Glide.with(Activity).load("http://xxxx").into(ImageView);
简单的一行代码，完成了从网络加载图片，并显示在对应的ImageView中，接下里让我们看下这短短的一行代码都干了啥
RequestManager：看名字应该是管理请求的类
public class Glide implements ComponentCallbacks2 {
public static RequestManager with(@NonNull Activity activity) {
return getRetriever(activity).get(activity);
}
看名字应该是获取RequestManager的获取者
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
...
return Glide.get(context).getRequestManagerRetriever();
}
初始化Glide
public static Glide get(@NonNull Context context) {
if (glide == null) {
GeneratedAppGlideModule annotationGeneratedModule =
getAnnotationGeneratedGlideModules(context.getApplicationContext());
synchronized (Glide.class) {
if (glide == null) {
//初始化Glide
checkAndInitializeGlide(context, annotationGeneratedModule);
}
}
}
return glide;
}
初始化Glide最后会调用来到initializeGlide方法
private static void initializeGlide(
@NonNull Context context,
@NonNull GlideBuilder builder,
@Nullable GeneratedAppGlideModule annotationGeneratedModule) {
//处理在AndroidManifest.xml中自定义的GlideModule，这招还是很骚的
Context applicationContext = context.getApplicationContext();
List<com.bumptech.glide.module.GlideModule> manifestModules = Collections.emptyList();
if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
manifestModules = new ManifestParser(applicationContext).parse();
}
if (annotationGeneratedModule != null
&& !annotationGeneratedModule.getExcludedModuleClasses().isEmpty()) {
Set<Class<?>> excludedModuleClasses = annotationGeneratedModule.getExcludedModuleClasses();
...
RequestManagerRetriever.RequestManagerFactory factory =
annotationGeneratedModule != null
? annotationGeneratedModule.getRequestManagerFactory()
: null;
builder.setRequestManagerFactory(factory);
for (com.bumptech.glide.module.GlideModule module : manifestModules) {
module.applyOptions(applicationContext, builder);
}
if (annotationGeneratedModule != null) {
annotationGeneratedModule.applyOptions(applicationContext, builder);
}
//创建Glide
Glide glide = builder.build(applicationContext);
...
Glide.glide = glide;
}
}
从代码中可以看到，Glide的初始化用的是Builder设计模式，这种设计模式的好处就是将一个复杂的对象的构建与表示相分离。将变与不变的部分分离，产品的组成部分不变，但每一部分都是灵活选择的。接下来我们看看Builder的build方法干了啥
Glide build(@NonNull Context context) {
if (sourceExecutor == null) {
sourceExecutor = GlideExecutor.newSourceExecutor();
}
...
if (bitmapPool == null) {
int size = memorySizeCalculator.getBitmapPoolSize();
if (size > 0) {
bitmapPool = new LruBitmapPool(size);
} else {
bitmapPool = new BitmapPoolAdapter();
}
}
...
if (engine == null) {
engine =
new Engine(
memoryCache,
diskCacheFactory,
diskCacheExecutor,
sourceExecutor,
GlideExecutor.newUnlimitedSourceExecutor(),
animationExecutor,
isActiveResourceRetentionAllowed);
}
if (defaultRequestListeners == null) {
defaultRequestListeners = Collections.emptyList();
} else {
defaultRequestListeners = Collections.unmodifiableList(defaultRequestListeners);
}
//创建RequstMangaerRetirever
RequestManagerRetriever requestManagerRetriever =
new RequestManagerRetriever(requestManagerFactory);
return new Glide(
context,
engine,
memoryCache,
bitmapPool,
arrayPool,
requestManagerRetriever,
connectivityMonitorFactory,
logLevel,
defaultRequestOptionsFactory,
defaultTransitionOptions,
defaultRequestListeners,
isLoggingRequestOriginsEnabled,
isImageDecoderEnabledForBitmaps);
}
从Builder的build方法可以看出，build方法其实就是初始化一些资源池与线程调度器，还有Engine，资源加载的引擎类，在后续的加载模块的文章中会讲到这个类。接下来我们看看Glide的构造方法
Glide(
@NonNull Context context,...) {
this.engine = engine;
this.bitmapPool = bitmapPool;
this.arrayPool = arrayPool;
this.memoryCache = memoryCache;
this.requestManagerRetriever = requestManagerRetriever;
this.connectivityMonitorFactory = connectivityMonitorFactory;
this.defaultRequestOptionsFactory = defaultRequestOptionsFactory;
final Resources resources = context.getResources();
registry = new Registry();
registry.register(new DefaultImageHeaderParser());
...
