探索Android开源框架 - 4. Glide使用及源码解析

2021-10-15 本文已影响0人今阳说

使用

1. 添加依赖

implementation 'com.github.bumptech.glide:glide:4.12.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.12.0'

2. 基础使用

加载图片

Glide.with(this)
    .load(imgUrl)
    .into(imageView1)

取消加载

Glide.with(this).clear(imageView1)

实际上，当 Glide.with() 中传入的 Activity 或 Fragment 实例销毁时，Glide 会自动取消加载并回收资源；

3. 进阶操作

更多的可选配置

Glide.with(this)//上下文对象Context
    .load(imgUrl)//图片地址
    .placeholder(R.mipmap.ic_launcher)//加载前的占位图
    .error(R.mipmap.ic_launcher)//加载失败的占位图
    .override(150,100)//指定图片尺寸(一般不用设置，Glide会自动根据ImageView的大小来决定图片的大小)
    .skipMemoryCache(true)//跳过内存缓存
    .diskCacheStrategy(DiskCacheStrategy.AUTOMATIC)//根据图片资源智能地选择使用哪一种缓存策略（默认选项）
    .diskCacheStrategy(DiskCacheStrategy.ALL)//既缓存原始图片，也缓存转换过的图片
    .diskCacheStrategy(DiskCacheStrategy.DATA)//只缓存原始图片
    .diskCacheStrategy(DiskCacheStrategy.RESOURCE)//只缓存转换过的图片
    .diskCacheStrategy(DiskCacheStrategy.NONE)//禁用磁盘缓存
    .priority(Priority.HIGH)//优先级
    .thumbnail(
        Glide.with(this).load(imgUrl).override(20)
    ) //设置缩略图
    .thumbnail(0.25f)//压缩原图为缩略图
    .into(ivGlide2)

更多的可选配置可以参考官方文档

通过 RequestOptions 共享配置

val options = RequestOptions()
    .placeholder(R.mipmap.ic_launcher)
    .error(R.mipmap.ic_launcher)
Glide.with(this)
    .load(imgUrl)
    .apply(options)
    .into(imageView1)
Glide.with(this)
    .load(imgUrl)
    .apply(options)
    .into(imageView2)

源码解析

源码方面主要从最基本的三个方法入手：with，load，into

1. with

Glide.with源码如下，根据不同上下文对象有多个重载方法，首先通过getRetriever方法获取RequestManagerRetriever对象，再通过get方法获取RequestManager实例

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.getContext()).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);
}

getRetriever方法中通过Glide.get通过懒汉式+双重校验锁获取Glide单例,再通过getter方法获取requestManagerRetriever属性；

private static RequestManagerRetriever getRetriever(@Nullable Context context) {
    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();
}

获取Glide实例

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

真正创建并初始化Glide实例实在initializeGlide方法, 调用GlideBuilder.build方法通过建造者模式创建Glide实例

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

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();
    ...
    Glide glide = builder.build(applicationContext);
    ...
    Glide.glide = glide;
}

GlideBuilder.build方法代码如下

Glide build(@NonNull Context context) {
    //获取图片的线程池
    if (sourceExecutor == null) {
      sourceExecutor = GlideExecutor.newSourceExecutor();
    }
    //磁盘缓存的线程池
    if (diskCacheExecutor == null) {
      diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
    }
    //动画的线程池
    if (animationExecutor == null) {
      animationExecutor = GlideExecutor.newAnimationExecutor();
    }
    //创建内存大小控制器
    if (memorySizeCalculator == null) {
      memorySizeCalculator = new MemorySizeCalculator.Builder(context).build();
    }
    //创建网络监听的工厂
    if (connectivityMonitorFactory == null) {
      connectivityMonitorFactory = new DefaultConnectivityMonitorFactory();
    }

    if (bitmapPool == null) {
      int size = memorySizeCalculator.getBitmapPoolSize();
      if (size > 0) {
        // 使用缓存，则创建bitmap对象池
        bitmapPool = new LruBitmapPool(size);
      } else {
        // 不使用缓存
        bitmapPool = new BitmapPoolAdapter();
      }
    }
    //创建对象数组缓存池
    if (arrayPool == null) {
      arrayPool = new LruArrayPool(memorySizeCalculator.getArrayPoolSizeInBytes());
    }
    //创建内存缓存
    if (memoryCache == null) {
      memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
    }
    //创建硬盘缓存工厂
    if (diskCacheFactory == null) {
      diskCacheFactory = new InternalCacheDiskCacheFactory(context);
    }
    //创建引擎类
    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);
    }

    GlideExperiments experiments = glideExperimentsBuilder.build();
    //创建请求管理类，其构造方法中会实例化一个主线程的handler对象，用于线程的切换
    RequestManagerRetriever requestManagerRetriever =
        new RequestManagerRetriever(requestManagerFactory, experiments);

