> For the complete documentation index, see [llms.txt](https://android.malinkang.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://android.malinkang.com/network/glide-source.md).

# Glide源码分析

`Glide`的使用非常简单只需要调用`with`、`load` `into`三个方法。

```java
 GlideApp.with(this)
        .load(url)
        .into(imageView);
```

接下来，我们依次分析这三个方法。

## with()

```java
//Glide.java
public static RequestManager with(@NonNull Activity activity) {
  //先获取RequestManagerRetriever对象
  //调用RequestManagerRetriever的get方法获取RequestManager
  return getRetriever(activity).get(activity); 
}
private static RequestManagerRetriever getRetriever(@Nullable Context context) {
  // Context could be null for other reasons (ie the user passes in null), but in practice it will
  // only occur due to errors with the Fragment lifecycle.
  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();
}

```

### get()

```java
@NonNull
public static Glide get(@NonNull Context context) {
  if (glide == null) {
    //获取生成的GdlieModule类
    GeneratedAppGlideModule annotationGeneratedModule =
        getAnnotationGeneratedGlideModules(context.getApplicationContext());
    synchronized (Glide.class) {
      if (glide == null) {
        //初始化Glide
        checkAndInitializeGlide(context, annotationGeneratedModule);
      }
    }
  }
  return glide;
}
```

### ApiGlideModule

`ApiGlideModule`定义了在应用程序中初始化 `Glide` 时要使用的一系列依赖关系和选项。

![](/files/-MH0s6vfRGrSRyzJTpKS)

```java
//GeneratedAppGlideModuleImpl
 @Override
 @NonNull
 GeneratedRequestManagerFactory getRequestManagerFactory() {
   return new GeneratedRequestManagerFactory();
 }
```

### checkAndInitializeGlide()

```java
@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.
    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;
}
```

### initializeGlide()

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

```java
  @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();
    if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
      //解析ManifestParser 老的Glide版本需要在清单文件中注册GlideModule
      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;
        }
        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());
      }
    }
    //获取RequestManagerFactory即GeneratedRequestManagerFactory
    RequestManagerRetriever.RequestManagerFactory factory =
        annotationGeneratedModule != null
            ? annotationGeneratedModule.getRequestManagerFactory()
            : null;
    //为GlideBuilder设置RequestManagerFactory
    builder.setRequestManagerFactory(factory);
    for (com.bumptech.glide.module.GlideModule module : manifestModules) {
      module.applyOptions(applicationContext, builder);
    }
    if (annotationGeneratedModule != null) {
      annotationGeneratedModule.applyOptions(applicationContext, builder);
    }
    //调用build方法创建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);
    }
    applicationContext.registerComponentCallbacks(glide);
    Glide.glide = glide;
  }
```

### GlideBuilder

```java
  @NonNull
  Glide build(@NonNull Context context) {
    if (sourceExecutor == null) {
      sourceExecutor = GlideExecutor.newSourceExecutor();
    }
    //执行硬盘缓存的线程池
    if (diskCacheExecutor == null) {
      diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
    }
    //动画线程池
    if (animationExecutor == null) {
      animationExecutor = GlideExecutor.newAnimationExecutor();
    }
    //内存大小计算
    if (memorySizeCalculator == null) {
      memorySizeCalculator = new MemorySizeCalculator.Builder(context).build();
    }
    //创建默认连接监听工厂
    if (connectivityMonitorFactory == null) {
      connectivityMonitorFactory = new DefaultConnectivityMonitorFactory();
    }
    //除了ArrayPool之外每个缓存都有两个版本。
    //LruBitmapPool BitmapPoolAdapter
    //LruResourceCache MemoryCacheAdapter
    //DiskLruCacheWrapper DiskCacheAdapter
    //当内存不足的时候调用XXAdapter，put方法里什么也不做
    // 正常调用LruXX
    //BitmapPool
    if (bitmapPool == null) {
      int size = memorySizeCalculator.getBitmapPoolSize();
      if (size > 0) {
        bitmapPool = new LruBitmapPool(size);
      } else {
        bitmapPool = new BitmapPoolAdapter();
      }
    }
    //ArrayPool
    if (arrayPool == null) {
      arrayPool = new LruArrayPool(memorySizeCalculator.getArrayPoolSizeInBytes());
    }
   //MemoryCache
    if (memoryCache == null) {
      memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
    }
    //DiskCacheFactory
    if (diskCacheFactory == null) {
      diskCacheFactory = new InternalCacheDiskCacheFactory(context);
    }
    //创建Engine
    if (engine == null) {
      engine =
          new Engine(
              memoryCache,
              diskCacheFactory,
              diskCacheExecutor,
              sourceExecutor,
              GlideExecutor.newUnlimitedSourceExecutor(),//无限制缓存池
              animationExecutor,
              isActiveResourceRetentionAllowed);
    }

    if (defaultRequestListeners == null) {
      defaultRequestListeners = Collections.emptyList();
    } else {
      defaultRequestListeners = Collections.unmodifiableList(defaultRequestListeners);
    }
    //创建RequestManagerRetriever
    RequestManagerRetriever requestManagerRetriever =
        new RequestManagerRetriever(
            requestManagerFactory, waitForFirstFrameBeforeEnablingHardwareBitmaps);

    boolean blockHardwareBitmaps =
        waitForFirstFrameBeforeEnablingHardwareBitmaps || waitForCallBeforeEnablingHardwareBitmaps;
    //调用Glide构造函数创建Glide对象
    return new Glide(
        context,
        engine,
        memoryCache,
        bitmapPool,
        arrayPool,
        requestManagerRetriever,
        connectivityMonitorFactory,
        logLevel,
        defaultRequestOptionsFactory,
        defaultTransitionOptions,
        defaultRequestListeners,
        isLoggingRequestOriginsEnabled,
        isImageDecoderEnabledForBitmaps,
        blockHardwareBitmaps,
        manualOverrideHardwareBitmapMaxFdCount);
  }
```

