Glide基本用法

基于glide4.7.1

Glide.with(context).load(obj).into(imageView)

• 先上图，with方法的流程图，看完图对基本流程有个了解，再细看代码

Glide初始化之with()解析.jpg

• 这是跟Glide初始化相关的类图

  
  
  Glide初始化相关的类.png

• 先看Glide的with(context)方法的实现, 根据传入的参数有以下方法的重载，发现都会调用getRetriever(context).get(context)方法,拆成两部分来看
  • 第一部分，getRetriever(context)负责Glide的初始化工作，并返回RequestManagerRetriever对象。
  • 第二部分，requestManagerRetriever.get(context),request请求如何绑定生命周期。

  public static RequestManager with(@NonNull Context context) {
    return getRetriever(context).get(context);
  }

  public static RequestManager with(@NonNull Activity activity) {
    return getRetriever(activity).get(activity);
  }

  public static RequestManager with(@NonNull FragmentActivity activity) {
    return getRetriever(activity).get(activity);
  }

  public static RequestManager with(@NonNull Fragment fragment) {
    return getRetriever(fragment.getActivity()).get(fragment);
  }

  public static RequestManager with(@NonNull android.app.Fragment fragment) {
    return getRetriever(fragment.getActivity()).get(fragment);
  }

  public static RequestManager with(@NonNull View view) {
    return getRetriever(view.getContext()).get(view);
  }

Glide的初始化过程

• getRetriever(context)方法调用了Glide的get(context)方法返回Glide对象，然后调用getRequestManagerRetriever()方法返回RequestManagerRetriever对象，因此初始化工作主要在Glide.get(context)中进行。

  private static RequestManagerRetriever getRetriever(@Nullable Context context) {
    ......
    return Glide.get(context).getRequestManagerRetriever();
  }

• 进入Glide的get(Context)方法，内部实现了一个单例模式，调用checkAndInitializeGlide(context)检查并初始化Glide对象。

  public static Glide get(@NonNull Context context) {
    if (glide == null) {
      synchronized (Glide.class) {
        if (glide == null) {
          checkAndInitializeGlide(context);
        }
      }
    }
    return glide;
  }

• 先判断初始化标志位是否已经被初始化了，如果不进行检查，可能出现多个类调用get(context)方法，同时调用初始化方法，这样就保证了单线程Glide只会被初始化一次。

  private static void checkAndInitializeGlide(@NonNull Context context) {
    if (isInitializing) {
      throw new IllegalStateException("You cannot call Glide.get() in registerComponents(),"
          + " use the provided Glide instance instead");
    }
    isInitializing = true;
    initializeGlide(context);
    isInitializing = false;
  }

• 进入initializeGlide(context)方法，new了一个GlideBuilder对象当做实参

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

• 这部分初始化主要进行了两部分工作
  因为Glide4支持自定义GlideModule，第一部分就是先获取我们创建的module，如果存在第二部分就会调用applyOptions方法，就我们新建的builder传入,从而可以让开发者自行配置参数，然后再调用builder.build(applicationContext)方法创建出Glide，开发者在builder中配置的参数也会被应用。最后调用
  annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry)方法注册Glide组件。

private static void initializeGlide(@NonNull Context context, @NonNull GlideBuilder builder) {
    Context applicationContext = context.getApplicationContext();
    // 获取自定义GlideModule
    GeneratedAppGlideModule annotationGeneratedModule = getAnnotationGeneratedGlideModules();
    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();
      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;
        }

        iterator.remove();
      }
    }

   // 第二部分初始化Glide，为module注册组件和应用参数设置
    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);
    }

    // 构建出glide对象
    Glide glide = builder.build(applicationContext);
    for (com.bumptech.glide.module.GlideModule module : manifestModules) {
      module.registerComponents(applicationContext, glide, glide.registry);
    }
    if (annotationGeneratedModule != null) {
      annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry);
    }
    applicationContext.registerComponentCallbacks(glide);
    Glide.glide = glide;
  }