registry
.append(ByteBuffer.class, new ByteBufferEncoder())
.append(InputStream.class, new StreamEncoder(arrayPool))
/* Bitmaps */
.append(Registry.BUCKET_BITMAP, ByteBuffer.class, Bitmap.class, byteBufferBitmapDecoder)
.append(Registry.BUCKET_BITMAP, InputStream.class, Bitmap.class, streamBitmapDecoder);
...
}
Glide的构造方法中，注册了一大坨东西，咱们暂时先不要纠结这些，因为这些都是在后续Engine请求加载资源中会用到。接着看getRequestManagerRetriever做了啥
public RequestManagerRetriever getRequestManagerRetriever() {
return requestManagerRetriever;
}
就是放回了个成员变量，然后我们再看看RequestManagerRetriever的get(Activity)方法是如何获取到RequestManager的。
public RequestManager get(@NonNull Activity activity) {
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
} else {
assertNotDestroyed(activity);
android.app.FragmentManager fm = activity.getFragmentManager();
return fragmentGet(activity, fm, null, isActivityVisible(activity));
}
}
private RequestManager fragmentGet(
@NonNull Context context,
@NonNull android.app.FragmentManager fm,
@Nullable android.app.Fragment parentHint,
boolean isParentVisible) {
RequestManagerFragment current = getRequestManagerFragment(fm, parentHint, isParentVisible);
RequestManager requestManager = current.getRequestManager();
//尝试从RequestManagerFragment中获取RequestManager，不存在则创建一个新的RequestManager
if (requestManager == null) {
Glide glide = Glide.get(context);
requestManager =
factory.build(
glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
current.setRequestManager(requestManager);
}
return requestManager;
}
private RequestManagerFragment getRequestManagerFragment(
@NonNull final android.app.FragmentManager fm,
@Nullable android.app.Fragment parentHint,
boolean isParentVisible) {
//尝试在FragmentManager中获取到Tag为{FRAGMENT_TAG}的Fragment，不存在则创建
RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
if (current == null) {
current = pendingRequestManagerFragments.get(fm);
if (current == null) {
current = new RequestManagerFragment();
current.setParentFragmentHint(parentHint);
if (isParentVisible) {
current.getGlideLifecycle().onStart();
}
pendingRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
从代码中可以看出，首先通过FragmentManager来获取一个Tag为{FRAGMENT_TAG}的RequestManagerFragment，如果不存在就创建一个新的RequestManagerFragment，并且commit到FragmentManager中去，RequestManager同理。接下来我们看看RequestManager的load方法
public RequestBuilder<TranscodeType> load(@Nullable String string) {
return loadGeneric(string);
}
private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
this.model = model;
isModelSet = true;
return this;
}
load方法只是设置成员变量model的值而已，接下来看看RequestBuilder的into方法
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
...
return into(
glideContext.buildImageViewTarget(view, transcodeClass),
/*targetListener=*/ null,
requestOptions,
Executors.mainThreadExecutor());
}
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
BaseRequestOptions<?> options,
Executor callbackExecutor) {
...
Request request = buildRequest(target, targetListener, options, callbackExecutor);
requestManager.clear(target);
target.setRequest(request);
requestManager.track(target, request);
return target;
}
创建请求，然后启动请求。然后就完成了资源加载并作用到对应的View上了。接下来还会发表两篇文章一篇讲解Glide的智能管理请求，另外一篇讲解下Glide真的资源具体流程(Engine)
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