemoryCache, isFirstResource);
target.onResourceReady(result, animation);
}
notifyLoadSuccess();
}
这里只要看到他的 target.onResourceReady(result, animation)方法，target知道，也就是前面分析（Q12）中的封装ImageView的GlideDrawableImageViewTarget对象，调用它的onResourceReady方法
Q53
public void onResourceReady(GlideDrawable resource, GlideAnimation<? super GlideDrawable> animation) {
if (!resource.isAnimated()) {
//TODO: Try to generalize this to other sizes/shapes.
// This is a dirty hack that tries to make loading square thumbnails and then square full images less costly
// by forcing both the smaller thumb and the larger version to have exactly the same intrinsic dimensions.
// If a drawable is replaced in an ImageView by another drawable with different intrinsic dimensions,
// the ImageView requests a layout. Scrolling rapidly while replacing thumbs with larger images triggers
// lots of these calls and causes significant amounts of jank.
float viewRatio = view.getWidth() / (float) view.getHeight();
float drawableRatio = resource.getIntrinsicWidth() / (float) resource.getIntrinsicHeight();
if (Math.abs(viewRatio - 1f) <= SQUARE_RATIO_MARGIN
&& Math.abs(drawableRatio - 1f) <= SQUARE_RATIO_MARGIN) {
resource = new SquaringDrawable(resource, view.getWidth());
}
}
super.onResourceReady(resource, animation);
this.resource = resource;
resource.setLoopCount(maxLoopCount);
resource.start();
}
然后会调用父类的 super.onResourceReady(resource, animation);方法，
Q54
@Override
public void onResourceReady(Z resource, GlideAnimation<? super Z> glideAnimation) {
if (glideAnimation == null || !glideAnimation.animate(resource, this)) {
setResource(resource);
}
}
protected abstract void setResource(Z resource);
父类只是调用了它的 setResource 方法，而setResource 方法是一个抽象方法，所以它会调用自己的setResource 方法，
Q55
@Override
protected void setResource(GlideDrawable resource) {
view.setImageDrawable(resource);
}
这个view就是封装的ImageView,然后将GlideDrawable 设置进来，至此，一个图片就展示出来了。
总结：
本文只是简单的分析，供个人参考