### GlideExecutor

在`build()`中一共创建了4个线程池

`newDiskCacheExecutor()`创建磁盘缓存的线程池

```java
  private static final int DEFAULT_DISK_CACHE_EXECUTOR_THREADS = 1;
  public static GlideExecutor newDiskCacheExecutor() {
    return newDiskCacheBuilder().build();
  }
  public static GlideExecutor.Builder newDiskCacheBuilder() {
    return new GlideExecutor.Builder(/*preventNetworkOperations=*/ true)
        .setThreadCount(DEFAULT_DISK_CACHE_EXECUTOR_THREADS) //线程数1
        .setName(DEFAULT_DISK_CACHE_EXECUTOR_NAME);
  }
```

其余三个线程池都是负责下载和解码的`newAnimationBuilder`是用来处理gif的。

```java
public final class GlideExecutor implements ExecutorService {
  private static final int MAXIMUM_AUTOMATIC_THREAD_COUNT = 4;
  
  public static GlideExecutor newSourceExecutor() {
    return newSourceBuilder().build();
  }
  public static GlideExecutor.Builder newSourceBuilder() {
    return new GlideExecutor.Builder(/*preventNetworkOperations=*/ false)
        .setThreadCount(calculateBestThreadCount())
        .setName(DEFAULT_SOURCE_EXECUTOR_NAME);
  }
  //计算最佳的线程数量
  public static int calculateBestThreadCount() {
    if (bestThreadCount == 0) {
      //cpu内核数量和4取最小值
      bestThreadCount =
          Math.min(MAXIMUM_AUTOMATIC_THREAD_COUNT, RuntimeCompat.availableProcessors());
    }
    return bestThreadCount;
  }
}
```

```java
  public static GlideExecutor.Builder newAnimationBuilder() {
    int bestThreadCount = calculateBestThreadCount();
    // We don't want to add a ton of threads running animations in parallel with our source and
    // disk cache executors. Doing so adds unnecessary CPU load and can also dramatically increase
    // our maximum memory usage. Typically one thread is sufficient here, but for higher end devices
    // with more cores, two threads can provide better performance if lots of GIFs are showing at
    // once.
    //我们不希望增加大量线程来并行运行动画，我们的源代码和磁盘缓存执行器。
    //这样做增加了不必要的CPU负载，也会大大增加了我们的最大内存使用量。
    //通常情况下，一个线程就足够了，但对于更高端的设备来说。
    //如果有更多的核心，两个线程可以提供更好的性能，如果大量的GIF显示一次。
    int maximumPoolSize = bestThreadCount >= 4 ? 2 : 1;

    return new GlideExecutor.Builder(/*preventNetworkOperations=*/ true)
        .setThreadCount(maximumPoolSize)
        .setName(DEFAULT_ANIMATION_EXECUTOR_NAME);
  }

  /** Shortcut for calling {@link Builder#build()} on {@link #newAnimationBuilder()}. */
  public static GlideExecutor newAnimationExecutor() {
    return newAnimationBuilder().build();
  }
```

```java
  public static GlideExecutor newUnlimitedSourceExecutor() {
    return new GlideExecutor(
        new ThreadPoolExecutor(
            0,
            Integer.MAX_VALUE,
            KEEP_ALIVE_TIME_MS,
            TimeUnit.MILLISECONDS,
            new SynchronousQueue<Runnable>(),
            new DefaultThreadFactory(
                DEFAULT_SOURCE_UNLIMITED_EXECUTOR_NAME, UncaughtThrowableStrategy.DEFAULT, false)));
  }
```