• 从上面得知glide是通过调用GlideBuilder中的build方法构建的。通过下面代码可以看出，如果我们没有在自定义的module中配置，在build中都会配置默认参数
  下面这些配置的参数对应的类都可以对照上面的类图
  • 先创建了两个线程池一个用于根据数据源加载图片，一个从缓存中加载图片
  • 计算缓存Bitmap缓存池内存大小，并且根据大小创建Bitamp缓存池
  • 创建数组对象池
  • 创建加载引擎
  • 创建需要返回的requestManagerRetriever
  • 调用构造函数，new 一个Glide对象，初始化完毕。

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

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

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

    // 自己深入了解看看
    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());
    }

    RequestManagerRetriever requestManagerRetriever = new RequestManagerRetriever(
        requestManagerFactory);

    return new Glide(
        context,
        engine,
        memoryCache,
        bitmapPool,
        arrayPool,
        requestManagerRetriever,
        connectivityMonitorFactory,
        logLevel,
        defaultRequestOptions.lock(),
        defaultTransitionOptions);
  }

• 综上,Glide第一部分初始化已经完成。
  
  

Glide生命周期的绑定

• 在RequestManagerRetriever中get()有多个方法重载
  • 共同点：判断是不是在后台线程，如果在后台线程直接走Application生命周期
  • 如果传入的是context,会根据FragmentActivity、Activity的实例还是ContextWrapper来调用对应的方法。
  • 如果传入的是FragmentActivity或者Fragment(来自v4包)，调用supportFragmentGet
  • 如果传入的是Activity(非v4包)，调用fragmentGet
  • 如果传入View通过调用view.getContext()对象进行判断，决定是调用fragmentGet还是supportFragmentGet
  • 通过上面分析关键方法就是supportFragmentGet或fragmentGet，两个方法实现逻辑基本一样，我们挑其中最常用的supportFragmentGet来看

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, null /*parentHint*/);
    }
  }

  public RequestManager get(Fragment fragment) {
    if (Util.isOnBackgroundThread()) {
      return get(fragment.getActivity().getApplicationContext());
    } else {
      FragmentManager fm = fragment.getChildFragmentManager();
      return supportFragmentGet(fragment.getActivity(), fm, fragment);
    }
  }

  public RequestManager get(Activity activity) {
    if (Util.isOnBackgroundThread()) {
      return get(activity.getApplicationContext());
    } else {
      assertNotDestroyed(activity);
      android.app.FragmentManager fm = activity.getFragmentManager();
      return fragmentGet(activity, fm, null /*parentHint*/);
    }
  }

  public RequestManager get(View view) {
    if (Util.isOnBackgroundThread()) {
      return get(view.getContext().getApplicationContext());
    }

    Activity activity = findActivity(view.getContext());

    if (activity == null) {
      return get(view.getContext().getApplicationContext());
    }

    if (activity instanceof FragmentActivity) {
      Fragment fragment = findSupportFragment(view, (FragmentActivity) activity);
      if (fragment == null) {
        return get(activity);
      }
      return get(fragment);
    }

    android.app.Fragment fragment = findFragment(view, activity);
    if (fragment == null) {
      return get(activity);
    }
    return get(fragment);
  }

• 干了两件事情
• 调用getSupportRequestManagerFragment获取Fragment
• 调用factory.build(glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode())创建 了RequestManager对象

  private RequestManager supportFragmentGet(Context context, FragmentManager fm,
      Fragment parentHint) {
    SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm, parentHint);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode());
      current.setRequestManager(requestManager);
    }
    return requestManager;
  }

• 通过Tag来查找Fragment，如果找不到，就从等待队列中找，如果还是没有就创建一个,加入等待对列中，将Fragment和Activity绑定，并使用handler发送消息从队列中移除Fragment。

  SupportRequestManagerFragment getSupportRequestManagerFragment(
      final FragmentManager fm, Fragment parentHint) {
    SupportRequestManagerFragment current =
        (SupportRequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
    if (current == null) {
      current = pendingSupportRequestManagerFragments.get(fm);
      if (current == null) {
        current = new SupportRequestManagerFragment();
        current.setParentFragmentHint(parentHint);
        pendingSupportRequestManagerFragments.put(fm, current);
        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
        handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
      }
    }
    return current;
  }

• SupportRequestManagerFragment的构造函数创建了一个ActivityFragmentLifecycle对象用来管理生命周期，在onStart方法中调用ActivityFragmentLifecycle的onStart方法，同理其他生命周期方法也是。

public class SupportRequestManagerFragment extends Fragment {
  public SupportRequestManagerFragment() {
    this(new ActivityFragmentLifecycle());
  }

