ps：以下源碼分析基于Glide v4.11.0

Glide.jpg

涉及的類

主要涉及到以下這些類：

1. Glide，全局唯一
2. RequestManagerRetriever，用于獲取RequestManager
3. RequestManagerFragment/SupportRequestManagerFragment，用于提供生命周期
4. RequestManager，用于管理Request，內(nèi)部使用RequestTracker控制Reqeust的開始、暫停等
5. RequestTracker，控制Reqeust的開始、暫停等
6. Request，對應(yīng)著每一個圖片請求

數(shù)據(jù)處理的類型

1. Model：輸入類型，例如請求的url、某個圖片文件、資源drawableId等等?？梢詤⒖糆ngine的構(gòu)造函數(shù)中，Registry#append(...)添加的類型。
2. Data/DataClass：數(shù)據(jù)源返回的類型，例如InputStream、ParcelFileDescriptor、File、ByteBuffer等?？梢詤⒖糆ngine的構(gòu)造函數(shù)中，Registry#append(...)添加的類型。
3. Resource/ResourceType/TResource：中間類型，從數(shù)據(jù)源返回的類型Data編碼成的類型，例如Bitmap、Drawable、GifDrawable、BitmapDrawable、File等。舉個例子：例如由InputStream編碼成Bitmap?？梢詤⒖糆ngine的構(gòu)造函數(shù)中，Registry#append(...)添加的類型。
4. transcode：最終返回的類型。從Resource轉(zhuǎn)換成的類型，例如BitmapDrawable、byte[]。舉個例子：由Bitmap轉(zhuǎn)換成BitmapDrawable、由Bitmap轉(zhuǎn)換成byte[]。可以參考Engine的構(gòu)造函數(shù)中，Registry#register(...)添加的類型。

從使用方法作為入口進(jìn)行分析：

Glide.with(activity)
    .load(url)
    .into(targetView);

Glide

Glide，是全局唯一的，當(dāng)我們調(diào)用Glide#get(context)時，會去判斷是否已經(jīng)實例化，沒有的話會實例化。

// Glide.java
public static RequestManager with(@NonNull View view) {
    return getRetriever(view.getContext()).get(view);
}
  
@NonNull
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
    ...
    return Glide.get(context).getRequestManagerRetriever();
}

public static Glide get(@NonNull Context context) {
    if (glide == null) {
    
      // 獲取@GlideModule生成的GeneratedAppGlideModuleImpl類
      GeneratedAppGlideModule annotationGeneratedModule =
          getAnnotationGeneratedGlideModules(context.getApplicationContext());
      synchronized (Glide.class) {
        if (glide == null) {
          // 實例化Glide
          checkAndInitializeGlide(context, annotationGeneratedModule);
        }
      }
    }

    return glide;
}


private static void checkAndInitializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    
    if (isInitializing) {
      throw new IllegalStateException(
          "...");
    }
    isInitializing = true;
    initializeGlide(context, generatedAppGlideModule);
    isInitializing = false;
}


private static void initializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    initializeGlide(context, new GlideBuilder(), generatedAppGlideModule);
}


private static void initializeGlide(
      @NonNull Context context,
      @NonNull GlideBuilder builder,
      @Nullable GeneratedAppGlideModule annotationGeneratedModule) {
    Context applicationContext = context.getApplicationContext();
    List<com.bumptech.glide.module.GlideModule> manifestModules = Collections.emptyList();
    if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
      // 解析Manifest中注冊的自定義的GlideModule
      manifestModules = new ManifestParser(applicationContext).parse();
    }

    // ... 省略一些GlideModule和log相關(guān)的代碼

    RequestManagerRetriever.RequestManagerFactory factory =
        annotationGeneratedModule != null
            ? annotationGeneratedModule.getRequestManagerFactory()
            : null;
            
    // 設(shè)置RequestManagerFactory，后面用于創(chuàng)建RequestManager
    // 如果沒有@GlideModule生成的GeneratedAppGlideModuleImpl類，即factory為null，則使用RequestManagerRetriever類中的一個默認(rèn)Factory
    builder.setRequestManagerFactory(factory);
    
    // ... 省略應(yīng)用GlideModule相關(guān)代碼
    
    Glide glide = builder.build(applicationContext);
    
