Glide源码分析

一、现状

以下为一次Glide图片加载典型用法，会将所需相关配置写入 requestOptions 对象，通过 setDefaultRequestOptions 方法写入自定义配置。

                RequestOptions requestOptions =
                        RequestOptions.skipMemoryCacheOf(true).diskCacheStrategy(DiskCacheStrategy.NONE).dontAnimate()
                                .dontTransform();
                if (circleImg) {
                    requestOptions = requestOptions.transform(new CircleCrop());
                }
                if (placeHolder > 0) {
                    requestOptions = requestOptions.placeholder(placeHolder);
                }
                if (errorHolder > 0) {
                    requestOptions = requestOptions.error(errorHolder);
                }
                if (roundRadius > 0f) {
                    requestOptions = requestOptions.transform(new CenterCrop(),
                            new RoundedCorners(ScreenUtil.dp2px(context, roundRadius)));
                }

								Glide.with(context)
                            .setDefaultRequestOptions(requestOptions)
                            .load(uri)
                            .addListener(new RequestListener<Drawable>() {})
                            .into(imageView);

二、存在问题

当使用Glide进行图片加载时，若没有调用过 setDefaultRequestOptions 进行配置，可能存在将其他地方配置加载过来的情况，造成错乱。

三、原因分析

根据方法定义，初步判定是由于 setDefaultRequestOptions 存在持久化问题，在设置过一次后将会在后续操作中持续生效，直至下一次重新调用。

四、源码分析

4.1 Glide.with(context)

初始化入口方法，返回值 RequestManager

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

Glide#getRetriever 返回值 RequestManagerRetriever

@NonNull
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();
}

Glide.get 单例方法返回值 Glide

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

  return glide;
}

小结

Glide (singleInstance) -> RequestManagerRetriever -> RequestManager

4.2 Glide 初始化

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

  private static void initializeGlide(@NonNull Context context, @NonNull GlideBuilder builder) {
    Context applicationContext = context.getApplicationContext();

    // ..........此处省略部分代码............
    
    RequestManagerRetriever.RequestManagerFactory factory =
        annotationGeneratedModule != null
            ? annotationGeneratedModule.getRequestManagerFactory() : null;
    builder.setRequestManagerFactory(factory);
 
    // ..........此处省略部分代码............
    
    Glide glide = builder.build(applicationContext);

    // ..........此处省略部分代码............

    Glide.glide = glide;
  }

4.3 GlideBuilder 初始化

public final class GlideBuilder {
  
  private RequestOptions defaultRequestOptions = new RequestOptions();

  @NonNull
  public GlideBuilder setDefaultRequestOptions(@Nullable RequestOptions requestOptions) {
    this.defaultRequestOptions = requestOptions;
    return this;
  }
  
  Glide build(@NonNull Context context) {

  	// ..........此处省略部分代码............
  
    // 此处 RequestManagerRetriever 初始化
    RequestManagerRetriever requestManagerRetriever =
        new RequestManagerRetriever(requestManagerFactory);

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

小结

Glide 通过 GlideBuilder 进行初始化，并且在初始化时会为 RequestOptions 进行赋值，而赋值的 RequestOptions 对象在 GlideBuilder中通过无参构造被初始化，可判定该对象为初始默认配置。

RequestManagerRetriever 通过 GlideBuilder 进行初始化，并且赋值给Glide。

4.4 RequestManagerRetriever

Glide.get(context).getRequestManagerRetriever()

public class Glide implements ComponentCallbacks2 {
  private final RequestManagerRetriever requestManagerRetriever;
  
  /**
   * Internal method.
   */
  @NonNull
  public RequestManagerRetriever getRequestManagerRetriever() {
    return requestManagerRetriever;
  }
}

4.5 RequestManager

RequestManagerRetriever#get(Context)

@NonNull
public RequestManager get(@NonNull Context context) {
  if (context == null) {
    throw new IllegalArgumentException("You cannot start a load on a null Context");
  } else if (Util.isOnMainThread() && !(context instanceof Application)) {
    // 通过Activity添加Fragment 获取lifecycler 并且初始化 RequestManager
    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());
    }
  }
	
  // 初始化不含 lifecycler 的 RequestManager 单例
  return getApplicationManager(context);
}

