网上Glide源码解析的资料比较多，但鱼龙混杂，so我决定还是自己跟一遍源码吧，看源码真的是一件爆炸的事，好几次想放弃，但最后还是坚持下来了，唉。
首先先来捋一遍Glide的具体用法，从具体用法出发我们再来分析Glide内部都是怎么来实现这些方法的。
这是我从网上找来的Glide的主要功能示意图，这张图一目了然的显示了Glide能实现的功能。
功能示意图.png
先来看Glide最基础的图片加载用法：
Glide.with(context).load(url).into(imageView);
这里的load()方法就是指定要加载的图片资源，可以是网络图片，也可以是本地图片，资源图片，二进制流，Uri对象等等。
当然我们也可以在加载图片的基础上做很多事，比如设置缺省图，加载失败的时候显示的图，设置图片尺寸，加载动画等。。。就像这样：
Glide
.with(context)
.load(imageUrl)
.placeholder(R.mipmap.ic_launcher) //占位图
.error(R.mipmap.ic_launcher) //加载错误显示的图
.animate(R.anim.anim) //加载动画
.override(88, 88) //图片尺寸
.into(imageView);
这里都是采用多态形式来实现的。
Glide还可以指定要加载的图片格式。什么意思呢？就比如我这里有一个gif图片的图片链接地址，那我什么都不指定，用Glide加载，加载显示出来的就是gif图，但是如果我加了一个asBitmap()方法，指定加载的必须是静态图片，那么Glide就会只加载gif图的第一帧。
ok，接下来看Glide的图片缓存：
设置磁盘缓存
Glide.with(this).load(url).diskCacheStrategy(DiskCacheStrategy.ALL).into(imageView);
对应的缓存参数如下：
缓存参数说明
DiskCacheStrategy.NONE：不缓存任何图片，即禁用磁盘缓存
DiskCacheStrategy.ALL ：缓存原始图片 & 转换后的图片（默认）
DiskCacheStrategy.SOURCE：只缓存原始图片（原来的全分辨率的图像，即不缓存转换后的图片）
DiskCacheStrategy.RESULT：只缓存转换后的图片（即最终的图像：降低分辨率后 / 或者转换后 ，不缓存原始图片
ok，基本用法讲解完毕，之后就从用法出发，开始分析Glide的源码。
先来看with()方法，with方法传了一个Context进去，其实很简单，就是绑定Glide生命周期的意思，来看源码：
public static RequestManager with(Context context) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(context);
}
public static RequestManager with(Activity activity) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(activity);
}
public static RequestManager with(FragmentActivity activity) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(activity);
}
with()方法有很多重构方法，其实也就是参数不同而已，实现里可以看到都是跟RequestManagerRetriever这个类有关，RequestManagerRetriever.get()方法从代码里可以看到是为了得到它的单例，那就来看看RequestManagerRetriever这个类，先看下面这三个我抽取出来的方法：
public RequestManager get(Context context) {
if (context == null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
} else if (Util.isOnMainThread() && !(context instanceof Application)) {
if (context instanceof FragmentActivity) {
return get((FragmentActivity) context);
} else if (context instanceof Activity) {
return get((Activity) context);
} else if (context instanceof ContextWrapper) {
return get(((ContextWrapper) context).getBaseContext());
}
}
return getApplicationManager(context);
}
public RequestManager get(FragmentActivity activity) {
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
FragmentManager fm = activity.getSupportFragmentManager();
return supportFragmentGet(activity, fm);
}
}
private RequestManager getApplicationManager(Context context) {
if (applicationManager == null) {
synchronized (this) {
if (applicationManager == null) {
applicationManager = new RequestManager(context.getApplicationContext(),
new ApplicationLifecycle(), new EmptyRequestManagerTreeNode());
}
}
}
return applicationManager;
}
第一个方法中context传进来以后把FragmentActivity，Activity，ContextWrapper都分流出去，除了这三种情况之外（其实也就是application context）都return getApplicationManager(context)也就是上面代码中的第三个方法。从上述代码可以看出，当传入的context是application或者在子线程中，那么最后都会调用getApplicationManager，在getApplicationManager(Context context)方法中，创建了一个RequestManager对象，因为Application的生命周期是跟着app的生命周期的，所以当传入的context为application的时候Glide没有进行任何关于生命周期的判断。先来看另外一种也就是当传入Activity这些的时候：
RequestManager supportFragmentGet(Context context, FragmentManager fm) {
SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
current.setRequestManager(requestManager);
}
return requestManager;
}
@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;
}
RequestManager supportFragmentGet(Context context, FragmentManager fm) {
SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
current.setRequestManager(requestManager);
}
return requestManager;
}
我们发现到最后也是创建了一个RequestManager对象，从后面两个方法可以看出，不管你context传入的是Activity还是FragmentActivitiy，都会在Activity的基础上创建一个Fragment，这是为什么呢？因为Glide无法监听到Activity的生命周期，所以往Activity中添加一个Fragment来监听Fragment的生命周期，因为如果Activity消亡了，Fragment当然也就消亡了，具体代码看下面，不过传入的参数跟之前Application的不同，这里的SupportRequestManagerFragment的current.getLifecycle()方法我们进去会发现这其实是一个继承了Fragment的类，也就是往Activity里添加的Fragment，lifecycle实现了各种生命周期的方法：
@Override
public void onStart() {
super.onStart();
lifecycle.onStart();
}
@Override
public void onStop() {
super.onStop();
lifecycle.onStop();
}
@Override
public void onDestroy() {
super.onDestroy();
lifecycle.onDestroy();
}
ok那现在回到RequestManager这个类，实现了LifecycleListener接口：
public interface LifecycleListener {
/**
* Callback for when {@link android.app.Fragment#onStart()}} or {@link android.app.Activity#onStart()} is called.
