Glide源码解读(一)
#Glide 流程 3.5.2
作为一个优秀的通用图片加载库。有着几乎所有的优点，使用简单,加载各种格式图片资源，预加载图片资源，根据控件大小合理缩放资源，支持图像变换操作等等，既然这么优秀的框架，那就值得我们好好深入理解它的设计和实现原理。现在我们跟随源码一探究竟
with方法有很多重载方法
1 使用，一行代码搞定
Glide.with(context).load(url).error(errorRes).placeholder(placeRes).into(imageView);
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);
}
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public static RequestManager with(android.app.Fragment fragment) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(fragment);
}
调用的也是重载方法，如果我们传入的Context,则会根据context判断重载哪个方法，如果传入的是Application类型，或者不是在主线程调用，则不处理。
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);
}
}
public RequestManager get(Fragment fragment) {
if (fragment.getActivity() == null) {
throw new IllegalArgumentException("You cannot start a load on a fragment before it is attached");
}
if (Util.isOnBackgroundThread()) {
return get(fragment.getActivity().getApplicationContext());
} else {
FragmentManager fm = fragment.getChildFragmentManager();
return supportFragmentGet(fragment.getActivity(), fm);
}
}
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public RequestManager get(Activity activity) {
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);
}
}
//如果绑的Fragment
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
public RequestManager get(android.app.Fragment fragment) {
if (fragment.getActivity() == null) {
throw new IllegalArgumentException("You cannot start a load on a fragment before it is attached");
}
if (Util.isOnBackgroundThread() || Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
return get(fragment.getActivity().getApplicationContext());
} else {
android.app.FragmentManager fm = fragment.getChildFragmentManager();
return fragmentGet(fragment.getActivity(), fm);
}
}
为什么这里要这么处理activity和fragement呢？因为glide会根据当前界面的生命周期去判断是否要下载，通常某个界面加载显示图片，退出当前界面后，如果还未加载成功则不需要再加载当前图片。glide就绑定activity的生命周期做相应的判断。glide怎么知道activity的生命周期呢?
如果在子线程中，或者SDK版本低于17，则绑定的是Application，生命周期无法控制
如果绑定的Fragment，Activity，则生成一个RequestManagerFragment，添加到Activity里面，这个Fragment没有UI，但是因为Fragment和Activity生命周期一致，所有就可以监听到Activity的生命周期
同理，support包里面的Fragment也是一样
关键代码如下，拿到FragmentManager,然后add进去。这样在Framgnet里面就可以监听Activity的生命周期了
RequestManagerFragment getRequestManagerFragment(
@NonNull final android.app.FragmentManager fm, @Nullable android.app.Fragment parentHint) {
RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
if (current == null) {
current = pendingRequestManagerFragments.get(fm);
if (current == null) {
current = new RequestManagerFragment();
current.setParentFragmentHint(parentHint);
pendingRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
总结:glide通过在activity 里面放入一个无UI的Fragment监听activity的生命周期方法。当然还要处理兼容版本
load 也是有很多重载方法，根测参数我们应该猜测出，它是可以从各种格式加载资源，包括网络，多媒体库中，本地文件，资源文件等等.