这三个线程池选用哪个呢？

```java
  //EngineJob.java
  private GlideExecutor getActiveSourceExecutor() {
    return useUnlimitedSourceGeneratorPool
        ? sourceUnlimitedExecutor
        : (useAnimationPool ? animationExecutor : sourceExecutor);
  }
```

`useUnlimitedSourceGeneratorsPool`和`useAnimationPool`可以通过`BaseRequestOptions`进行配置。

```java
  private boolean useUnlimitedSourceGeneratorsPool;
  private boolean useAnimationPool;
  @NonNull
  @CheckResult
  public T useAnimationPool(boolean flag) {
    if (isAutoCloneEnabled) {
      return clone().useAnimationPool(flag);
    }

    useAnimationPool = flag;
    fields |= USE_ANIMATION_POOL;

    return selfOrThrowIfLocked();
  }
  
```

`useAnimationPool`默认不需要配置。系统默认会在处理gif的时候设置为true。

```java
  //GifFrameLoader.java
  private static RequestBuilder<Bitmap> getRequestBuilder(
      RequestManager requestManager, int width, int height) {
    return requestManager
        .asBitmap()
        .apply(
            diskCacheStrategyOf(DiskCacheStrategy.NONE)
                .useAnimationPool(true)
                .skipMemoryCache(true)
                .override(width, height));
  }
```

### MemorySizeCalculator

```java
  public static final class Builder {
    @VisibleForTesting static final int MEMORY_CACHE_TARGET_SCREENS = 2;

    /**
     * On Android O+, we use {@link android.graphics.Bitmap.Config#HARDWARE} for all reasonably
     * sized images unless we're creating thumbnails for the first time. As a result, the Bitmap
     * pool is much less important on O than it was on previous versions.
     */
    static final int BITMAP_POOL_TARGET_SCREENS =
        Build.VERSION.SDK_INT < Build.VERSION_CODES.O ? 4 : 1;

    static final float MAX_SIZE_MULTIPLIER = 0.4f;
    static final float LOW_MEMORY_MAX_SIZE_MULTIPLIER = 0.33f;
    // 4MB.
    static final int ARRAY_POOL_SIZE_BYTES = 4 * 1024 * 1024;

    @Synthetic final Context context;

    // Modifiable (non-final) for testing.
    @Synthetic ActivityManager activityManager;
    @Synthetic ScreenDimensions screenDimensions;

    @Synthetic float memoryCacheScreens = MEMORY_CACHE_TARGET_SCREENS;
    @Synthetic float bitmapPoolScreens = BITMAP_POOL_TARGET_SCREENS;
    @Synthetic float maxSizeMultiplier = MAX_SIZE_MULTIPLIER;
    @Synthetic float lowMemoryMaxSizeMultiplier = LOW_MEMORY_MAX_SIZE_MULTIPLIER;
    @Synthetic int arrayPoolSizeBytes = ARRAY_POOL_SIZE_BYTES;
 }
```

```java
// Package private to avoid PMD warning.
  MemorySizeCalculator(MemorySizeCalculator.Builder builder) {
    this.context = builder.context;
    //4M 低内存设备2M
    arrayPoolSize =
        isLowMemoryDevice(builder.activityManager)
            ? builder.arrayPoolSizeBytes / LOW_MEMORY_BYTE_ARRAY_POOL_DIVISOR
            : builder.arrayPoolSizeBytes;
    //计算最大大小
    int maxSize =
        getMaxSize(
            builder.activityManager, builder.maxSizeMultiplier, builder.lowMemoryMaxSizeMultiplier);

    int widthPixels = builder.screenDimensions.getWidthPixels();
    int heightPixels = builder.screenDimensions.getHeightPixels();
    //计算一张格式为 ARGB_8888 ，大小为屏幕大小的图片的占用内存大小
    //BYTES_PER_ARGB_8888_PIXEL 值为 4
    int screenSize = widthPixels * heightPixels * BYTES_PER_ARGB_8888_PIXEL;
    //BitmapPool大小
    //BitmapPool和MemoryCache的大小依赖当前屏幕分辨率
    int targetBitmapPoolSize = Math.round(screenSize * builder.bitmapPoolScreens);
    //MemoryCache大小 
    int targetMemoryCacheSize = Math.round(screenSize * builder.memoryCacheScreens);
    int availableSize = maxSize - arrayPoolSize;
    //小于可用大小 按照计算的值分配
    if (targetMemoryCacheSize + targetBitmapPoolSize <= availableSize) {
      memoryCacheSize = targetMemoryCacheSize;
      bitmapPoolSize = targetBitmapPoolSize;
    } else {
      //将可用的分配
      float part = availableSize / (builder.bitmapPoolScreens + builder.memoryCacheScreens);
      memoryCacheSize = Math.round(part * builder.memoryCacheScreens);
      bitmapPoolSize = Math.round(part * builder.bitmapPoolScreens);
    }
  }
```

```java
  private static int getMaxSize(
      ActivityManager activityManager, float maxSizeMultiplier, float lowMemoryMaxSizeMultiplier) {
    final int memoryClassBytes = activityManager.getMemoryClass() * 1024 * 1024;
    final boolean isLowMemoryDevice = isLowMemoryDevice(activityManager);
    return Math.round(
        memoryClassBytes * (isLowMemoryDevice ? lowMemoryMaxSizeMultiplier : maxSizeMultiplier));
  }
```