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

上面代码中RequestManagerRetriever的构造方法如下

public RequestManagerRetriever(
      @Nullable RequestManagerFactory factory, GlideExperiments experiments) {
    this.factory = factory != null ? factory : DEFAULT_FACTORY;
    handler = new Handler(Looper.getMainLooper(), this /* Callback */);
    frameWaiter = buildFrameWaiter(experiments);
}

RequestManagerRetriever.get

上面通过glide单例获取RequestManagerRetriever实例，下面再调用其get方法获取RequestManager实例，也是有多个重载方法

public RequestManager get(@NonNull Context context) {
    //context判空及实际类型判断
    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
          && ((ContextWrapper) context).getBaseContext().getApplicationContext() != null) {
        return get(((ContextWrapper) context).getBaseContext());
      }
    }
    return getApplicationManager(context);
}

public RequestManager get(@NonNull FragmentActivity activity) {
    if (Util.isOnBackgroundThread()) {
      return get(activity.getApplicationContext());
    } else {
      ...
      FragmentManager fm = activity.getSupportFragmentManager();
      return supportFragmentGet(activity, fm, /*parentHint=*/ null, isActivityVisible(activity));
    }
}

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

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

 public RequestManager get(@NonNull View view) {
    ...
    Activity activity = findActivity(view.getContext());
    if (activity == null) {
      return get(view.getContext().getApplicationContext());
    }
    if (activity instanceof FragmentActivity) {
      Fragment fragment = findSupportFragment(view, (FragmentActivity) activity);
      return fragment != null ? get(fragment) : get((FragmentActivity) activity);
    }
    android.app.Fragment fragment = findFragment(view, activity);
    if (fragment == null) {
      return get(activity);
    }
    return get(fragment);
}

最终会调用supportFragmentGet或fragmentGet获取requestManager实例,其中会创建一个Fragment，那么我们就知道了glide是通过在内部维护一个fragment来管理生命周期的

private RequestManager supportFragmentGet(
      @NonNull Context context,
      @NonNull FragmentManager fm,
      @Nullable Fragment parentHint,
      boolean isParentVisible) {
    SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm, parentHint);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      if (isParentVisible) {
        requestManager.onStart();
      }
      current.setRequestManager(requestManager);
    }
    return requestManager;
}

private RequestManager fragmentGet(
      @NonNull Context context,
      @NonNull android.app.FragmentManager fm,
      @Nullable android.app.Fragment parentHint,
      boolean isParentVisible) {
    RequestManagerFragment current = getRequestManagerFragment(fm, parentHint);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      if (isParentVisible) {
        requestManager.onStart();
      }
      current.setRequestManager(requestManager);
    }
    return requestManager;
}

2. load

此时的load其实已经是RequestManager.load方法，也是有多个重载方法，可以传入不同的图片源

public RequestBuilder<Drawable> load(@Nullable Bitmap bitmap) {
    return asDrawable().load(bitmap);
}
public RequestBuilder<Drawable> load(@Nullable Drawable drawable) {
    return asDrawable().load(drawable);
}
public RequestBuilder<Drawable> load(@Nullable String string) {
    return asDrawable().load(string);
}
public RequestBuilder<Drawable> load(@Nullable Uri uri) {
    return asDrawable().load(uri);
}
public RequestBuilder<Drawable> load(@Nullable File file) {
    return asDrawable().load(file);
}
public RequestBuilder<Drawable> load(@RawRes @DrawableRes @Nullable Integer resourceId) {
    return asDrawable().load(resourceId);
}
public RequestBuilder<Drawable> load(@Nullable URL url) {
    return asDrawable().load(url);
}
public RequestBuilder<Drawable> load(@Nullable byte[] model) {
    return asDrawable().load(model);
}
public RequestBuilder<Drawable> load(@Nullable Object model) {
    return asDrawable().load(model);
}

上面代码中都会先调用asDrawable()，那么我们先来看看他是个啥

asDrawable()

asDrawable代码如下，其中只是调用as方法并传入Drawable.class, 再看看as方法，原来是创建一个图片类型为Drawable类型的RequestBuilder请求

public RequestBuilder<Drawable> asDrawable() {
    return as(Drawable.class);
}

public <ResourceType> RequestBuilder<ResourceType> as(
      @NonNull Class<ResourceType> resourceClass) {
    return new RequestBuilder<>(glide, this, resourceClass, context);
}

而且我们发现还要相似的asBitmap，asGif

public RequestBuilder<GifDrawable> asGif() {
    return as(GifDrawable.class).apply(DECODE_TYPE_GIF);
}

public RequestBuilder<Bitmap> asBitmap() {
    return as(Bitmap.class).apply(DECODE_TYPE_BITMAP);
}