*/
void onStart();
/**
* Callback for when {@link android.app.Fragment#onStop()}} or {@link android.app.Activity#onStop()}} is called.
*/
void onStop();
/**
* Callback for when {@link android.app.Fragment#onDestroy()}} or {@link android.app.Activity#onDestroy()} is
* called.
*/
void onDestroy();
}
在RequestManager类中分别在这三个生命周期方法中实现了各自的操作，操作代码全都在RequestTracker这个类里，这个类主要负责跟踪，取消，重启在进程中的或者已经完成了或者已经失败了的请求，看RequestTracker可知其实就是在Glide内部维护了一个Request请求的list：
public class RequestTracker {
private final Set<Request> requests = Collections.newSetFromMap(new WeakHashMap<Request, Boolean>());
@SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
private final List<Request> pendingRequests = new ArrayList<Request>();
private boolean isPaused;
public void runRequest(Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
void addRequest(Request request) {
requests.add(request);
}
public void removeRequest(Request request) {
requests.remove(request);
pendingRequests.remove(request);
}
public boolean isPaused() {
return isPaused;
}
public void pauseRequests() {
isPaused = true;
for (Request request : Util.getSnapshot(requests)) {
if (request.isRunning()) {
request.pause();
pendingRequests.add(request);
}
}
}
public void resumeRequests() {
isPaused = false;
for (Request request : Util.getSnapshot(requests)) {
if (!request.isComplete() && !request.isCancelled() && !request.isRunning()) {
request.begin();
}
}
pendingRequests.clear();
}
public void clearRequests() {
for (Request request : Util.getSnapshot(requests)) {
request.clear();
}
pendingRequests.clear();
}
public void restartRequests() {
for (Request request : Util.getSnapshot(requests)) {
if (!request.isComplete() && !request.isCancelled()) {
// Ensure the request will be restarted in onResume.
request.pause();
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
}
}
}
其实给Glide添加生命周期的意义很简单，当你在一个Activity里去加载图片，当图片还没加载出来的时候用户把Activity消亡了，那图片加载的request是不是得取消，其实就是这么一个道理。
ok，接下来来看load()方法，因为with(context)方法返回的是RequestManager，所以load()方法自然也就在RequestManager类里，可以看到：
public DrawableTypeRequest<String> load(String string) {
return (DrawableTypeRequest<String>) fromString().load(string);
}
方法实现非常简单，先来看fromString()，点到fromString()方法发现其实就是调用了loadGeneric(String.class)方法，ok那就来看loadGeneric()方法：
private <T> DrawableTypeRequest<T> loadGeneric(Class<T> modelClass) {
ModelLoader<T, InputStream> streamModelLoader = Glide.buildStreamModelLoader(modelClass, context);
ModelLoader<T, ParcelFileDescriptor> fileDescriptorModelLoader =
Glide.buildFileDescriptorModelLoader(modelClass, context);
if (modelClass != null && streamModelLoader == null && fileDescriptorModelLoader == null) {
throw new IllegalArgumentException("Unknown type " + modelClass + ". You must provide a Model of a type for"
+ " which there is a registered ModelLoader, if you are using a custom model, you must first call"
+ " Glide#register with a ModelLoaderFactory for your custom model class");
}
return optionsApplier.apply(
new DrawableTypeRequest<T>(modelClass, streamModelLoader, fileDescriptorModelLoader, context,
glide, requestTracker, lifecycle, optionsApplier));
}
在这个方法里其实就是根据传进来的class类来创建不同的ModelLoader类，然后再把这些参数都穿进去创造一个DrawableTypeRequest对象返回回去，因为这里我参考的是load(url)加载网络图片链接，所以传进去的就是String，这个ModelLoader是干嘛的呢，接着往下看，Glide.buildStreamModelLoader(modelClass, context):
/**
* A method to build a {@link ModelLoader} for the given model that produces {@link InputStream}s using a registered
* factory.