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

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
private static void assertNotDestroyed(@NonNull Activity activity) {
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1 && activity.isDestroyed()) {
    throw new IllegalArgumentException("You cannot start a load for a destroyed activity");
  }
}

RequestManagerRetriever#getSupportRequestManagerFragment

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

小结

在Activity下，则创建Fragment，并使用Fragment创建的RequestManager，每个Activity存在且仅存在一个实例。
后台线程及非ActivityContext，使用统一的RequestManager公用实例。

意义

获取Lifecycle

4.6 初始化RequestManager

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

    return requestManager;
}

// Our usage is safe here.
@SuppressWarnings("PMD.ConstructorCallsOverridableMethod")
RequestManager(
    Glide glide,
    Lifecycle lifecycle,
    RequestManagerTreeNode treeNode,
    RequestTracker requestTracker,
    ConnectivityMonitorFactory factory,
    Context context) {
  
  // ..........此处省略部分代码............
  
  setRequestOptions(glide.getGlideContext().getDefaultRequestOptions());

  glide.registerRequestManager(this);
}

  protected synchronized void setRequestOptions(@NonNull RequestOptions toSet) {
    requestOptions = toSet.clone().autoClone();
  }

关键代码：setRequestOptions(glide.getGlideContext().getDefaultRequestOptions());

public final class GlideBuilder {
  private RequestOptions defaultRequestOptions = new RequestOptions();
  
    @NonNull
  Glide build(@NonNull Context context) {
        return new Glide(
     		...
        defaultRequestOptions.lock(),
   			...);
  }
}

小结

RequestManager初始化时，会将Glide中的初始RequestOptions进行克隆，并赋值给RequestManager。

4.7 RequestBuilder

由上述可知，Glide的结构关系如下，Glide -> RequestManagerRetriever -> RequestManager

其中Glide、RequestManagerRetriever为全局单例

RequestManager为局部单例

而实际完成一次图片加载流程最终则需要用到RequestBuilder，以 load(String)为例：

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

  protected RequestBuilder(
      @NonNull Glide glide,
      RequestManager requestManager,
      Class<TranscodeType> transcodeClass,
      Context context) {
    this.glide = glide;
    this.requestManager = requestManager;
    this.transcodeClass = transcodeClass;
    this.context = context;
    this.transitionOptions = requestManager.getDefaultTransitionOptions(transcodeClass);
    this.glideContext = glide.getGlideContext();

    initRequestListeners(requestManager.getDefaultRequestListeners());
    
    // 从requestManager继承requestOptions
    apply(requestManager.getDefaultRequestOptions());
  }

public T apply(@NonNull BaseRequestOptions<?> o) {
  	if (isAutoCloneEnabled) {
    	return clone().apply(o);
  	}
    BaseRequestOptions<?> other = o;

    if (isSet(other.fields, SIZE_MULTIPLIER)) {
      sizeMultiplier = other.sizeMultiplier;
    }
    if (isSet(other.fields, USE_UNLIMITED_SOURCE_GENERATORS_POOL)) {
      useUnlimitedSourceGeneratorsPool = other.useUnlimitedSourceGeneratorsPool;
    }
    ...
    fields |= other.fields;
    options.putAll(other.options);

    return selfOrThrowIfLocked();
  }

// RequestBuilder 继承自BaseRequestOptions
public class RequestBuilder<TranscodeType> extends BaseRequestOptions<RequestBuilder<TranscodeType>>
    implements Cloneable{}

小结

每一次请求会新建一个 RequestBuilder
RequestBuilder在初始化时使用apply() 从 RequestManager读取RequestOptions配置，且不会改变母体值。
RequestBuilder 继承自 BaseRequestOptions

五、结论

通过Activity Context 发起 Glide 事件，且当前处于主线程时，使用 setDefaultRequestOptions 会在当前Activity长期生效，直至下次重新赋值
通过非Activity Context发起或者当前处于子线程时，使用setDefaultRequestOptions会在全局长期生效，直至下次重新赋值
通过apply(BaseRequestOptions)设置，仅对当前本次加载生效
如果同时设置setDefaultRequestOptions 和 apply(BaseRequestOptions)，先生效前者，然后在此基础上生效后者的改动项