  @VisibleForTesting
  @SuppressLint("ValidFragment")
  public SupportRequestManagerFragment(@NonNull ActivityFragmentLifecycle lifecycle) {
    this.lifecycle = lifecycle;
  }

  @Override
  public void onStart() {
    super.onStart();
    lifecycle.onStart();
  }

  @Override
  public void onStop() {
    super.onStop();
    lifecycle.onStop();
  }

  @Override
  public void onDestroy() {
    super.onDestroy();
    lifecycle.onDestroy();
    unregisterFragmentWithRoot();
  }
    
}

• 下面来看RequestManger是如何构造的并绑定了Fragment的生命周期
  • factory.build(glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode())，current就是我们上面的SupportRequestManagerFragment对象，将和他绑定的生命周期对象Lifecycle传给了RequestManger构造函数

 public RequestManager build(Glide glide, Lifecycle lifecycle,
        RequestManagerTreeNode requestManagerTreeNode) {
      return new RequestManager(glide, lifecycle, requestManagerTreeNode);
    }

• 在RequestManager实现了LifecycleListener接口，并且调用lifecycle.addListener(this)添加监听器。接口生命周期函数onStart()启动请求，onStop暂停请求

public class RequestManager implements LifecycleListener {
  RequestManager(
      Glide glide,
      Lifecycle lifecycle,
      RequestManagerTreeNode treeNode,
      RequestTracker requestTracker,
      ConnectivityMonitorFactory factory) {
    this.glide = glide;
    this.lifecycle = lifecycle;
    this.treeNode = treeNode;
    this.requestTracker = requestTracker;

    final Context context = glide.getGlideContext().getBaseContext();

    connectivityMonitor =
        factory.build(context, new RequestManagerConnectivityListener(requestTracker));

    if (Util.isOnBackgroundThread()) {
      mainHandler.post(addSelfToLifecycle);
    } else {
      lifecycle.addListener(this);
    }
    lifecycle.addListener(connectivityMonitor);

    setRequestOptions(glide.getGlideContext().getDefaultRequestOptions());

    glide.registerRequestManager(this);
  }

 @Override
  public void onStart() {
    resumeRequests();
    targetTracker.onStart();
  }

  @Override
  public void onStop() {
    pauseRequests();
    targetTracker.onStop();
  }

 
}

• 在ActivtyFragmentLifecycle中如果添加了监听器，在onStart调用监听器的onStart方法，也就是调用RequsetManager中的onStart，同理onPause也是。

class ActivityFragmentLifecycle implements Lifecycle {
  @Override
  public void addListener(LifecycleListener listener) {
    lifecycleListeners.add(listener);

    if (isDestroyed) {
      listener.onDestroy();
    } else if (isStarted) {
      listener.onStart();
    } else {
      listener.onStop();
    }
  }

  @Override
  public void removeListener(LifecycleListener listener) {
    lifecycleListeners.remove(listener);
  }

  void onStart() {
    isStarted = true;
    for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
      lifecycleListener.onStart();
    }
  }

  void onStop() {
    isStarted = false;
    for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
      lifecycleListener.onStop();
    }
  }

  void onDestroy() {
    isDestroyed = true;
    for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
      lifecycleListener.onDestroy();
    }
  }
}

• 经过上面的分析发现整个过程就理顺了，先创建一个Fragment对象并在构造函数中创建Lifecycle对象
  ，在创建RequestManager的时候会把Lifecycle对象传递进去。
• RequestManger则在构造函数处为接收的Lifecycle添加监听器，而RequestManager自身实现了LifecycleListener，在实现的接口方法onStop和onPause分别启动和暂停请求。
• Lifecycle对象在添加监听器后，会在生命周期方法onStart和onPauser分别调用监听器对应的方法。
• 因此当Fragment会在生命周期方法中调用Lifecycle对应的生命周期方法，最终也就是在调用RequestManger中的生命周期方法，因此实现了请求和生命周期的绑定，从而可以根据生命周期来启动和暂停请求。

• 总结一下，with()方法主要初始化Glide和创建了RequestManger绑定SupportRequestManagerFragment的生命周期函数，最后返回RequestManager。