*
* @see #buildModelLoader(Class, Class, android.content.Context)
*/
public static <T> ModelLoader<T, InputStream> buildStreamModelLoader(Class<T> modelClass, Context context) {
return buildModelLoader(modelClass, InputStream.class, context);
}
//省略一大段代码
public static <T, Y> ModelLoader<T, Y> buildModelLoader(Class<T> modelClass, Class<Y> resourceClass,
Context context) {
if (modelClass == null) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Unable to load null model, setting placeholder only");
}
return null;
}
return Glide.get(context).getLoaderFactory().buildModelLoader(modelClass, resourceClass);
}
创建一个ModelLoader对象有什么用呢？其实就是为了提供inputStream输入流，可以看到该方法最后return了一个buildModelLoader(modelClass, resourceClass)的对象，接下来就进入到这个方法，这个方法在GenericLoaderFactory类里面，GenericLoaderFactory这个类其实比较短，所以全部简略的全部贴出来：
public class GenericLoaderFactory {
private final Map<Class/*T*/, Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/>> modelClassToResourceFactories =
new HashMap<Class, Map<Class, ModelLoaderFactory>>();
private final Map<Class/*T*/, Map<Class/*Y*/, ModelLoader/*T, Y*/>> cachedModelLoaders =
new HashMap<Class, Map<Class, ModelLoader>>();
private static final ModelLoader NULL_MODEL_LOADER = new ModelLoader() {
@Override
public DataFetcher getResourceFetcher(Object model, int width, int height) {
throw new NoSuchMethodError("This should never be called!");
}
@Override
public String toString() {
return "NULL_MODEL_LOADER";
}
};
private final Context context;
public GenericLoaderFactory(Context context) {
this.context = context.getApplicationContext();
}
public synchronized <T, Y> ModelLoaderFactory<T, Y> unregister(Class<T> modelClass, Class<Y> resourceClass) {
cachedModelLoaders.clear();
ModelLoaderFactory/*T, Y*/ result = null;
Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> resourceToFactories = modelClassToResourceFactories.get(modelClass);
if (resourceToFactories != null) {
result = resourceToFactories.remove(resourceClass);
}
return result;
}
public synchronized <T, Y> ModelLoaderFactory<T, Y> register(Class<T> modelClass, Class<Y> resourceClass,
ModelLoaderFactory<T, Y> factory) {
cachedModelLoaders.clear();
Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> resourceToFactories = modelClassToResourceFactories.get(modelClass);
if (resourceToFactories == null) {
resourceToFactories = new HashMap<Class/*Y*/, ModelLoaderFactory/*T, Y*/>();
modelClassToResourceFactories.put(modelClass, resourceToFactories);
}
ModelLoaderFactory/*T, Y*/ previous = resourceToFactories.put(resourceClass, factory);
if (previous != null) {
// This factory may be being used by another model. We don't want to say it has been removed unless we
// know it has been removed for all models.
for (Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> factories : modelClassToResourceFactories.values()) {
if (factories.containsValue(previous)) {
previous = null;
break;
}
}
}
return previous;
}
@Deprecated
public synchronized <T, Y> ModelLoader<T, Y> buildModelLoader(Class<T> modelClass, Class<Y> resourceClass,
Context context) {
return buildModelLoader(modelClass, resourceClass);
}
public synchronized <T, Y> ModelLoader<T, Y> buildModelLoader(Class<T> modelClass, Class<Y> resourceClass) {
ModelLoader<T, Y> result = getCachedLoader(modelClass, resourceClass);
if (result != null) {
// We've already tried to create a model loader and can't with the currently registered set of factories,
// but we can't use null to demonstrate that failure because model loaders that haven't been requested
// yet will be null in the cache. To avoid this, we use a special signal model loader.
if (NULL_MODEL_LOADER.equals(result)) {
return null;
} else {
return result;
}
}
final ModelLoaderFactory<T, Y> factory = getFactory(modelClass, resourceClass);
if (factory != null) {
result = factory.build(context, this);
cacheModelLoader(modelClass, resourceClass, result);
} else {
// We can't generate a model loader for the given arguments with the currently registered set of factories.
cacheNullLoader(modelClass, resourceClass);
}
return result;
}
private <T, Y> void cacheNullLoader(Class<T> modelClass, Class<Y> resourceClass) {
cacheModelLoader(modelClass, resourceClass, NULL_MODEL_LOADER);
}
private <T, Y> void cacheModelLoader(Class<T> modelClass, Class<Y> resourceClass, ModelLoader<T, Y> modelLoader) {
Map<Class/*Y*/, ModelLoader/*T, Y*/> resourceToLoaders = cachedModelLoaders.get(modelClass);
if (resourceToLoaders == null) {
resourceToLoaders = new HashMap<Class/*Y*/, ModelLoader/*T, Y*/>();
cachedModelLoaders.put(modelClass, resourceToLoaders);