### 磁盘缓存

![](/files/-MH1e_RoVe9LlwIy3RMe)

```java
public final class InternalCacheDiskCacheFactory extends DiskLruCacheFactory {

  public InternalCacheDiskCacheFactory(Context context) {
    this(
        context,
        DiskCache.Factory.DEFAULT_DISK_CACHE_DIR,
        DiskCache.Factory.DEFAULT_DISK_CACHE_SIZE);
  }

  public InternalCacheDiskCacheFactory(Context context, long diskCacheSize) {
    this(context, DiskCache.Factory.DEFAULT_DISK_CACHE_DIR, diskCacheSize);
  }

  public InternalCacheDiskCacheFactory(
      final Context context, final String diskCacheName, long diskCacheSize) {
    super(
        new CacheDirectoryGetter() {
          @Override
          public File getCacheDirectory() {
            File cacheDirectory = context.getCacheDir();
            if (cacheDirectory == null) {
              return null;
            }
            if (diskCacheName != null) {
              return new File(cacheDirectory, diskCacheName);
            }
            return cacheDirectory;
          }
        },
        diskCacheSize);
  }
}
```

```java
 interface Factory {
    /** 250 MB of cache. */
    int DEFAULT_DISK_CACHE_SIZE = 250 * 1024 * 1024;

    String DEFAULT_DISK_CACHE_DIR = "image_manager_disk_cache";

    /** Returns a new disk cache, or {@code null} if no disk cache could be created. */
    @Nullable
    DiskCache build();
  }
```

### get()

```java
  @NonNull
  public RequestManager get(@NonNull Activity activity) {
    //获取RequestManager
    if (Util.isOnBackgroundThread()) {
      return get(activity.getApplicationContext());
    } else if (activity instanceof FragmentActivity) {
      return get((FragmentActivity) activity);
    } else {
      assertNotDestroyed(activity);
      maybeRegisterFirstFrameWaiter(activity);
      android.app.FragmentManager fm = activity.getFragmentManager();
      return fragmentGet(activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
    }
  }
```

### Lifecycle

Glide会添加一个透明的Fragment，当Fragment执行生命周期方法时，回调`Lifecycle`注册的`LifecycleListener`。

![](/files/-MH59U3hSRE73qh-kzpE)

```java
@Deprecated
  @NonNull
  private RequestManager fragmentGet(
      @NonNull Context context,
      @NonNull android.app.FragmentManager fm,
      @Nullable android.app.Fragment parentHint,
      boolean isParentVisible) {
    //创建RequestManagerFragment
    RequestManagerFragment current = getRequestManagerFragment(fm, parentHint);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      //将Lifecycle和RequestManagerTreeNode传递给RequestManager
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      // This is a bit of hack, we're going to start the RequestManager, but not the
      // corresponding Lifecycle. It's safe to start the RequestManager, but starting the
      // Lifecycle might trigger memory leaks. See b/154405040
      if (isParentVisible) {
        requestManager.onStart();
      }
      current.setRequestManager(requestManager);
    }
    return requestManager;
  }
```

```java
  @SuppressWarnings("deprecation")
  @NonNull
  private RequestManagerFragment getRequestManagerFragment(
      @NonNull final android.app.FragmentManager fm, @Nullable android.app.Fragment parentHint) {
    RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
    if (current == null) {
      //从Map中获取RequestManagerFragment
      current = pendingRequestManagerFragments.get(fm);
      if (current == null) {
        //创建ReqeustManagerFragment
        //创建Fragment的时候创建Lifecycle
        current = new RequestManagerFragment();
        current.setParentFragmentHint(parentHint);
        pendingRequestManagerFragments.put(fm, current);
        //添加fragment
        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
        handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
      }
    }
    return current;
  }
```

```java
  public RequestManagerFragment() {
    this(new ActivityFragmentLifecycle());
  }
```