public DrawableTypeRequest load(String string) {
return (DrawableTypeRequest) fromString().load(string);
}
public DrawableTypeRequest load(Uri uri) {
return (DrawableTypeRequest) fromUri().load(uri);
}
public DrawableTypeRequest load(File file) {
return (DrawableTypeRequest) fromFile().load(file);
}
public DrawableTypeRequest load(Integer resourceId) {
return (DrawableTypeRequest) fromResource().load(resourceId);
}
public DrawableTypeRequest load(URL url) {
return (DrawableTypeRequest) fromUrl().load(url);
}
不管那个load方法，最终都会调用loadGeneric()方法。只不过传入的class类型不一样。
public DrawableTypeRequest fromString() {
return loadGeneric(String.class);
}
public DrawableTypeRequest fromUri() {
return loadGeneric(Uri.class);
}
public DrawableTypeRequest fromFile() {
return loadGeneric(File.class);
}
loadGeneric方法
private DrawableTypeRequest loadGeneric(Class modelClass) {
ModelLoader streamModelLoader = Glide.buildStreamModelLoader(modelClass, context);
ModelLoader 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(modelClass, streamModelLoader, fileDescriptorModelLoader, context,
glide, requestTracker, lifecycle, optionsApplier));
}
loadGeneric返回的是DrawableTypeRequest对象,调用DrawableTypeRequest对象的load方法。DrawableTypeRequest继承了DrawableRequestBuilder，load的方法也是继承。因此看DrawableRequestBuilder的load方法
DrawableRequestBuilder的load方法
@Override
public DrawableRequestBuilder load(ModelType model) {
super.load(model);
return this;
}
DrawableRequestBuilder调用父类GenericRequestBuilder的方法，好像没啥实质性的作用，其实它复写的目的就是可以链式调用，可以方便外部调用者使用。这点在写一个库或者组件或者sdk给外部调用者使用的时候就很有用，因为外部调用者就可以使用非常简洁的调用方式。
查看GenericRequestBuilder的load方法，比较简单，就是给变量model赋值了，并且isModelSet赋值true
public GenericRequestBuilder load(ModelType model) {
this.model = model;
isModelSet = true;
return this;
}
前面那个formString()怎么生成一个DrawableTypeRequest对象还没看，formString调用的是loadGeneric，参数的是String.class，因此我们看loadGeneric方法
private DrawableTypeRequest loadGeneric(Class modelClass) {
ModelLoader streamModelLoader = Glide.buildStreamModelLoader(modelClass, context);
ModelLoader 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(modelClass, streamModelLoader, fileDescriptorModelLoader, context,
glide, requestTracker, lifecycle, optionsApplier));
}
根据modelClass从Glide里面获取到一个ModelLoader实现类，因为ModelLoader是个接口，因此拿到的到底是哪个实现类，得从buildStreamModelLoader方法去找，T类型是String,
public static ModelLoader buildStreamModelLoader(Class modelClass, Context context) {
return buildModelLoader(modelClass, InputStream.class, context);
}
public static ModelLoader buildModelLoader(Class modelClass, Class 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);
}
调用了buildModelLoader,传入一个InputStram Class,这里T是String,Y是InputStram类型
public static ModelLoader buildModelLoader(T model, Class resourceClass, Context context) {
return buildModelLoader(model != null ? (Class) model.getClass() : null, resourceClass, context);
}
继续查看，这里又调用glide.getLoaderFactory返回的是GenericLoaderFactory类型，因此看GenericLoaderFactory的buildModelLoader方法。
public static ModelLoader buildModelLoader(Class modelClass, Class resourceClass,
Context context) {
return Glide.get(context).getLoaderFactory().buildModelLoader(modelClass, resourceClass);
}
GenericLoaderFactory的buildModelLoader方法，
public synchronized ModelLoader buildModelLoader(Class modelClass, Class resourceClass) {
//根据modelClass和resourceClass从缓存中查找ModelLoader，
ModelLoader result = getCachedLoader(modelClass, resourceClass);
...
//没有找到，就利用ModelLoaderFactory创建,这个ModelLoaderFactory又是从哪来?
final ModelLoaderFactory 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;
}
从getFactory里面可以看到modelClassToResourceFactories，保存了以modelClass类型的Class为key,Map为value，这么map又以resouceClass为key，value就是ModelLoaderFactory。也就是根据modelClass和resoouceClass最终才能获取到ModelLoaderFactory,
private ModelLoaderFactory getFactory(Class modelClass, Class resourceClass) {
Map 这里都是从Map里面获取的，那生成的这些对象在哪里？
在Glide的构造方法里面，生成这些对象，然后存放在GenericLoaderFactory的modelClassToResourceFactories集合中
Glide(Engine engine, MemoryCache memoryCache, BitmapPool bitmapPool, Context context, DecodeFormat decodeFormat) {
....
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());
//注释1 我们传入的是这两个类型
register(String.class, InputStream.class, new StreamStringLoader.Factory());
register(Uri.class, ParcelFileDescriptor.class, new FileDescriptorUriLoader.Factory());
//注释2 StreamUriLoader
register(Uri.class, InputStream.class, new StreamUriLoader.Factory());
register(URL.class, InputStream.class, new StreamUrlLoader.Factory());
//注释3
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);
}
由前面可知，modelClass是String类型，resouceClass是ParecelFileDescriptor类型。看注释1 知道后面的factory是StreamStringLoader的build生成的,里面又获取到一个根据modelClass和resouceClass生成另外一个ModelLoader传入进入
public class StreamStringLoader extends StringLoader implements StreamModelLoader {
public static class Factory implements ModelLoaderFactory {
@Override
public ModelLoader build(Context context, GenericLoaderFactory factories) {
return new StreamStringLoader(factories.buildModelLoader(Uri.class, InputStream.class));
}
@Override
public void teardown() {
// Do nothing.