}
resourceToLoaders.put(resourceClass, modelLoader);
}
private <T, Y> ModelLoader<T, Y> getCachedLoader(Class<T> modelClass, Class<Y> resourceClass) {
Map<Class/*Y*/, ModelLoader/*T, Y*/> resourceToLoaders = cachedModelLoaders.get(modelClass);
ModelLoader/*T, Y*/ result = null;
if (resourceToLoaders != null) {
result = resourceToLoaders.get(resourceClass);
}
return result;
}
private <T, Y> ModelLoaderFactory<T, Y> getFactory(Class<T> modelClass, Class<Y> resourceClass) {
Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> resourceToFactories = modelClassToResourceFactories.get(modelClass);
ModelLoaderFactory/*T, Y*/ result = null;
if (resourceToFactories != null) {
result = resourceToFactories.get(resourceClass);
}
if (result == null) {
for (Class<? super T> registeredModelClass : modelClassToResourceFactories.keySet()) {
if (registeredModelClass.isAssignableFrom(modelClass)) {
Map<Class/*Y*/, ModelLoaderFactory/*T, Y*/> currentResourceToFactories =
modelClassToResourceFactories.get(registeredModelClass);
if (currentResourceToFactories != null) {
result = currentResourceToFactories.get(resourceClass);
if (result != null) {
break;
}
}
}
}
}
return result;
}
}
重点来看buildModelLoader方法，这里的T跟Y范型类在我的心路历程里其实就是String跟InputStream。我们可以看到其实我们是通过getFactory(modelClass, resourceClass)这个方法来创建了一个ModelLoaderFactory对象的，看getFactory方法可以看到我们其实就是从一个modelClassToResourceFactories的map获取一个ModelLoaderFactory对象，而且是要已经注册过了的，至于怎么判断是否注册过，就要回到Glide的构造方法：
Glide(Engine engine, MemoryCache memoryCache, BitmapPool bitmapPool, Context context, DecodeFormat decodeFormat) {
this.engine = engine;
this.bitmapPool = bitmapPool;
this.memoryCache = memoryCache;
this.decodeFormat = decodeFormat;
loaderFactory = new GenericLoaderFactory(context);
mainHandler = new Handler(Looper.getMainLooper());
bitmapPreFiller = new BitmapPreFiller(memoryCache, bitmapPool, decodeFormat);
dataLoadProviderRegistry = new DataLoadProviderRegistry();
StreamBitmapDataLoadProvider streamBitmapLoadProvider =
new StreamBitmapDataLoadProvider(bitmapPool, decodeFormat);
dataLoadProviderRegistry.register(InputStream.class, Bitmap.class, streamBitmapLoadProvider);
FileDescriptorBitmapDataLoadProvider fileDescriptorLoadProvider =
new FileDescriptorBitmapDataLoadProvider(bitmapPool, decodeFormat);
dataLoadProviderRegistry.register(ParcelFileDescriptor.class, Bitmap.class, fileDescriptorLoadProvider);
ImageVideoDataLoadProvider imageVideoDataLoadProvider =
new ImageVideoDataLoadProvider(streamBitmapLoadProvider, fileDescriptorLoadProvider);
dataLoadProviderRegistry.register(ImageVideoWrapper.class, Bitmap.class, imageVideoDataLoadProvider);
GifDrawableLoadProvider gifDrawableLoadProvider =
new GifDrawableLoadProvider(context, bitmapPool);
dataLoadProviderRegistry.register(InputStream.class, GifDrawable.class, gifDrawableLoadProvider);
dataLoadProviderRegistry.register(ImageVideoWrapper.class, GifBitmapWrapper.class,
new ImageVideoGifDrawableLoadProvider(imageVideoDataLoadProvider, gifDrawableLoadProvider, bitmapPool));
dataLoadProviderRegistry.register(InputStream.class, File.class, new StreamFileDataLoadProvider());
register(File.class, ParcelFileDescriptor.class, new FileDescriptorFileLoader.Factory());
register(File.class, InputStream.class, new StreamFileLoader.Factory());
register(int.class, ParcelFileDescriptor.class, new FileDescriptorResourceLoader.Factory());
register(int.class, InputStream.class, new StreamResourceLoader.Factory());
register(Integer.class, ParcelFileDescriptor.class, new FileDescriptorResourceLoader.Factory());
register(Integer.class, InputStream.class, new StreamResourceLoader.Factory());
register(String.class, ParcelFileDescriptor.class, new FileDescriptorStringLoader.Factory());
register(String.class, InputStream.class, new StreamStringLoader.Factory());
register(Uri.class, ParcelFileDescriptor.class, new FileDescriptorUriLoader.Factory());
register(Uri.class, InputStream.class, new StreamUriLoader.Factory());
register(URL.class, InputStream.class, new StreamUrlLoader.Factory());
register(GlideUrl.class, InputStream.class, new HttpUrlGlideUrlLoader.Factory());
register(byte[].class, InputStream.class, new StreamByteArrayLoader.Factory());
transcoderRegistry.register(Bitmap.class, GlideBitmapDrawable.class,
new GlideBitmapDrawableTranscoder(context.getResources(), bitmapPool));
transcoderRegistry.register(GifBitmapWrapper.class, GlideDrawable.class,
new GifBitmapWrapperDrawableTranscoder(
new GlideBitmapDrawableTranscoder(context.getResources(), bitmapPool)));
bitmapCenterCrop = new CenterCrop(bitmapPool);
