Glide原理之with过程

  本文基于Glide4.9.0版本讲解。

 Glide目前是Android开发中主流的图片加载框架。有必要花时间研究一下它的实现原理。因此，从本文开始将对Glide主要流程进行分析，由于Glide的加载链条比较长，便于理解我们分开分析，先分析Glide.with过程。

 1.Glide.with(FragmentActivity)

/**
   * 根据FragmentActivity获取Glide对象，并将加载过程跟FragmentActivity生命周期绑定。
   *
   * @param activity The activity to use.
   * @return A RequestManager for the given FragmentActivity that can be used to start a load.
   */
  @NonNull
  public static RequestManager with(@NonNull FragmentActivity activity) {
    return getRetriever(activity).get(activity);
  }

调用了getRetriever方法。

2. getRetriever方法

@NonNull
  private static RequestManagerRetriever getRetriever(@Nullable Context context) {
    // 检测context空对象，抛出异常
    Preconditions.checkNotNull(
        context,
        "You cannot start a load on a not yet attached View or a Fragment where getActivity() "
            + "returns null (which usually occurs when getActivity() is called before the Fragment "
            + "is attached or after the Fragment is destroyed).");
    return Glide.get(context).getRequestManagerRetriever();
  }


  /** Internal method. */
  @NonNull
  public RequestManagerRetriever getRequestManagerRetriever() {
    return requestManagerRetriever;
  }

根据getRequestManagerRetriever方法我们发现RequestManagerRetriever对象是在Glide类的属性，我们看一下get方法中是如何初始化的。

3. Glide.get方法

  /**
   * 单例
   *
   * @return the singleton
   */
  @NonNull
  public static Glide get(@NonNull Context context) {
    if (glide == null) {
      //获取注解生成的AppGlideModule
      GeneratedAppGlideModule annotationGeneratedModule =
          getAnnotationGeneratedGlideModules(context.getApplicationContext());
      synchronized (Glide.class) {
        if (glide == null) {
          checkAndInitializeGlide(context, annotationGeneratedModule);
        }
      }
    }

    return glide;
  }

3.1 getAnnotationGeneratedGlideModules

GeneratedAppGlideModule方法通过反射实例化AppGlideModule对象并返回。

  @Nullable
  @SuppressWarnings({"unchecked", "TryWithIdenticalCatches", "PMD.UnusedFormalParameter"})
  private static GeneratedAppGlideModule getAnnotationGeneratedGlideModules(Context context) {
    GeneratedAppGlideModule result = null;
    try {
      Class<GeneratedAppGlideModule> clazz =
          (Class<GeneratedAppGlideModule>)
              Class.forName("com.bumptech.glide.GeneratedAppGlideModuleImpl");
      result =
          clazz.getDeclaredConstructor(Context.class).newInstance(context.getApplicationContext());
    } catch (ClassNotFoundException e) {
      if (Log.isLoggable(TAG, Log.WARN)) {
        Log.w(
            TAG,
            "Failed to find GeneratedAppGlideModule. You should include an"
                + " annotationProcessor compile dependency on com.github.bumptech.glide:compiler"
                + " in your application and a @GlideModule annotated AppGlideModule implementation"
                + " or LibraryGlideModules will be silently ignored");
      }
      // These exceptions can't be squashed across all versions of Android.
    } catch (InstantiationException e) {
      throwIncorrectGlideModule(e);
    } catch (IllegalAccessException e) {
      throwIncorrectGlideModule(e);
    } catch (NoSuchMethodException e) {
      throwIncorrectGlideModule(e);
    } catch (InvocationTargetException e) {
      throwIncorrectGlideModule(e);
    }
    return result;
  }

4. checkAndInitializeGlide

get方法在返回Glide实例之前，需要在checkAndInitializaGlide方法中进行一些初始化的操作。

@GuardedBy("Glide.class")
  private static void checkAndInitializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    // In the thread running initGlide(), one or more classes may call Glide.get(context).
    // Without this check, those calls could trigger infinite recursion.
    //加入状态为控制并发初始化的情况
    if (isInitializing) {
      throw new IllegalStateException(
          "You cannot call Glide.get() in registerComponents(),"
              + " use the provided Glide instance instead");
    }
    isInitializing = true;
    initializeGlide(context, generatedAppGlideModule);
    isInitializing = false;
  }

5. initializeGlide(context, generatedAppGlideModule)

  @GuardedBy("Glide.class")
  private static void initializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    initializeGlide(context, new GlideBuilder(), generatedAppGlideModule);
  }