### LifecycleListener

![](/files/-MH58V3W0LvmhT8nxdkY)

### RequestManager

在`RequestManager`中将当前对象和`DefaultConnectivityMonitor`和注册到`Lifecycle`。

```java
  private final Runnable addSelfToLifecycle =
      new Runnable() {
        @Override
        public void run() {
          lifecycle.addListener(RequestManager.this);
        }
      };
  private final ConnectivityMonitor connectivityMonitor;
  // Adding default listeners should be much less common than starting new requests. We want
  // some way of making sure that requests don't mutate our listeners without creating a new copy of
  // the list each time a request is started.
  private final CopyOnWriteArrayList<RequestListener<Object>> defaultRequestListeners;

  @GuardedBy("this")
  private RequestOptions requestOptions;

  private boolean pauseAllRequestsOnTrimMemoryModerate;

  public RequestManager(
      @NonNull Glide glide,
      @NonNull Lifecycle lifecycle,
      @NonNull RequestManagerTreeNode treeNode,
      @NonNull Context context) {
    this(
        glide,
        lifecycle,
        treeNode,
        new RequestTracker(),
        glide.getConnectivityMonitorFactory(),
        context);
  }

  // Our usage is safe here.
  @SuppressWarnings("PMD.ConstructorCallsOverridableMethod")
  RequestManager(
      Glide glide,
      Lifecycle lifecycle,
      RequestManagerTreeNode treeNode,
      RequestTracker requestTracker,
      ConnectivityMonitorFactory factory,
      Context context) {
    this.glide = glide;
    this.lifecycle = lifecycle;
    this.treeNode = treeNode;
    this.requestTracker = requestTracker;
    this.context = context;

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

    // If we're the application level request manager, we may be created on a background thread.
    // In that case we cannot risk synchronously pausing or resuming requests, so we hack around the
    // issue by delaying adding ourselves as a lifecycle listener by posting to the main thread.
    // This should be entirely safe.
    if (Util.isOnBackgroundThread()) {
      Util.postOnUiThread(addSelfToLifecycle);
    } else {
      lifecycle.addListener(this);
    }
    //添加
    lifecycle.addListener(connectivityMonitor);

    defaultRequestListeners =
        new CopyOnWriteArrayList<>(glide.getGlideContext().getDefaultRequestListeners());
    setRequestOptions(glide.getGlideContext().getDefaultRequestOptions());

    glide.registerRequestManager(this);
  }

```

## load()

通过`with()`方法返回了一个`RequestManager`对象，所以`load()`方法调用的是`RequestManager`的`load()`方法。

```java
@NonNull
@CheckResult
@Override
public RequestBuilder<Drawable> load(@Nullable String string) {
  return asDrawable().load(string);
}
@NonNull
@CheckResult
public RequestBuilder<Drawable> asDrawable() {
  return as(Drawable.class);
}
@NonNull
@CheckResult
public <ResourceType> RequestBuilder<ResourceType> as(
    @NonNull Class<ResourceType> resourceClass) {
    //创建RequestBuilder
  return new RequestBuilder<>(glide, this, resourceClass, context);
}
```

### RequestBuilder

![](/files/-MH5HOL7-vgPM062hdaG)