drawableCenterCrop = new GifBitmapWrapperTransformation(bitmapPool, bitmapCenterCrop);
bitmapFitCenter = new FitCenter(bitmapPool);
drawableFitCenter = new GifBitmapWrapperTransformation(bitmapPool, bitmapFitCenter);
}
这里注册了FileDescriptorFileLoader、StreamFileLoader等好几个factory，因为我们这里传入的是String跟InputStream所以我们得到的factory其实是StreamStringLoader，后面的那个fileDescriptorModeLoader方法跟这里类似，所以这里就不详述了。
ok，到这里我们就回去，经过这么一串分析之后就生成了一个DrawableTypeRequest对象，那么DrawableTypeRequest究竟是什么呢。。接下来就来look下这个，代码比较少：
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));
}
/**
* {@inheritDoc}
*/
public <Y extends Target<File>> Y downloadOnly(Y target) {
return getDownloadOnlyRequest().downloadOnly(target);
}
/**
* {@inheritDoc}
*/
public FutureTarget<File> downloadOnly(int width, int height) {
return getDownloadOnlyRequest().downloadOnly(width, height);
}
private GenericTranscodeRequest<ModelType, InputStream, File> getDownloadOnlyRequest() {
return optionsApplier.apply(new GenericTranscodeRequest<ModelType, InputStream, File>(File.class, this,
streamModelLoader, InputStream.class, File.class, optionsApplier));
}
}
眼神好的朋友们是不是已经发现了asBitmap()跟asGif()两个我们之前说用法上的方法了。经过了一层一层底层方法的穿来穿去之后，突然发现这两个方法是不是很舒服。其实很简单，就是分别创建了一个BitmapTypeRequest和GifTypeRequest，根据不同的request然后底层再去加载不同的图片格式。
ok，接下去我们再回到开头，fromString()方法之后返回一个DrawableTypeRequest对象，然后就是调用这个对象的load(string)方法，我们看到load方法其实是跳到了父类DrawableRequestBuilder里，那就来看看它的父类：
//省略一部分代码
public DrawableRequestBuilder<ModelType> centerCrop() {
return transform(glide.getDrawableCenterCrop());
}
@SuppressWarnings("unchecked")
public DrawableRequestBuilder<ModelType> fitCenter() {
return transform(glide.getDrawableFitCenter());
}
public DrawableRequestBuilder<ModelType> bitmapTransform(Transformation<Bitmap>... bitmapTransformations) {
GifBitmapWrapperTransformation[] transformations =
new GifBitmapWrapperTransformation[bitmapTransformations.length];
for (int i = 0; i < bitmapTransformations.length; i++) {
transformations[i] = new GifBitmapWrapperTransformation(glide.getBitmapPool(), bitmapTransformations[i]);
}
return transform(transformations);
}
/**
* {@inheritDoc}
*
* @see #bitmapTransform(com.bumptech.glide.load.Transformation[])
* @see #centerCrop()
* @see #fitCenter()
*/
@Override
public DrawableRequestBuilder<ModelType> transform(Transformation<GifBitmapWrapper>... transformation) {
super.transform(transformation);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> transcoder(
ResourceTranscoder<GifBitmapWrapper, GlideDrawable> transcoder) {
super.transcoder(transcoder);
return this;
}
/**
* {@inheritDoc}
*/
public final DrawableRequestBuilder<ModelType> crossFade() {
super.animate(new DrawableCrossFadeFactory<GlideDrawable>());
return this;
}
/**
* {@inheritDoc}
*/
public DrawableRequestBuilder<ModelType> crossFade(int duration) {
super.animate(new DrawableCrossFadeFactory<GlideDrawable>(duration));
return this;
}
/**
* {@inheritDoc}
*/
@Deprecated
public DrawableRequestBuilder<ModelType> crossFade(Animation animation, int duration) {
super.animate(new DrawableCrossFadeFactory<GlideDrawable>(animation, duration));
return this;
}
/**
* {@inheritDoc}
*/
public DrawableRequestBuilder<ModelType> crossFade(int animationId, int duration) {
super.animate(new DrawableCrossFadeFactory<GlideDrawable>(context, animationId,
duration));
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> dontAnimate() {
super.dontAnimate();
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> animate(ViewPropertyAnimation.Animator animator) {
super.animate(animator);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> animate(int animationId) {
super.animate(animationId);
return this;
}
/**
* {@inheritDoc}
*/
@Deprecated
@SuppressWarnings("deprecation")
@Override
public DrawableRequestBuilder<ModelType> animate(Animation animation) {
super.animate(animation);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> placeholder(int resourceId) {
super.placeholder(resourceId);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> placeholder(Drawable drawable) {
super.placeholder(drawable);
return this;
}
@Override
public DrawableRequestBuilder<ModelType> fallback(Drawable drawable) {
super.fallback(drawable);
return this;
}
@Override
public DrawableRequestBuilder<ModelType> fallback(int resourceId) {
super.fallback(resourceId);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> error(int resourceId) {
super.error(resourceId);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> error(Drawable drawable) {
super.error(drawable);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> listener(