  @GuardedBy("Glide.class")
  @SuppressWarnings("deprecation")
  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();
    //1.注解生成的Module为空或者支持解析Manifest配置的Module，则创建ManifestParser解析Manifest中配置的Module
    if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
      manifestModules = new ManifestParser(applicationContext).parse();
    }
    //2.如果有注解生成的Module且屏蔽的Module集合不为空，则过率Manifest中配置的Module。
    if (annotationGeneratedModule != null
        && !annotationGeneratedModule.getExcludedModuleClasses().isEmpty()) {
      Set<Class<?>> excludedModuleClasses = annotationGeneratedModule.getExcludedModuleClasses();
      Iterator<com.bumptech.glide.module.GlideModule> iterator = manifestModules.iterator();
      while (iterator.hasNext()) {
        com.bumptech.glide.module.GlideModule current = iterator.next();
        if (!excludedModuleClasses.contains(current.getClass())) {
          continue;
        }
        if (Log.isLoggable(TAG, Log.DEBUG)) {
          Log.d(TAG, "AppGlideModule excludes manifest GlideModule: " + current);
        }
        iterator.remove();
      }
    }

    if (Log.isLoggable(TAG, Log.DEBUG)) {
      for (com.bumptech.glide.module.GlideModule glideModule : manifestModules) {
        Log.d(TAG, "Discovered GlideModule from manifest: " + glideModule.getClass());
      }
    }
    //3.初始化RequestManager的工厂对象，赋值给GlideBuilder
    RequestManagerRetriever.RequestManagerFactory factory =
        annotationGeneratedModule != null
            ? annotationGeneratedModule.getRequestManagerFactory()
            : null;
    builder.setRequestManagerFactory(factory);
    //4.依次回调用外部配置的Module中的applyOptions方法，实现GlideBuilder配置的修改。
    for (com.bumptech.glide.module.GlideModule module : manifestModules) {
      module.applyOptions(applicationContext, builder);
    }
    if (annotationGeneratedModule != null) {
      annotationGeneratedModule.applyOptions(applicationContext, builder);
    }
    //5.创建Glide对象
    Glide glide = builder.build(applicationContext);
    for (com.bumptech.glide.module.GlideModule module : manifestModules) {
      try {
        module.registerComponents(applicationContext, glide, glide.registry);
      } catch (AbstractMethodError e) {
        throw new IllegalStateException(
            "Attempting to register a Glide v3 module. If you see this, you or one of your"
                + " dependencies may be including Glide v3 even though you're using Glide v4."
                + " You'll need to find and remove (or update) the offending dependency."
                + " The v3 module name is: "
                + module.getClass().getName(),
            e);
      }
    }
    if (annotationGeneratedModule != null) {
      annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry);
    }
    //6. 注册Application 生命周期监听。内存紧张时把BitmapPool、MemoryCache和ArrayPool都清空
    applicationContext.registerComponentCallbacks(glide);
    Glide.glide = glide;
  }

6. GlideBuilder.build()

public final class GlideBuilder {
  //图片转换处理集合
  private final Map<Class<?>, TransitionOptions<?, ?>> defaultTransitionOptions = new ArrayMap<>();
  //图片加载引擎，负责启动并管理缓存资源
  private Engine engine;
  //Lru策略的图片池,内存不足时自动清空
  private BitmapPool bitmapPool;
  //Lru策略的数组池,用于读写IO,内存不足时自动清空
  private ArrayPool arrayPool;
  // Lru策略的内存缓存池,内存不足时自动清空
  private MemoryCache memoryCache;
  //线程池,用于查找内存缓存,最大线程数为4,具体取决于cpu
  private GlideExecutor sourceExecutor;
  //线程池,用于查找本地磁盘缓存,最大线程数为4,具体取决于cpu
  private GlideExecutor diskCacheExecutor;
  //用于创建本地磁盘缓存对象的工厂,默认本地磁盘缓存size为250M 
  private DiskCache.Factory diskCacheFactory;
  //内存计算器，它通过获取手机硬件常量和手机的屏幕密度、宽度和长度来计算出最适合当前情况的内存缓存的大小
  private MemorySizeCalculator memorySizeCalculator;
  //用于生产网络状态监听事件的工厂
  private ConnectivityMonitorFactory connectivityMonitorFactory;
  private int logLevel = Log.INFO;
  //设置Glide的配置选项
  private RequestOptionsFactory defaultRequestOptionsFactory =
      new RequestOptionsFactory() {
        @NonNull
        @Override
        public RequestOptions build() {
          return new RequestOptions();
        }
      };
  //用于创建RequestManager对象的工厂
  @Nullable private RequestManagerFactory requestManagerFactory;
  //线程池,用于加载gif图片,默认线程数为1~2,最大数取决于cpu的核数
  private GlideExecutor animationExecutor;
  // 是否将保留图片资源数据不给回收,默认为false 需要注意的是,设为true将会导致更大的内存消耗,增加crash的几率
  private boolean isActiveResourceRetentionAllowed;
  //全局网络请求集合，每次网络请求都会回调
  @Nullable private List<RequestListener<Object>> defaultRequestListeners;