    // ... 省略應(yīng)用GlideModule相關(guān)代碼
    
    Glide.glide = glide;
}

Glide(
      @NonNull Context context,
      @NonNull Engine engine,
      @NonNull MemoryCache memoryCache,
      @NonNull BitmapPool bitmapPool,
      @NonNull ArrayPool arrayPool,
      @NonNull RequestManagerRetriever requestManagerRetriever,
      @NonNull ConnectivityMonitorFactory connectivityMonitorFactory,
      int logLevel,
      @NonNull RequestOptionsFactory defaultRequestOptionsFactory,
      @NonNull Map<Class<?>, TransitionOptions<?, ?>> defaultTransitionOptions,
      @NonNull List<RequestListener<Object>> defaultRequestListeners,
      boolean isLoggingRequestOriginsEnabled,
      boolean isImageDecoderEnabledForBitmaps) {
      
    this.engine = engine;
    
    // bitmap對象池
    this.bitmapPool = bitmapPool;
    
    // 數(shù)組對象池
    this.arrayPool = arrayPool;
    
    // 默認(rèn)是LruResourceCache
    this.memoryCache = memoryCache;
    
    // 用于根據(jù)參數(shù)（Application、Activity、FragmentActivity、Fragment、View）獲取RequestManager，詳見RequestManagerRetriever章節(jié)
    this.requestManagerRetriever = requestManagerRetriever;
    
    // 內(nèi)置了一系列的Entry，包含了ModelClass、DataClass、TransocdeClass、Encoder、Decoder、Transcoder等
    registry = new Registry();
    
    // Decoder
    ResourceDecoder<ByteBuffer, Bitmap> byteBufferBitmapDecoder;
    ResourceDecoder<InputStream, Bitmap> streamBitmapDecoder;
    if (isImageDecoderEnabledForBitmaps && Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
      streamBitmapDecoder = new InputStreamBitmapImageDecoderResourceDecoder();
      byteBufferBitmapDecoder = new ByteBufferBitmapImageDecoderResourceDecoder();
    } else {
      byteBufferBitmapDecoder = new ByteBufferBitmapDecoder(downsampler);
      streamBitmapDecoder = new StreamBitmapDecoder(downsampler, arrayPool);
    }
    
    // 創(chuàng)建ModelLoader的Factory，這里的StreamFactory創(chuàng)建的的是ModelLoader的子類ResourceLoader
    ResourceLoader.StreamFactory resourceLoaderStreamFactory =
        new ResourceLoader.StreamFactory(resources);
        
    // Transcoder
    BitmapBytesTranscoder bitmapBytesTranscoder = new BitmapBytesTranscoder();
    
    // 注冊Encoder
    registry
        .append(ByteBuffer.class, new ByteBufferEncoder())
        .append(InputStream.class, new StreamEncoder(arrayPool));
    
    // 注冊Decoder
    registry.append(Registry.BUCKET_BITMAP, ByteBuffer.class, Bitmap.class, byteBufferBitmapDecoder);
    
    // 注冊創(chuàng)建ModelLoader的Factory
    registry
        .append(int.class, InputStream.class, resourceLoaderStreamFactory)
        
    ...
    
    // 根據(jù)TranscodeClass創(chuàng)建ImageViewTarget的工廠類
    ImageViewTargetFactory imageViewTargetFactory = new ImageViewTargetFactory();
    
    // 用于之后獲取Registry等對象
    glideContext =
        new GlideContext(
            context,
            arrayPool,
            registry,
            imageViewTargetFactory,
            defaultRequestOptionsFactory,
            defaultTransitionOptions,
            defaultRequestListeners,
            engine,
            isLoggingRequestOriginsEnabled,
            logLevel);
      
}

// GlideBuilder.java
Glide build(@NonNull Context context) {
    
    ...
    
    // 用來獲取RequestManager對象（內(nèi)部使用RequestManagerFactory創(chuàng)建RequestManager）
    RequestManagerRetriever requestManagerRetriever =
        new RequestManagerRetriever(requestManagerFactory);
        
    ...
    
    return new Glide(
        context,
        engine,
        memoryCache,
        bitmapPool,
        arrayPool,
        requestManagerRetriever,
        connectivityMonitorFactory,
        logLevel,
        defaultRequestOptionsFactory,
        defaultTransitionOptions,
        defaultRequestListeners,
        isLoggingRequestOriginsEnabled,
        isImageDecoderEnabledForBitmaps);
}