RequestListener<? super ModelType, GlideDrawable> requestListener) {
super.listener(requestListener);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> diskCacheStrategy(DiskCacheStrategy strategy) {
super.diskCacheStrategy(strategy);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> skipMemoryCache(boolean skip) {
super.skipMemoryCache(skip);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> override(int width, int height) {
super.override(width, height);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> sourceEncoder(Encoder<ImageVideoWrapper> sourceEncoder) {
super.sourceEncoder(sourceEncoder);
return this;
}
/**
* {@inheritDoc}
*/
@Override
public DrawableRequestBuilder<ModelType> dontTransform() {
super.dontTransform();
return this;
}
@Override
public DrawableRequestBuilder<ModelType> signature(Key signature) {
super.signature(signature);
return this;
}
@Override
public DrawableRequestBuilder<ModelType> load(ModelType model) {
super.load(model);
return this;
}
@Override
public DrawableRequestBuilder<ModelType> clone() {
return (DrawableRequestBuilder<ModelType>) super.clone();
}
@Override
public Target<GlideDrawable> into(ImageView view) {
return super.into(view);
}
@Override
void applyFitCenter() {
fitCenter();
}
@Override
void applyCenterCrop() {
centerCrop();
}
有没有觉得很亲切，之前用法里我们用到的很多api方法我们终于看到了，当然我们也看到了into()方法，load方法我们先来看看它父类的实现：
public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> load(ModelType model) {
this.model = model;
isModelSet = true;
return this;
}
其实就是做了一个状态的保存而已。
ok，那接下来我们就开始分析into()方法，into()方法我逻辑理了n遍，实在太复杂了我的天，稍微注意力不集中一下就晕了。。ok，废话不多说，接着来，into()。
首先，我们定位到DrawableTypeRequest的父类GenericRequestBuilder里的into()方法：
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));
}
前面一大堆讲的都是图片变化的问题，暂时先放到一边，先来看图片加载的过程，也就是最后一句话，先来看buildImageViewTarget(view, transcoderClass)方法：
<R> Target<R> buildImageViewTarget(ImageView imageView, Class<R> transcodedClass) {
return imageViewTargetFactory.buildTarget(imageView, transcodedClass);
}
之前的分析中可以看出transcodedClass也就是TranscodeType的一个实体类，而TranscodeType也就是GlideDrawable类，知道了这个以后那就接着往下看：
public class ImageViewTargetFactory {
@SuppressWarnings("unchecked")
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)");
}
}
}
这里我们看到了三个类GlideDrawableImageViewTarget、BitmapImageViewTarget、DrawableImageViewTarget。在这里，我们也就创建了一个GlideDrawableImageViewTarget对象了。ok，我们知道了这个以后现在回过头去看之前的into(Y target)方法：
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;
}
ok，到这里我们终于发现发出加载图片请求的类了，也就是Request，Request类的具体子类的作用就是根据图片路径来加载图片到imageView上。这里Request对象是通过buildRequest(target)方法来创建的，ok，接下来看这个：
private Request buildRequest(Target<TranscodeType> target) {
if (priority == null) {
priority = Priority.NORMAL;
}
return buildRequestRecursive(target, null);
}
private Request buildRequestRecursive(Target<TranscodeType> target, ThumbnailRequestCoordinator parentCoordinator) {
if (thumbnailRequestBuilder != null) {
if (isThumbnailBuilt) {
throw new IllegalStateException("You cannot use a request as both the main request and a thumbnail, "
+ "consider using clone() on the request(s) passed to thumbnail()");
}
// Recursive case: contains a potentially recursive thumbnail request builder.
if (thumbnailRequestBuilder.animationFactory.equals(NoAnimation.getFactory())) {
thumbnailRequestBuilder.animationFactory = animationFactory;
}
if (thumbnailRequestBuilder.priority == null) {
thumbnailRequestBuilder.priority = getThumbnailPriority();
}
if (Util.isValidDimensions(overrideWidth, overrideHeight)
&& !Util.isValidDimensions(thumbnailRequestBuilder.overrideWidth,
thumbnailRequestBuilder.overrideHeight)) {
thumbnailRequestBuilder.override(overrideWidth, overrideHeight);
}
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest = obtainRequest(target, sizeMultiplier, priority, coordinator);
// Guard against infinite recursion.
isThumbnailBuilt = true;
// Recursively generate thumbnail requests.
Request thumbRequest = thumbnailRequestBuilder.buildRequestRecursive(target, coordinator);
isThumbnailBuilt = false;
coordinator.setRequests(fullRequest, thumbRequest);
return coordinator;
} else if (thumbSizeMultiplier != null) {
// Base case: thumbnail multiplier generates a thumbnail request, but cannot recurse.
ThumbnailRequestCoordinator coordinator = new ThumbnailRequestCoordinator(parentCoordinator);
Request fullRequest = obtainRequest(target, sizeMultiplier, priority, coordinator);
Request thumbnailRequest = obtainRequest(target, thumbSizeMultiplier, getThumbnailPriority(), coordinator);
coordinator.setRequests(fullRequest, thumbnailRequest);
return coordinator;
} else {
// Base case: no thumbnail.