现在我们知道了RequestManager.load是通过获取RequestBuilder实例，再调用其load方法

RequestBuilder.load

RequestBuilder.load也是有多个重载方法,但其中都是调用loadGeneric方法

public RequestBuilder<TranscodeType> load(@Nullable String string) {
    return loadGeneric(string);
}
public RequestBuilder<TranscodeType> load(@Nullable Uri uri) {
    return loadGeneric(uri);
}
public RequestBuilder<TranscodeType> load(@Nullable File file) {
    return loadGeneric(file);
}
public RequestBuilder<TranscodeType> load(@Nullable Drawable drawable) {
    return loadGeneric(drawable).apply(diskCacheStrategyOf(DiskCacheStrategy.NONE));
}
public RequestBuilder<TranscodeType> load(@Nullable Bitmap bitmap) {
    return loadGeneric(bitmap).apply(diskCacheStrategyOf(DiskCacheStrategy.NONE));
}
public RequestBuilder<TranscodeType> load(@RawRes @DrawableRes @Nullable Integer resourceId) {
    return loadGeneric(resourceId).apply(signatureOf(AndroidResourceSignature.obtain(context)));
}

loadGeneric代码如下,主要是将图片源保存起来，并设置是否设置了图片源的标识isModelSet = true,最后返回了RequestBuilder自身this

private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
    if (isAutoCloneEnabled()) {
      return clone().loadGeneric(model);
    }
    this.model = model;
    isModelSet = true;
    return selfOrThrowIfLocked();
}

protected final T selfOrThrowIfLocked() {
    if (isLocked) {
      throw new IllegalStateException("You cannot modify locked T, consider clone()");
    }
    return self();
}

private T self() {
    return (T) this;
}

3. into

接下来是通过RequestBuilder.into方法设置目标view

public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
    Util.assertMainThread();//断言是在主线程调用的
    Preconditions.checkNotNull(view);//非空判断
    BaseRequestOptions<?> requestOptions = this;
    if (!requestOptions.isTransformationSet()
        && requestOptions.isTransformationAllowed()
        && view.getScaleType() != null) {
      //熟悉的ScaleType们
      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());
}

最终是将view通过buildImageViewTarget方法转为target,transcodeClass为Bitmap.class或Drawable.class

public <X> ViewTarget<ImageView, X> buildImageViewTarget(
      @NonNull ImageView imageView, @NonNull Class<X> transcodeClass) {
    return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}

public class ImageViewTargetFactory {
  @NonNull
  @SuppressWarnings("unchecked")
  public <Z> ViewTarget<ImageView, Z> buildTarget(
      @NonNull ImageView view, @NonNull Class<Z> clazz) {
    if (Bitmap.class.equals(clazz)) {
      return (ViewTarget<ImageView, Z>) new BitmapImageViewTarget(view);
    } else if (Drawable.class.isAssignableFrom(clazz)) {
      return (ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view);
    } else {
      throw new IllegalArgumentException(
          "Unhandled class: " + clazz + ", try .as*(Class).transcode(ResourceTranscoder)");
    }
  }
}

入参为target的into方法中，有四个入参，分别为target，监听,配置信息,和线程池，其代码如下，
其中通过buildRequest创建一个请求

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()");
    }
    //创建request对象
    Request request = buildRequest(target, targetListener, options, callbackExecutor);

    Request previous = target.getRequest();
    if (request.isEquivalentTo(previous)
        && !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
      if (!Preconditions.checkNotNull(previous).isRunning()) {
        previous.begin();
      }
      return target;
    }
    //将target原先所关联的请求断开
    requestManager.clear(target);
    //并设置为新的请求，
    target.setRequest(request);
    //然后通过requestManager.track()进行一些列的加载和处理显示操作
    requestManager.track(target, request);

    return target;
}

requestManager.track

track方法代码如下

synchronized void track(@NonNull Target<?> target, @NonNull Request request) {
    targetTracker.track(target);
    requestTracker.runRequest(request);
}

//将请求保存起来
public void track(@NonNull Target<?> target) {
    targets.add(target);
}

//如果当前不是暂停状态则调用begin方法处理请求，如果是暂停状态则加入到pendingRequests集合中
public void runRequest(@NonNull Request request) {
    requests.add(request);
    if (!isPaused) {
      request.begin();
    } else {
      request.clear();
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        Log.v(TAG, "Paused, delaying request");
      }
      pendingRequests.add(request);
    }
}