## into()

`load()`比较简单就是创建一个`RequestBuilder`对象。`into()`方法就是调用`RequestBuilder`的`into()`。

```java
 @NonNull
  public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
    Util.assertMainThread();
    Preconditions.checkNotNull(view);

    BaseRequestOptions<?> requestOptions = this;
    if (!requestOptions.isTransformationSet()
        && requestOptions.isTransformationAllowed()
        && view.getScaleType() != null) {
      // Clone in this method so that if we use this RequestBuilder to load into a View and then
      // into a different target, we don't retain the transformation applied based on the previous
      // View's scale type.
      switch (view.getScaleType()) {
        case CENTER_CROP:
          requestOptions = requestOptions.clone().optionalCenterCrop();
          break;
        case CENTER_INSIDE:
          requestOptions = requestOptions.clone().optionalCenterInside();
          break;
        case FIT_CENTER:
        case FIT_START:
        case FIT_END:
          requestOptions = requestOptions.clone().optionalFitCenter();
          break;
        case FIT_XY:
          requestOptions = requestOptions.clone().optionalCenterInside();
          break;
        case CENTER:
        case MATRIX:
        default:
          // Do nothing.
      }
    }

    return into(
        glideContext.buildImageViewTarget(view, transcodeClass),
        /*targetListener=*/ null,
        requestOptions,
        Executors.mainThreadExecutor());
  }
```

```java
  private <Y extends Target<TranscodeType>> Y into(
      @NonNull Y target,
      @Nullable RequestListener<TranscodeType> targetListener,
      BaseRequestOptions<?> options,
      Executor callbackExecutor) {
    Preconditions.checkNotNull(target);
    if (!isModelSet) {
      throw new IllegalArgumentException("You must call #load() before calling #into()");
    }
    //构建Request
    Request request = buildRequest(target, targetListener, options, callbackExecutor);

    Request previous = target.getRequest();
    if (request.isEquivalentTo(previous)
        && !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
      // If the request is completed, beginning again will ensure the result is re-delivered,
      // triggering RequestListeners and Targets. If the request is failed, beginning again will
      // restart the request, giving it another chance to complete. If the request is already
      // running, we can let it continue running without interruption.
      if (!Preconditions.checkNotNull(previous).isRunning()) {
        // Use the previous request rather than the new one to allow for optimizations like skipping
        // setting placeholders, tracking and un-tracking Targets, and obtaining View dimensions
        // that are done in the individual Request.
        previous.begin();
      }
      return target;
    }

    requestManager.clear(target);
    target.setRequest(request);
    //追踪Request
    requestManager.track(target, request);

    return target;
  }
```

### obtainRequest()

```java
  private Request obtainRequest(
      Object requestLock,
      Target<TranscodeType> target,
      RequestListener<TranscodeType> targetListener,
      BaseRequestOptions<?> requestOptions,
      RequestCoordinator requestCoordinator,
      TransitionOptions<?, ? super TranscodeType> transitionOptions,
      Priority priority,
      int overrideWidth,
      int overrideHeight,
      Executor callbackExecutor) {
    return SingleRequest.obtain(
        context,
        glideContext,
        requestLock,
        model,
        transcodeClass,
        requestOptions,
        overrideWidth,
        overrideHeight,
        priority,
        target,
        targetListener,
        requestListeners,
        requestCoordinator,
        glideContext.getEngine(),
        transitionOptions.getTransitionFactory(),
        callbackExecutor);
  }
```

### Request

![](/files/-MH5NU3forjNJlagwOfj)

![整体流程](/files/-MH5NQTyFWyTaToxXebn)

![第一次加载网络图片的编解码过程](/files/-MHF9mkgRwNalRMHWEQ7)

### 缓存过程

```java
//从缓存中获取
@Nullable
private EngineResource<?> loadFromMemory(
    EngineKey key, boolean isMemoryCacheable, long startTime) {
  //内存缓存不可用直接返回null
  if (!isMemoryCacheable) {
    return null;
  }
  //先从弱引用中获取，如果获取不到则从LruResourceCache中获取缓存
  EngineResource<?> active = loadFromActiveResources(key);
  if (active != null) {
    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Loaded resource from active resources", startTime, key);
    }
    return active;
  }

  EngineResource<?> cached = loadFromCache(key);
  if (cached != null) {
    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Loaded resource from cache", startTime, key);
    }
    return cached;
  }
  return null;
}
@Nullable
private EngineResource<?> loadFromActiveResources(Key key) {
  //从弱引用中获取
  EngineResource<?> active = activeResources.get(key);
  if (active != null) {
    active.acquire();
  }
  return active;
}
private EngineResource<?> loadFromCache(Key key) {
  EngineResource<?> cached = getEngineResourceFromCache(key);
  if (cached != null) {
    cached.acquire();
    activeResources.activate(key, cached);
  }
  return cached;
}
private EngineResource<?> getEngineResourceFromCache(Key key) {
  //从LruResourceCache中获取缓存
  Resource<?> cached = cache.remove(key);
  final EngineResource<?> result;
  if (cached == null) {
    result = null;
  } else if (cached instanceof EngineResource) {
    // Save an object allocation if we've cached an EngineResource (the typical case).
    result = (EngineResource<?>) cached;
  } else {
    result =
        new EngineResource<>(
            cached, /*isMemoryCacheable=*/ true, /*isRecyclable=*/ true, key, /*listener=*/ this);
  }
  return result;
}
//写入缓存
@Override
public synchronized void onResourceReleased(Key cacheKey, EngineResource<?> resource) {
  activeResources.deactivate(cacheKey);
  if (resource.isMemoryCacheable()) {
    cache.put(cacheKey, resource);
  } else {
    resourceRecycler.recycle(resource);
  }
}
```

````

### ModelLoader

`ModelLoader`类负责将`model`转换为`data`。`model`就是我们在调用`load`方法传入的值。

### getLoadData\(\)