}
}
public StreamStringLoader(Context context) {
this(Glide.buildStreamModelLoader(Uri.class, context));
}
public StreamStringLoader(ModelLoader uriLoader) {
super(uriLoader);
}
}
StringLoader主要是把String转换为Uri，然后如果解析Uri.交给它里面的uriLoader去处理。看Glide构造器注释2 可知，根据Uri.class和InputStream.class，拿到的是StreamUriLoader.Factory生成的类
public class StringLoader implements ModelLoader {
@Override
public DataFetcher getResourceFetcher(String model, int width, int height) {
Uri uri;
if (model.startsWith("/")) {
uri = toFileUri(model);
} else {
uri = Uri.parse(model);
final String scheme = uri.getScheme();
if (scheme == null) {
uri = toFileUri(model);
}
}
return uriLoader.getResourceFetcher(uri, width, height);
}
private static Uri toFileUri(String path) {
return Uri.fromFile(new File(path));
}
}
继续看StreamUriLoader类，继承UriLoader，并且又放入了一个ModelLoader，根据Glide注释3可知，该类是个HttpUrlGlideUrlLoader
public class StreamUriLoader extends UriLoader implements StreamModelLoader {
public static class Factory implements ModelLoaderFactory {
@Override
public ModelLoader build(Context context, GenericLoaderFactory factories) {
return new StreamUriLoader(context, factories.buildModelLoader(GlideUrl.class, InputStream.class));
}
@Override
public void teardown() {
// Do nothing.
}
}
...
}
在UriLoader里面就区别了，判断是Asset路径，还是ContentResolver路径。或者是url路径，然后再根据对应的DateFetcher去加载。由于我们传入的是url。因此看HttpUrlGlideUrlLoader的getResourceFetcher方法
public abstract class UriLoader implements ModelLoader {
private final Context context;
private final ModelLoader urlLoader;
public UriLoader(Context context, ModelLoader urlLoader) {
this.context = context;
this.urlLoader = urlLoader;
}
@Override
public final DataFetcher getResourceFetcher(Uri model, int width, int height) {
final String scheme = model.getScheme();
DataFetcher result = null;
if (isLocalUri(scheme)) {
if (AssetUriParser.isAssetUri(model)) {
String path = AssetUriParser.toAssetPath(model);
result = getAssetPathFetcher(context, path);
} else {
result = getLocalUriFetcher(context, model);
}
} else if (urlLoader != null && ("http".equals(scheme) || "https".equals(scheme))) {
result = urlLoader.getResourceFetcher(new GlideUrl(model.toString()), width, height);
}
return result;
}
protected abstract DataFetcher getLocalUriFetcher(Context context, Uri uri);
protected abstract DataFetcher getAssetPathFetcher(Context context, String path);
private static boolean isLocalUri(String scheme) {
return ContentResolver.SCHEME_FILE.equals(scheme)
|| ContentResolver.SCHEME_CONTENT.equals(scheme)
|| ContentResolver.SCHEME_ANDROID_RESOURCE.equals(scheme);
}
}
@Override
public DataFetcher getResourceFetcher(GlideUrl model, int width, int height) {
// GlideUrls memoize parsed URLs so caching them saves a few object instantiations and time spent parsing urls.
GlideUrl url = model;
if (modelCache != null) {
url = modelCache.get(model, 0, 0);
if (url == null) {
modelCache.put(model, 0, 0, model);
url = model;
}
}
return new HttpUrlFetcher(url);
}
最后返回的是个HttpUrlFetcher类.