SingleRequest.begin

而通过跟踪buildRequest方法，发现到最后是调用SingleRequest.obtain创建Request实例，也就是Request的实现类是SingleRequest，那么来看一下SingleRequest的begin方法

public void begin() {
    synchronized (requestLock) {
      assertNotCallingCallbacks();
      stateVerifier.throwIfRecycled();
      startTime = LogTime.getLogTime();
      ...
      status = Status.WAITING_FOR_SIZE;
      if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
        //将目标view的宽高传入onSizeReady
        onSizeReady(overrideWidth, overrideHeight);
      } else {
        target.getSize(this);
      }

      if ((status == Status.RUNNING || status == Status.WAITING_FOR_SIZE)
          && canNotifyStatusChanged()) {
        target.onLoadStarted(getPlaceholderDrawable());
      }
      if (IS_VERBOSE_LOGGABLE) {
        logV("finished run method in " + LogTime.getElapsedMillis(startTime));
      }
    }
}

通过上面代码可以看出begin中最关键的一行是调用onSizeReady方法，并传入目标view的宽高，onSizeReady代码如下

public void onSizeReady(int width, int height) {
    stateVerifier.throwIfRecycled();
    synchronized (requestLock) {
      ...
      if (status != Status.WAITING_FOR_SIZE) {
        return;
      }
      //修改status为running
      status = Status.RUNNING;

      float sizeMultiplier = requestOptions.getSizeMultiplier();
      this.width = maybeApplySizeMultiplier(width, sizeMultiplier);
      this.height = maybeApplySizeMultiplier(height, sizeMultiplier);

      //调用Engine.load对请求进行处理
      loadStatus =
          engine.load(
              glideContext,
              model,
              requestOptions.getSignature(),
              this.width,
              this.height,
              requestOptions.getResourceClass(),
              transcodeClass,
              priority,
              requestOptions.getDiskCacheStrategy(),
              requestOptions.getTransformations(),
              requestOptions.isTransformationRequired(),
              requestOptions.isScaleOnlyOrNoTransform(),
              requestOptions.getOptions(),
              requestOptions.isMemoryCacheable(),
              requestOptions.getUseUnlimitedSourceGeneratorsPool(),
              requestOptions.getUseAnimationPool(),
              requestOptions.getOnlyRetrieveFromCache(),
              this,
              callbackExecutor);

      if (status != Status.RUNNING) {
        loadStatus = null;
      }
    }
}

Engine.load

可以看到上面onSizeReady主要是调用了Engine.load()对请求进行处理,其代码如下，

public <R> LoadStatus load(
      GlideContext glideContext,
      Object model,
      Key signature,
      int width,
      int height,
      Class<?> resourceClass,
      Class<R> transcodeClass,
      Priority priority,
      DiskCacheStrategy diskCacheStrategy,
      Map<Class<?>, Transformation<?>> transformations,
      boolean isTransformationRequired,
      boolean isScaleOnlyOrNoTransform,
      Options options,
      boolean isMemoryCacheable,
      boolean useUnlimitedSourceExecutorPool,
      boolean useAnimationPool,
      boolean onlyRetrieveFromCache,
      ResourceCallback cb,
      Executor callbackExecutor) {
    long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;

    EngineKey key =
        keyFactory.buildKey(
            model,
            signature,
            width,
            height,
            transformations,
            resourceClass,
            transcodeClass,
            options);

    EngineResource<?> memoryResource;
    synchronized (this) {
      //获取缓存中的图片资源
      memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);

      if (memoryResource == null) {
        //缓存中没有则等待或新开一个job获取图片资源
        return waitForExistingOrStartNewJob(
            glideContext,
            model,
            signature,
            width,
            height,
            resourceClass,
            transcodeClass,
            priority,
            diskCacheStrategy,
            transformations,
            isTransformationRequired,
            isScaleOnlyOrNoTransform,
            options,
            isMemoryCacheable,
            useUnlimitedSourceExecutorPool,
            useAnimationPool,
            onlyRetrieveFromCache,
            cb,
            callbackExecutor,
            key,
            startTime);
      }
    }

    // Avoid calling back while holding the engine lock, doing so makes it easier for callers to
    // deadlock.
    cb.onResourceReady(
        memoryResource, DataSource.MEMORY_CACHE, /* isLoadedFromAlternateCacheKey= */ false);
    return null;
}

Engine.load中主要是先通过loadFromMemory获取缓存中的图片资源，取不到则调用waitForExistingOrStartNewJob

Engine.loadFromMemory

loadFromMemory代码如下

private EngineResource<?> loadFromMemory(
      EngineKey key, boolean isMemoryCacheable, long startTime) {