```java
  //
  List<LoadData<?>> getLoadData() {
    if (!isLoadDataSet) {
      isLoadDataSet = true; //获取成功之后设置为true 避免多次获取
      loadData.clear();
      //根据Model获取ModelLoader
      List<ModelLoader<Object, ?>> modelLoaders = glideContext.getRegistry().getModelLoaders(model);
      //noinspection ForLoopReplaceableByForEach to improve perf
      for (int i = 0, size = modelLoaders.size(); i < size; i++) {
        ModelLoader<Object, ?> modelLoader = modelLoaders.get(i);
        LoadData<?> current = modelLoader.buildLoadData(model, width, height, options);
        if (current != null) {
          loadData.add(current);
        }
      }
    }
    return loadData;
  }
````

### getModelLoaders()

```java
  @NonNull
  public <Model> List<ModelLoader<Model, ?>> getModelLoaders(@NonNull Model model) {
    return modelLoaderRegistry.getModelLoaders(model);
  }
```

```java
  @NonNull
  public <A> List<ModelLoader<A, ?>> getModelLoaders(@NonNull A model) {
    List<ModelLoader<A, ?>> modelLoaders = getModelLoadersForClass(getClass(model));
    if (modelLoaders.isEmpty()) {
      throw new NoModelLoaderAvailableException(model);
    }
    int size = modelLoaders.size();
    boolean isEmpty = true;
    List<ModelLoader<A, ?>> filteredLoaders = Collections.emptyList();
    //noinspection ForLoopReplaceableByForEach to improve perf
    for (int i = 0; i < size; i++) {
      ModelLoader<A, ?> loader = modelLoaders.get(i);
      if (loader.handles(model)) {
        if (isEmpty) {
          filteredLoaders = new ArrayList<>(size - i);
          isEmpty = false;
        }
         //根据ModelLoader的handles方法，过滤掉不匹配的
        //假设传入的是url，则过滤掉DataUrlLoader
        filteredLoaders.add(loader);
      }
    }
    if (filteredLoaders.isEmpty()) {
      throw new NoModelLoaderAvailableException(model, modelLoaders);
    }
    return filteredLoaders;
  }
```

```java
  @NonNull
  private synchronized <A> List<ModelLoader<A, ?>> getModelLoadersForClass(
      @NonNull Class<A> modelClass) {
    //从缓存中取
    List<ModelLoader<A, ?>> loaders = cache.get(modelClass);
    if (loaders == null) {
      //调用MultiModelLoaderFactory的build方法
      loaders = Collections.unmodifiableList(multiModelLoaderFactory.build(modelClass));
      cache.put(modelClass, loaders);
    }
    return loaders;
  }
```

```java
  @NonNull
  synchronized <Model> List<ModelLoader<Model, ?>> build(@NonNull Class<Model> modelClass) {
    try {
      List<ModelLoader<Model, ?>> loaders = new ArrayList<>();
      for (Entry<?, ?> entry : entries) {
        // Avoid stack overflow recursively creating model loaders by only creating loaders in
        // recursive requests if they haven't been created earlier in the chain. For example:
        // A Uri loader may translate to another model, which in turn may translate back to a Uri.
        // The original Uri loader won't be provided to the intermediate model loader, although
        // other Uri loaders will be.
        if (alreadyUsedEntries.contains(entry)) {
          continue;
        }
        //根据ModelClass进行判断
        if (entry.handles(modelClass)) {
          alreadyUsedEntries.add(entry);
          //调用Factory创建Loader
          loaders.add(this.<Model, Object>build(entry));
          alreadyUsedEntries.remove(entry);
        }
      }
      return loaders;
    } catch (Throwable t) {
      alreadyUsedEntries.clear();
      throw t;
    }
  }
```

```java
//StringLoader先将String转化为Uri
//通过MultiModelLoaderFactory获取一个MultiModelLoader对象
//内部调用的MultiModelLoader
public static class StreamFactory implements ModelLoaderFactory<String, InputStream> {