小结：
根据glide构造器register这么多类可知，可以根据传入的modelClass和resouceClass可以获取后面那个factory生成的类。
streamModelLoader返回的是个StreamStringLoader类。调用getResourceFetcher返回的是个HttpUrlFetcher类
继续看loadGeneric方法，现在我们分析了buildStreamModelLoader方法。同理后面的buildFileDescriptorModelLoader方法也是，只不过这个T就是ParecelFileDescriptor类型，方法调用和上面一致，我们也就不再看，因为看后面的代码可知，先是用streamModelLoader返回的DataFetcher去加载，加载不到再用fileDescriptorModelLoader返回的DataFetcher去加载，streamModelLoader返回的DataFeccher加载返回的是个InputStream，fileDescriptorModelLoader返回的DataFetcher加载返回的是个ParcelFileDescriptor,至于这个ParcelFileDescriptor是干什么的，我们用的也比较少，有兴趣可以自行研究。
为什么对streamModelLoader和它的getResourceFetcher返回对象研究这么多，因为它这两个都是接口，如果不找到它对应的实现类，则看到后面的时候遇到它的方法调用，点到接口里面就看不到实现了。
private DrawableTypeRequest loadGeneric(Class modelClass) {
ModelLoader streamModelLoader = Glide.buildStreamModelLoader(modelClass, context);
ModelLoader fileDescriptorModelLoader =
Glide.buildFileDescriptorModelLoader(modelClass, context);
...
return optionsApplier.apply(
new DrawableTypeRequest(modelClass, streamModelLoader, fileDescriptorModelLoader, context,
glide, requestTracker, lifecycle, optionsApplier));
}
loadGeneric方法new 了一个DrawableTypeRequest返回。并且传入了streamModelLoader
继续看调用error方法。也是一样设置了加载失败资源文件。返回自身
@Override
public DrawableRequestBuilder error(int resourceId) {
super.error(resourceId);
return this;
}
调用placeholder也是一样。
@Override
public DrawableRequestBuilder placeholder(int resourceId) {
super.placeholder(resourceId);
return this;
}
最后调用into方法
public Target into(ImageView view) {
return super.into(view);
}
调用到 GenericRequestBuilder 类的into方法,如果在scaleType属性设置了,并且没有调用 transform方法，则表示不需要处理Bitamp,现在暂时看scaleType没有设置的情况.调用了glide的buildImageViewTarget方法，传入的是view和transcodeClass对象。那这个transcodeClass又是什么对象呢？
public Target into(ImageView view) {
//判断是否在主线程。不是则抛出异常
Util.assertMainThread();
if (view == null) {
throw new IllegalArgumentException("You must pass in a non null View");
}
//如果需要转换处理
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));
}
在构造方法里面赋值的
GenericRequestBuilder(Context context, Class modelClass,
LoadProvider loadProvider,
Class transcodeClass, Glide glide, RequestTracker requestTracker, Lifecycle lifecycle) {
this.context = context;
this.modelClass = modelClass;
this.transcodeClass = transcodeClass;
}
看子类DrawableTypeRequest的构造方法，GlideDrawable.class类型
DrawableTypeRequest(Class modelClass, ModelLoader streamModelLoader,
ModelLoader 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;
}
继续看glide的buildImageViewTarget里面调用的是buildTarget方法,由上面可知我们传入的是
GlideDrawable.class。因此。这里生成的对象就是GlideDrawableImageViewTarget对象
public Target buildTarget(ImageView view, Class clazz) {
if (GlideDrawable.class.isAssignableFrom(clazz)) {
return (Target) new GlideDrawableImageViewTarget(view);
} else if (Bitmap.class.equals(clazz)) {
return (Target) new BitmapImageViewTarget(view);
} else if (Drawable.class.isAssignableFrom(clazz)) {
return (Target) new DrawableImageViewTarget(view);
} else {
throw new IllegalArgumentException("Unhandled class: " + clazz
+ ", try .as*(Class).transcode(ResourceTranscoder)");
}
}
知道了target类型，继续看into的重载了方法，因为前面那个GlideDrawableImageViewTarget对象时直接new出来的，因此previous为null，调用buildRequest方法构建一个request
public > 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())");
}
//获取target里面的request。清楚和回收
Request previous = target.getRequest();
if (previous != null) {
previous.clear();
requestTracker.removeRequest(previous);
previous.recycle();
}
//构建requeset
Request request = buildRequest(target);
target.setRequest(request);
lifecycle.addListener(target);
requestTracker.runRequest(request);
return target;
}