    //判断是否允许内存缓存
    if (!isMemoryCacheable) {
      return null;
    }
    //从ActiveResources中取
    EngineResource<?> active = loadFromActiveResources(key);
    if (active != null) {
      return active;
    }
    //从lruCache中取
    EngineResource<?> cached = loadFromCache(key);
    if (cached != null) {
      return cached;
    }

    return null;
}

loadFromActiveResources

loadFromActiveResources代码如下，其中ActiveResources维护了一个value为弱引用的HashMap<Key, ResourceWeakReference>, 调用其get方法获取图片资源，如果取到则调用acquire对对象的引用数量进行加一操作，内存缓存是通过计数散列算法来进行相应的操作的，如果对象的计数树为0，则说明暂无其他对象引用此资源，那么此资源可以被释放了

private EngineResource<?> loadFromActiveResources(Key key) {
    EngineResource<?> active = activeResources.get(key);
    if (active != null) {
      active.acquire();
    }
    return active;
}

private final ActiveResources activeResources;

final class ActiveResources {
    private final boolean isActiveResourceRetentionAllowed;
    private final Executor monitorClearedResourcesExecutor;
    @VisibleForTesting final Map<Key, ResourceWeakReference> activeEngineResources = new HashMap<>();
    private final ReferenceQueue<EngineResource<?>> resourceReferenceQueue = new ReferenceQueue<>();
    private ResourceListener listener;
    private volatile boolean isShutdown;
    @Nullable private volatile DequeuedResourceCallback cb;
    ...
    synchronized void activate(Key key, EngineResource<?> resource) {
        ResourceWeakReference toPut =
            new ResourceWeakReference(
                key, resource, resourceReferenceQueue, isActiveResourceRetentionAllowed);

        ResourceWeakReference removed = activeEngineResources.put(key, toPut);
        if (removed != null) {
          removed.reset();
        }
   }
   synchronized EngineResource<?> get(Key key) {
       ResourceWeakReference activeRef = activeEngineResources.get(key);
       if (activeRef == null) {
         return null;
       }

       EngineResource<?> active = activeRef.get();
       if (active == null) {
         cleanupActiveReference(activeRef);
       }
       return active;
   }
}
class EngineResource<Z> implements Resource<Z> {
    ...
    private int acquired;
    private boolean isRecycled;
    ...
    synchronized void acquire() {
        if (isRecycled) {
          throw new IllegalStateException("Cannot acquire a recycled resource");
        }
        ++acquired;
    }
}

loadFromCache

继续回到loadFromMemory，如果ActiveResources中没有取到，则调用loadFromCache尝试从lruCache中取，loadFromCache代码如下，从lruCache中取图片资源，如果取到则调用acquire对对象的引用数量进行加一操作，并调用activeResources.activate添加到activeResources中

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) {
    // 对于Lru的数据获取是通过删除的方式来获取
    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;
}

上面代码中的cache就是前面GlideBuilder.build中初始化的memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());

LruResourceCache

LruResourceCache继承了LruCache，并实现MemoryCache接口，LruCache内部利用了LinkedHashMap accessOrder 等于true时会对内容按照访问的先后顺序排序，会把最近访问的元素放到双链表的尾部这样一个特性实现的，代码如下

public class LruResourceCache extends LruCache<Key, Resource<?>> implements MemoryCache {
    ...
}

public class LruCache<T, Y> {
    private final Map<T, Entry<Y>> cache = new LinkedHashMap<>(100, 0.75f, true);
    private final long initialMaxSize;
    private long maxSize;
    private long currentSize;
    ...
    public synchronized Y remove(@NonNull T key) {
        Entry<Y> entry = cache.remove(key);
        if (entry == null) {
          return null;
        }
        currentSize -= entry.size;
        return entry.value;
    }
    ...
}
public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>{
    public LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) {
            super(initialCapacity, loadFactor);
            this.accessOrder = accessOrder;
    }
    ...
}

waitForExistingOrStartNewJob

那么回到Engine.load，loadFromMemory取不到, 则调用waitForExistingOrStartNewJob,代码如下

final class Jobs {
  private final Map<Key, EngineJob<?>> jobs = new HashMap<>();
  private final Map<Key, EngineJob<?>> onlyCacheJobs = new HashMap<>();
  ...
}
private <R> LoadStatus waitForExistingOrStartNewJob(...) {
    //先从jobs中取EngineJob
    EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
    if (current != null) {
      current.addCallback(cb, callbackExecutor);
      //取到则直接创建一个LoadStatus返回
      return new LoadStatus(cb, current);
    }

    //取不到则通过engineJobFactory.build创建一个EngineJob
    EngineJob<R> engineJob =
        engineJobFactory.build(
            key,
            isMemoryCacheable,
            useUnlimitedSourceExecutorPool,
            useAnimationPool,
            onlyRetrieveFromCache);

    DecodeJob<R> decodeJob =
        decodeJobFactory.build(
            glideContext,
            model,
            key,
            signature,
            width,
            height,
            resourceClass,
            transcodeClass,
            priority,
            diskCacheStrategy,
            transformations,
            isTransformationRequired,
            isScaleOnlyOrNoTransform,
            onlyRetrieveFromCache,
            options,
            engineJob);