    @NonNull
    @Override
    public ModelLoader<String, InputStream> build(@NonNull MultiModelLoaderFactory multiFactory) {
      return new StringLoader<>(multiFactory.build(Uri.class, InputStream.class));
    }

    @Override
    public void teardown() {
      // Do nothing.
    }
}
```

```java
  @NonNull
  public synchronized <Model, Data> ModelLoader<Model, Data> build(
      @NonNull Class<Model> modelClass, @NonNull Class<Data> dataClass) {
    try {
      List<ModelLoader<Model, Data>> loaders = new ArrayList<>();
      boolean ignoredAnyEntries = false;
      for (Entry<?, ?> entry : entries) {
        // Avoid stack overflow recursively creating model loaders by only creating loaders in
        // recursive requests if they haven't been created earlier in the chain. For example:
        // A Uri loader may translate to another model, which in turn may translate back to a Uri.
        // The original Uri loader won't be provided to the intermediate model loader, although
        // other Uri loaders will be.
        if (alreadyUsedEntries.contains(entry)) {
          ignoredAnyEntries = true;
          continue;
        }
        if (entry.handles(modelClass, dataClass)) {
          alreadyUsedEntries.add(entry);
          loaders.add(this.<Model, Data>build(entry));
          alreadyUsedEntries.remove(entry);
        }
      }
      //如果存在多个就构建成一个MultiModelLoader
      if (loaders.size() > 1) {
        return factory.build(loaders, throwableListPool);
      } else if (loaders.size() == 1) {
        return loaders.get(0);
      } else {
        // Avoid crashing if recursion results in no loaders available. The assertion is supposed to
        // catch completely unhandled types, recursion may mean a subtype isn't handled somewhere
        // down the stack, which is often ok.
        if (ignoredAnyEntries) {
          return emptyModelLoader();
        } else {
          throw new NoModelLoaderAvailableException(modelClass, dataClass);
        }
      }
    } catch (Throwable t) {
      alreadyUsedEntries.clear();
      throw t;
    }
  }
```

```java
  static class Factory {
    @NonNull
    public <Model, Data> MultiModelLoader<Model, Data> build(
        @NonNull List<ModelLoader<Model, Data>> modelLoaders,
        @NonNull Pool<List<Throwable>> throwableListPool) {
      return new MultiModelLoader<>(modelLoaders, throwableListPool);
    }
  }
```

### 加载到内存的图片大小

默认大小为`ImageView`的大小。设置了`override`，则是设置的大小。如果设置值为`Target.SIZE_ORIGINAL`，则使用图片原始大小。

```java
//SingleRequest begin方法
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
    onSizeReady(overrideWidth, overrideHeight);
} else {
    target.getSize(this);
}
//ViewTarget getSize方法
public void getSize(@NonNull SizeReadyCallback cb) {
    sizeDeterminer.getSize(cb);
}
//SizeDeterminer getSize方法
void getSize(@NonNull SizeReadyCallback cb) {
    int currentWidth = getTargetWidth(); //获取宽
    int currentHeight = getTargetHeight(); //获取高
    if (isViewStateAndSizeValid(currentWidth, currentHeight)) {
        cb.onSizeReady(currentWidth, currentHeight);
        return;
    }

    // We want to notify callbacks in the order they were added and we only expect one or two
    // callbacks to be added a time, so a List is a reasonable choice.
    if (!cbs.contains(cb)) {
        cbs.add(cb);
    }
    if (layoutListener == null) {
        ViewTreeObserver observer = view.getViewTreeObserver();
        layoutListener = new SizeDeterminerLayoutListener(this);
        observer.addOnPreDrawListener(layoutListener);
    }
}
//CustomTarget默认是原图大小
public CustomTarget() {
    this(Target.SIZE_ORIGINAL, Target.SIZE_ORIGINAL);
}
//Downsampler decodeFromWrappedStreams方法
//获取图片的原始宽高
int[] sourceDimensions = getDimensions(is, options, callbacks, bitmapPool);
int sourceWidth = sourceDimensions[0];
int sourceHeight = sourceDimensions[1];
//如果设置Target.SIZE_ORIGINAL 则为原始宽高
int targetWidth = requestedWidth == Target.SIZE_ORIGINAL ? sourceWidth : requestedWidth;
int targetHeight = requestedHeight == Target.SIZE_ORIGINAL ? sourceHeight : requestedHeight;
```

###

## 参考

* [Glide中文文档](https://muyangmin.github.io/glide-docs-cn/)
* [面试官：简历上最好不要写Glide，不是问源码那么简单](https://juejin.im/post/6844903986412126216)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://android.malinkang.com/network/glide-source.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.