  //...省略部分代码

  @NonNull
  Glide build(@NonNull Context context) {
    if (sourceExecutor == null) {
      sourceExecutor = GlideExecutor.newSourceExecutor();
    }

    if (diskCacheExecutor == null) {
      diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
    }

    if (animationExecutor == null) {
      animationExecutor = GlideExecutor.newAnimationExecutor();
    }

    if (memorySizeCalculator == null) {
      memorySizeCalculator = new MemorySizeCalculator.Builder(context).build();
    }

    if (connectivityMonitorFactory == null) {
      connectivityMonitorFactory = new DefaultConnectivityMonitorFactory();
    }

    if (bitmapPool == null) {
      int size = memorySizeCalculator.getBitmapPoolSize();
      if (size > 0) {
        bitmapPool = new LruBitmapPool(size);
      } else {
        bitmapPool = new BitmapPoolAdapter();
      }
    }

    if (arrayPool == null) {
      arrayPool = new LruArrayPool(memorySizeCalculator.getArrayPoolSizeInBytes());
    }

    if (memoryCache == null) {
      memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
    }

    if (diskCacheFactory == null) {
      diskCacheFactory = new InternalCacheDiskCacheFactory(context);
    }

    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);
    }
    //实例化RequestManagerRetriever对象，RequestManagerRetriever 是 Handler.CallBack 实现类，同时也是生命周期的一个管理类
    RequestManagerRetriever requestManagerRetriever =
        new RequestManagerRetriever(requestManagerFactory);

    return new Glide(
        context,
        engine,
        memoryCache,
        bitmapPool,
        arrayPool,
        requestManagerRetriever,
        connectivityMonitorFactory,
        logLevel,
        defaultRequestOptionsFactory,
        defaultTransitionOptions,
        defaultRequestListeners,
        isLoggingRequestOriginsEnabled,
        isImageDecoderEnabledForBitmaps,
        hardwareBitmapFdLimit);
  }
}

7. RequestManagerRetriever.get(FragmentActivity)

RequestManagerRetriever 是 Handler.CallBack 实现类，同时也是生命周期的一个管理类。

  @NonNull
  public RequestManager get(@NonNull FragmentActivity activity) {
    //是否在子线程运行
    if (Util.isOnBackgroundThread()) {
      //暂时忽略子线程启动的流程
      return get(activity.getApplicationContext());
    } else {
      //检查Activity是否被销毁
      assertNotDestroyed(activity);
      FragmentManager fm = activity.getSupportFragmentManager();
      //
      return supportFragmentGet(activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
    }
  }

8.RequestManagerRetriever.supportFragmentGet

  @NonNull
  private RequestManager supportFragmentGet(
      @NonNull Context context,
      @NonNull FragmentManager fm,
      @Nullable Fragment parentHint,
      boolean isParentVisible) {
    //获取监控FragmentActivity生命周期的Fragment
    SupportRequestManagerFragment current =
        getSupportRequestManagerFragment(fm, parentHint, isParentVisible);
    //获取SupportRequestManagerFragment中的RequestManager对象
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      //为空，重新创建一个并存到SupportRequestManagerFragment
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      current.setRequestManager(requestManager);
    }
    return requestManager;
  }


  @NonNull
  private SupportRequestManagerFragment getSupportRequestManagerFragment(
      @NonNull final FragmentManager fm, @Nullable Fragment parentHint, boolean isParentVisible) {
    //查找SupportRequestManagerFragment
    SupportRequestManagerFragment current =
        (SupportRequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
    if (current == null) {
      //若为空从缓存中取
      current = pendingSupportRequestManagerFragments.get(fm);
      if (current == null) {
        //依然为空则重新创建一个
        current = new SupportRequestManagerFragment();
        current.setParentFragmentHint(parentHint);
        //若Activity可见，回调生命周期监听
        if (isParentVisible) {
          current.getGlideLifecycle().onStart();
        }
        //缓存起来
        pendingSupportRequestManagerFragments.put(fm, current);
        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
        //发送消息,清空刚存进去的Fragment，这个地方没太理解为什么这样搞
        handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
      }
    }
    return current;
  }

创建了RequestManager，默认情况下使用DEFAULT_FACTORY

private static final RequestManagerFactory DEFAULT_FACTORY =
      new RequestManagerFactory() {
        @NonNull
        @Override
        public RequestManager build(
            @NonNull Glide glide,
            @NonNull Lifecycle lifecycle,
            @NonNull RequestManagerTreeNode requestManagerTreeNode,
            @NonNull Context context) {
          return new RequestManager(glide, lifecycle, requestManagerTreeNode, context);
        }
      };

到此，Glide 的 with(FragmentActivity) 的流程分析完成了。接下来分析load过程