    //将创建的engineJob加入到jobs
    jobs.put(key, engineJob);

    engineJob.addCallback(cb, callbackExecutor);
    //调用start开启线程获取图片
    engineJob.start(decodeJob);

    return new LoadStatus(cb, engineJob);
}

engineJob.start

上面最重要的就是engineJob.start这一行，开启线程获取图片，start方法代码如下

public synchronized void start(DecodeJob<R> decodeJob) {
    this.decodeJob = decodeJob;
    GlideExecutor executor =
        //判断是否需要磁盘缓存，是则使用磁盘线程池，否则使用内存缓存线程池
        decodeJob.willDecodeFromCache() ? diskCacheExecutor : getActiveSourceExecutor();
    //执行job
    executor.execute(decodeJob);
}

从GlideBuilder.build中可以找到diskCacheExecutor的初始化

diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();

public final class GlideExecutor implements ExecutorService {
    public static GlideExecutor newDiskCacheExecutor() {
        return newDiskCacheBuilder().build();
    }
    public static GlideExecutor.Builder newDiskCacheBuilder() {
        return new GlideExecutor.Builder(/*preventNetworkOperations=*/ true)
            .setThreadCount(DEFAULT_DISK_CACHE_EXECUTOR_THREADS)
            .setName(DEFAULT_DISK_CACHE_EXECUTOR_NAME);
    }
    GlideExecutor(ExecutorService delegate) {
        this.delegate = delegate;
    }
    public void execute(@NonNull Runnable command) {
        delegate.execute(command);
    }
    public static final class Builder {
        ...
        public GlideExecutor build() {
              if (TextUtils.isEmpty(name)) {
                throw new IllegalArgumentException(
                    "Name must be non-null and non-empty, but given: " + name);
              }
              ThreadPoolExecutor executor =
                  new ThreadPoolExecutor(
                      corePoolSize,
                      maximumPoolSize,
                      /*keepAliveTime=*/ threadTimeoutMillis,
                      TimeUnit.MILLISECONDS,
                      new PriorityBlockingQueue<Runnable>(),
                      new DefaultThreadFactory(name, uncaughtThrowableStrategy, preventNetworkOperations));

              if (threadTimeoutMillis != NO_THREAD_TIMEOUT) {
                executor.allowCoreThreadTimeOut(true);
              }

              return new GlideExecutor(executor);
          }
    }
}

不管是磁盘缓存还是内存最终都会调用DecodeJob(继承Runnable)的run，接着会调用runWrapped

class DecodeJob<R>
    implements DataFetcherGenerator.FetcherReadyCallback,
        Runnable, Comparable<DecodeJob<?>>, Poolable {

    public void run() {
        ...
        try {
          if (isCancelled) {
            notifyFailed();
            return;
          }

          runWrapped();
        } catch (
        ...
    }

    private void runWrapped() {
        switch (runReason) {
          case INITIALIZE:
            //调用getNextStage后返回Stage.RESOURCE_CACHE
            stage = getNextStage(Stage.INITIALIZE);
            currentGenerator = getNextGenerator();
            runGenerators();
            break;
          case SWITCH_TO_SOURCE_SERVICE:
            runGenerators();
            break;
          case DECODE_DATA:
            decodeFromRetrievedData();
            break;
          default:
            throw new IllegalStateException("Unrecognized run reason: " + runReason);
        }
    }
}

//getNextState中会根据磁盘缓存的策略判断来指定Stage值
private Stage getNextStage(Stage current) {
    switch (current) {
      case INITIALIZE:
        return diskCacheStrategy.decodeCachedResource()
            ? Stage.RESOURCE_CACHE
            : getNextStage(Stage.RESOURCE_CACHE);
      case RESOURCE_CACHE:
        return diskCacheStrategy.decodeCachedData()
            ? Stage.DATA_CACHE
            : getNextStage(Stage.DATA_CACHE);
      case DATA_CACHE:
        // Skip loading from source if the user opted to only retrieve the resource from cache.
        return onlyRetrieveFromCache ? Stage.FINISHED : Stage.SOURCE;
      case SOURCE:
      case FINISHED:
        return Stage.FINISHED;
      default:
        throw new IllegalArgumentException("Unrecognized stage: " + current);
    }
}

runReason在初始化DecodeJob的时候设置初始为INITIALIZE,所以会调用getNextGenerator，且getNextStage后stage为RESOURCE_CACHE，所以最终返回ResourceCacheGenerator

private DataFetcherGenerator getNextGenerator() {
    switch (stage) {
      case RESOURCE_CACHE:
        return new ResourceCacheGenerator(decodeHelper, this);
      case DATA_CACHE:
        return new DataCacheGenerator(decodeHelper, this);
      case SOURCE:
        return new SourceGenerator(decodeHelper, this);
      case FINISHED:
        return null;
      default:
        throw new IllegalStateException("Unrecognized stage: " + stage);
    }
}

runGenerators

DecodeJob.runWrapped最后会调用runGenerators

private void runGenerators() {
    ...
    while (!isCancelled
        && currentGenerator != null
        && !(isStarted = currentGenerator.startNext())) {
      stage = getNextStage(stage);
      currentGenerator = getNextGenerator();

      if (stage == Stage.SOURCE) {
        reschedule();
        return;
      }
    }
    ...
}