return obtainRequest(target, sizeMultiplier, priority, parentCoordinator);
}
}
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);
}
buildRequest方法里调用了buildRequestRecursive方法，这个里面代码不少，我们先把图片变化的都忽略，就会发现主要的还是botainRequest()方法，然后看到return了一个GenericRequest.obtain(n个参数)的方法，这么多参数，乍看一下你会觉得很熟悉，placehoderId，errorId等，这些不都是我们最开始讲Glide的时候用的一些api方法莫，是不是有一种胜利在望的感觉。。ok，那就接着往下看obtain()方法，进入了GenericRequest类：
public static <A, T, Z, R> GenericRequest<A, T, Z, R> obtain(
LoadProvider<A, T, Z, R> loadProvider,
A model,
Key signature,
Context context,
Priority priority,
Target<R> target,
float sizeMultiplier,
Drawable placeholderDrawable,
int placeholderResourceId,
Drawable errorDrawable,
int errorResourceId,
Drawable fallbackDrawable,
int fallbackResourceId,
RequestListener<? super A, R> requestListener,
RequestCoordinator requestCoordinator,
Engine engine,
Transformation<Z> transformation,
Class<R> transcodeClass,
boolean isMemoryCacheable,
GlideAnimationFactory<R> animationFactory,
int overrideWidth,
int overrideHeight,
DiskCacheStrategy diskCacheStrategy) {
@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;
}
乍看一下头已经晕了。。。放松一下，仔细看，我们发现传进来这么多参数以后，方法里先去创建了一个GenericRequest的实体类，然后调用了init方法，进去看，会发现全是一个赋值的一个过程，ok，既然是这样子，我们已经知道了request创建的整个过程了莫，这条路就差不多走到底了，差不多该回去了，那就再回到into方法。
Request request = buildRequest(target);
target.setRequest(request);
lifecycle.addListener(target);
requestTracker.runRequest(request);
首先先把request绑定给了GlideDrawableImageViewTarget对象，为了就是不会被Glide之外的调用，然后我们看到，runRequest(request)方法，直觉告诉我们request对象创建出来之后执行代码应该就在这里了，那我们就进去看看，果然。。
public void runRequest(Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
这个方法在RequestTracker类里，这个类是不是很熟悉，之前在讲with()方法的生命周期里提到过。这个方法里做了一个很简单的逻辑判断，如果这个时候不是暂停状态的话，request.begin()方法去执行request，否则就把该request存放到一个放着没有完成或者可能会重新去运行一遍的request的list里面。接着一步一步下去，进begin()方法。因为之前我们request的创建过程中一步一步下来到最后是return了一个GenericRequest.obtain(n个参数)，所以begin()方法就应该在GenericRequest类里面，ok，定位到begin()方法：
@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));
}
}
ok，这个beging()方法我们慢慢来分析，首先我们先来看model是什么？我们往前看，翻到GenericRequestBuilder的构造函数，然后创建它对象的过程发现model其实在我们这种情况下就是图片的链接地址，也就是load里传过来的东西，因为这里我们分析的是加载网络请求图片，所以也就是图片的链接。ok，知道了model是什么以后我们再来看这个方法，如果model是空的，那么就调用onException(null)方法，我们来看这个方法
@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);
}
}
哦？这里有个备注：如果这里是缩略图请求怎么办？我思考了半天也是不解这里为什么会有个问号备注，当然这不是重点。这里把图片加载的状态设置了failed，然后调用了setErrorPlacehoder(e)方法，看方法名字就知道这是在设置错误缺省图。
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);
}
这里我们发现还有一个canNotifyStatusChanged这么一个变量，有一个监听状态是否改变的过程确保了安全性和正确性。再来看这两个方法获取了placeholder跟error的图片：
private Drawable getErrorDrawable() {
if (errorDrawable == null && errorResourceId > 0) {
errorDrawable = context.getResources().getDrawable(errorResourceId);
}
return errorDrawable;
}
private Drawable getPlaceholderDrawable() {
if (placeholderDrawable == null && placeholderResourceId > 0) {
placeholderDrawable = context.getResources().getDrawable(placeholderResourceId);
}
return placeholderDrawable;
}
接下来来看target.onLoadFailed(e, error)这个方法，要找这个方法又得回到最初的地方，因为target其实也就是GenericRequestBuilder里的into方法里glide.buildImageView()，所以onLoadFailed方法也就应该在ImageViewTarget类里面。
@Override
public void onLoadFailed(Exception e, Drawable errorDrawable) {
view.setImageDrawable(errorDrawable);
}
很easy，给view设置图片，当然这里我们还看到了设置缺省图:
@Override
public void onLoadStarted(Drawable placeholder) {
view.setImageDrawable(placeholder);
}
ok，看完错误缺省图的加载过程之后我们再回到GenericRequest类的begin()方法，看源码就是一个走迷宫的过程，一条路走到底了，然后再回头继续走下一条路，注意力稍微有一点不集中，就懵了。。。来看if跟else，if(Util.isValidDimensions(overrideWidth, overrideHeight))看了下工具类里这个方法，也就是说如果宽度和高度都是指定的话，也就是固定的话，就调用onSizeReady(width, height)方法，不然的话就调用target.getSize(this)方法，ok，我们先来看getSize()方法，跟之前的onLoadFailed一样，target就是ImageViewTarget，但是在里面找不到getSize()方法，所以应该在他的父类里，也就是ViewTarget类里找到了这个方法：
@Override
public void getSize(SizeReadyCallback cb) {
sizeDeterminer.getSize(cb);
}
private static class SizeDeterminer {
private void notifyCbs(int width, int height) {
for (SizeReadyCallback cb : cbs) {
cb.onSizeReady(width, height);
}
cbs.clear();
}
//省略代码。。。。。。
public void getSize(SizeReadyCallback cb) {
int currentWidth = getViewWidthOrParam();
int currentHeight = getViewHeightOrParam();
if (isSizeValid(currentWidth) && isSizeValid(currentHeight)) {
cb.onSizeReady(currentWidth, currentHeight);
} else {
// We want to notify callbacks in the order they were added and we only expect one or two callbacks to
// be added a time, so a List is a reasonable choice.