其中while中的currentGenerator就是上面几个状态对应的ResourceCacheGenerator，DataCacheGenerator，SourceGenerator；
前两个都是缓存的让我们来看一下SourceGenerator的startNext；

SourceGenerator.startNext

runGenerators中最关键的一步是调用了currentGenerator.startNext

public boolean startNext() {
    ...
    while (!started && hasNextModelLoader()) {
      loadData = helper.getLoadData().get(loadDataListIndex++);
      if (loadData != null
          && (helper.getDiskCacheStrategy().isDataCacheable(loadData.fetcher.getDataSource())
              || helper.hasLoadPath(loadData.fetcher.getDataClass()))) {
        started = true;
        startNextLoad(loadData);
      }
    }
    return started;
}

private void startNextLoad(final LoadData<?> toStart) {
    //这里只需要关注loadData.fetcher.loadData方法
    loadData.fetcher.loadData(
        helper.getPriority(),
        new DataCallback<Object>() {
          @Override
          public void onDataReady(@Nullable Object data) {
            if (isCurrentRequest(toStart)) {
              onDataReadyInternal(toStart, data);
            }
          }

          @Override
          public void onLoadFailed(@NonNull Exception e) {
            if (isCurrentRequest(toStart)) {
              onLoadFailedInternal(toStart, e);
            }
          }
        });
}

上面代码中helper.getLoadData代码如下

List<LoadData<?>> getLoadData() {
    if (!isLoadDataSet) {
      isLoadDataSet = true;
      loadData.clear();
      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;
}

其中buildLoadData是在HttpGlideUrlLoader中实现的

HttpGlideUrlLoader.buildLoadData

public LoadData<InputStream> buildLoadData(
      @NonNull GlideUrl model, int width, int height, @NonNull Options options) {
    // GlideUrls memoize parsed URLs so caching them saves a few object instantiations and time
    // spent parsing urls.
    GlideUrl url = model;
    if (modelCache != null) {
      url = modelCache.get(model, 0, 0);
      if (url == null) {
        modelCache.put(model, 0, 0, model);
        url = model;
      }
    }
    int timeout = options.get(TIMEOUT);
    return new LoadData<>(url, new HttpUrlFetcher(url, timeout));
}

而SourceGenerator.startNext的startNextLoad中，调用了loadData.fetcher.loadData方法，而从上面代码最后一行我们知道fetcher的实际类型就是HttpUrlFetcher，那么我们看看其loadData方法的实现

HttpUrlFetcher.loadData

public void loadData(
      @NonNull Priority priority, @NonNull DataCallback<? super InputStream> callback) {
    long startTime = LogTime.getLogTime();
    try {
      InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
      callback.onDataReady(result);
    } catch (IOException e) {
      if (Log.isLoggable(TAG, Log.DEBUG)) {
        Log.d(TAG, "Failed to load data for url", e);
      }
      callback.onLoadFailed(e);
    } finally {
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        Log.v(TAG, "Finished http url fetcher fetch in " + LogTime.getElapsedMillis(startTime));
      }
    }
}

可以看到其中调用了loadDataWithRedirects，代码如下：

 private InputStream loadDataWithRedirects(
      URL url, int redirects, URL lastUrl, Map<String, String> headers) throws HttpException {
    ...

    urlConnection = buildAndConfigureConnection(url, headers);

    try {
      // Connect explicitly to avoid errors in decoders if connection fails.
      urlConnection.connect();
      // Set the stream so that it's closed in cleanup to avoid resource leaks. See #2352.
      stream = urlConnection.getInputStream();
    } catch (IOException e) {
      throw new HttpException(
          "Failed to connect or obtain data", getHttpStatusCodeOrInvalid(urlConnection), e);
    }

    if (isCancelled) {
      return null;
    }

    final int statusCode = getHttpStatusCodeOrInvalid(urlConnection);
    ...
}

上面代码中我们看到了熟悉的urlConnection，那么看一下buildAndConfigureConnection方法的实现吧

private HttpURLConnection buildAndConfigureConnection(URL url, Map<String, String> headers)
      throws HttpException {
    HttpURLConnection urlConnection;
    try {
      urlConnection = connectionFactory.build(url);
    } catch (IOException e) {
      throw new HttpException("URL.openConnection threw", /*statusCode=*/ 0, e);
    }
    for (Map.Entry<String, String> headerEntry : headers.entrySet()) {
      urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue());
    }
    urlConnection.setConnectTimeout(timeout);
    urlConnection.setReadTimeout(timeout);
    urlConnection.setUseCaches(false);
    urlConnection.setDoInput(true);
    // Stop the urlConnection instance of HttpUrlConnection from following redirects so that
    // redirects will be handled by recursive calls to this method, loadDataWithRedirects.
    urlConnection.setInstanceFollowRedirects(false);
    return urlConnection;
}