if (!cbs.contains(cb)) {
cbs.add(cb);
}
if (layoutListener == null) {
final ViewTreeObserver observer = view.getViewTreeObserver();
layoutListener = new SizeDeterminerLayoutListener(this);
observer.addOnPreDrawListener(layoutListener);
}
}
}
//省略一大段代码
}
}
我们可以看到，这里其实根据imageView的width，height做了一系列的计算之后得出了图片应该显示的多宽跟多高。计算结束之后，我们可以看到在SizeDeterminer里面最后的最后还是调用了onSizeReady()方法。那我们就来看看这个方法里到底干了什么：
@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));
}
}
ok我们在这里又看到了ModelLoader，是不是很惊喜是不是很惊讶，这里通过loadProvider创建了一个ModelLoader，这个loadProvider又是什么东西呢？这我们就得回去回去看了。让我们回到load()方法，还记得我们load()方法里在buildModelLoader()的时候通过getFactory()创建了一个ModelLoaderFactory嘛，我们在那里生成返回了一个DrawableTypeRequest对象，在创建DrawableTypeRequest的时候new出了一个FixedLoadProvider类，而这个loadProvider其实就是FixedLoadProvider类的一个封装类ChildLoadProvider的一个实体对象。我们可以看看GenericRequestBuilder类的构造函数：
GenericRequestBuilder(Context context, Class<ModelType> modelClass,
LoadProvider<ModelType, DataType, ResourceType, TranscodeType> loadProvider,
Class<TranscodeType> transcodeClass, Glide glide, RequestTracker requestTracker, Lifecycle lifecycle) {
this.context = context;
this.modelClass = modelClass;
this.transcodeClass = transcodeClass;
this.glide = glide;
this.requestTracker = requestTracker;
this.lifecycle = lifecycle;
this.loadProvider = loadProvider != null
? new ChildLoadProvider<ModelType, DataType, ResourceType, TranscodeType>(loadProvider) : null;
if (context == null) {
throw new NullPointerException("Context can't be null");
}
if (modelClass != null && loadProvider == null) {
throw new NullPointerException("LoadProvider must not be null");
}
}
ok，之后我们再回到onSizeReady()方法，之后调用了modelLoader.getResourceFetcher(model, width, height)方法，这个又是干嘛的呢？进去看看，getResourceFetcher()方法在哪里呢。。我们看到之前DrawableTypeRequest的构造函数里其实把loadGeneric()方法中创建的两个modelLoader对象都封装到了ImageVideoModelLoader这个类里面并new出了一个对象，所以getResourceFetcher()应该在这个里面：
verride
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;
}
}
因为我们现在是第一次调用Glide加载图片，所以生成一个HttpUrlFetch对象。这里绕来绕去其实最后getResourceFetch()方法最后还是返回一个ImageVideoFetcher对象。然后我们再回去onSizeReady()方法，然后就是把这些new出来的东西全部传到engine.load()方法里面去。也就是这句话：
loadStatus = engine.load(signature, width, height, dataFetcher, loadProvider, transformation, transcoder,
priority, isMemoryCacheable, diskCacheStrategy, this);
那接下去就来看看Engine呗，Engine这个类看注释主要是负责加载以及管理活跃的和已经缓存了的资源。我们先暂时不看缓存相关的东西，等会讲缓存的东西的时候再翻回来看，我们现在先看加载的整个流程。ok，那我们来看Engine这个类里的load方法：
public <T, Z, R> LoadStatus load(Key signature, int width, int height, DataFetcher<T> fetcher,
DataLoadProvider<T, Z> loadProvider, Transformation<Z> transformation, ResourceTranscoder<Z, R> transcoder,
Priority priority, boolean isMemoryCacheable, DiskCacheStrategy diskCacheStrategy, ResourceCallback cb) {
Util.assertMainThread();
long startTime = LogTime.getLogTime();
final String id = fetcher.getId();
EngineKey key = keyFactory.buildKey(id, signature, width, height, loadProvider.getCacheDecoder(),
loadProvider.getSourceDecoder(), transformation, loadProvider.getEncoder(),
transcoder, loadProvider.getSourceEncoder());
EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
if (cached != null) {
cb.onResourceReady(cached);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Loaded resource from cache", startTime, key);
}
return null;
}
EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
if (active != null) {
cb.onResourceReady(active);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Loaded resource from active resources", startTime, key);
}
return null;
}
EngineJob current = jobs.get(key);
if (current != null) {
current.addCallback(cb);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
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);
}
忽略缓存相关的代码，首先创建了个EngineJob对象，然后创建了一个DecodeJob对象，然后把这两个对象穿进去创建了EngineRunnable对象，之后start()，ok所以我们现在就来重点看一下 EngineRunnable的run()方法。
@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);
}
}
后面我们可以看到一个是请求取消了的情况，一个是加载失败了，一个是加载完成了，所以基本上记载的过程应该都是在decode()这个方法里面，进去：
private Resource<?> decode() throws Exception {
if (isDecodingFromCache()) {
return decodeFromCache();
} else {
return decodeFromSource();
}
}
顾名思义，一个是从缓存里获取图片，不然就去执行decodeFromSource()方法，ok，我们这里先走流程，先看decodeFromSouce()方法：
private Resource<?> decodeFromSource() throws Exception {
return decodeJob.decodeFromSource();
}
再进入到decodeFromSource()方法进入到DecodeJob类里：
public Resource<Z> decodeFromSource() throws Exception {
Resource<T> decoded = decodeSource();
return transformEncodeAndTranscode(decoded);
}
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;
}
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;
}
因为简书文章限度问题，接下来的就只能分篇写了。。。
下文链接：http://www.jianshu.com/p/8104be187f10
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