到此我们终于看到了网络请求相关的代码，原来Glide使用的HttpURLConnection进行网络请求

SourceGenerator.onDataReadyInternal

而从上面SourceGenerator.startNextNext中的loadData.fetcher.loadData的入参DataCallback的onDataReady我们知道，如果请求成功，会将资源通过onDataReady传递回去，其中调用了onDataReadyInternal，代码如下

void onDataReadyInternal(LoadData<?> loadData, Object data) {
    //获取磁盘加载策略
    DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy();
    //判断是否缓存原始数据
    if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) {
      dataToCache = data;
      // We might be being called back on someone else's thread. Before doing anything, we should
      // reschedule to get back onto Glide's thread.
      cb.reschedule();
    } else {
      //cb为DecodeJob
      cb.onDataFetcherReady(
          loadData.sourceKey,
          data,
          loadData.fetcher,
          loadData.fetcher.getDataSource(),
          originalKey);
    }
}

上面的cb实际为DecodeJob，那么来看一下DecodeJob.onDataFetcherReady

public void onDataFetcherReady(
      Key sourceKey, Object data, DataFetcher<?> fetcher, DataSource dataSource, Key attemptedKey) {
    this.currentSourceKey = sourceKey;
    this.currentData = data;
    this.currentFetcher = fetcher;
    this.currentDataSource = dataSource;
    this.currentAttemptingKey = attemptedKey;
    this.isLoadingFromAlternateCacheKey = sourceKey != decodeHelper.getCacheKeys().get(0);

    if (Thread.currentThread() != currentThread) {
      runReason = RunReason.DECODE_DATA;
      callback.reschedule(this);
    } else {
      GlideTrace.beginSection("DecodeJob.decodeFromRetrievedData");
      try {
        decodeFromRetrievedData();
      } finally {
        GlideTrace.endSection();
      }
    }
}

上面代码中又调用了decodeFromRetrievedData，代码如下

private void decodeFromRetrievedData() {
    if (Log.isLoggable(TAG, Log.VERBOSE)) {
      logWithTimeAndKey(
          "Retrieved data",
          startFetchTime,
          "data: "
              + currentData
              + ", cache key: "
              + currentSourceKey
              + ", fetcher: "
              + currentFetcher);
    }
    Resource<R> resource = null;
    try {
      //解析图片
      resource = decodeFromData(currentFetcher, currentData, currentDataSource);
    } catch (GlideException e) {
      e.setLoggingDetails(currentAttemptingKey, currentDataSource);
      throwables.add(e);
    }
    if (resource != null) {
      //通知图片获取完毕
      notifyEncodeAndRelease(resource, currentDataSource, isLoadingFromAlternateCacheKey);
    } else {
      runGenerators();
    }
}

notifyEncodeAndRelease代码如下

private void notifyEncodeAndRelease(
      Resource<R> resource, DataSource dataSource, boolean isLoadedFromAlternateCacheKey) {
    if (resource instanceof Initializable) {
      ((Initializable) resource).initialize();
    }

    Resource<R> result = resource;
    LockedResource<R> lockedResource = null;
    if (deferredEncodeManager.hasResourceToEncode()) {
      lockedResource = LockedResource.obtain(resource);
      result = lockedResource;
    }

    notifyComplete(result, dataSource, isLoadedFromAlternateCacheKey);

    stage = Stage.ENCODE;
    try {
      if (deferredEncodeManager.hasResourceToEncode()) {
        deferredEncodeManager.encode(diskCacheProvider, options);
      }
    } finally {
      if (lockedResource != null) {
        lockedResource.unlock();
      }
    }
    // Call onEncodeComplete outside the finally block so that it's not called if the encode process
    // throws.
    onEncodeComplete();
}

探索Android开源框架 - 4. Glide使用及源码解析

使用

1. 添加依赖

2. 基础使用

3. 进阶操作

源码解析

1. with

获取Glide实例

RequestManagerRetriever.get

2. load

asDrawable()

RequestBuilder.load

3. into

requestManager.track

SingleRequest.begin

Engine.load

Engine.loadFromMemory

loadFromActiveResources

loadFromCache

LruResourceCache

waitForExistingOrStartNewJob

engineJob.start

runGenerators

SourceGenerator.startNext

HttpGlideUrlLoader.buildLoadData

HttpUrlFetcher.loadData

SourceGenerator.onDataReadyInternal

参考

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