Android知识Android开发经验谈

从源码角度深入理解Glide（上）

2019-02-20  本文已影响15人  maoqitian
glide_logo.png

谈到Glide，从英文字面意思有滑行、滑动的意思；而Android从开发的角度我们知道它是一款图片加载框架，这里引用官方文档的一句话“Glide是一个快速高效的Android图片加载库，注重于平滑的滚动”，从官方文档介绍我们了解到用Glide框架来加载图片是快速并且高效的，接下来就来通过简单使用Glide和源码理解两个方面看看Glide是否是快速和高效（文中代码基于Glide 4.8版本）。

Glide简单使用

显示占位图.gif glide_transformation.gif glide_notification.gif

Glide还有其他的一些使用方法，这里就不继续展开了，有兴趣的可以自行继续研究。

Glide源码解析

Glide加载图片到ImageView基本流程图

Glide基本请求流程图.jpg

Glide加载图片到ImageView源码分析

Glide.with(Context).load(IMAGE_URL).into(mImageView);

with方法

/** Glide类的with()方法*/
@NonNull
  public static RequestManager with(@NonNull Context context) {
    return getRetriever(context).get(context);
  }

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

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

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

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

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

 /** Glide类的getRetriever()方法*/
 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();
  }

/** RequestManagerRetriever类的get()方法*/
 @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)) {
      if (context instanceof FragmentActivity) {
        return get((FragmentActivity) context);
      } else if (context instanceof Activity) {
        return get((Activity) context);
      } else if (context instanceof ContextWrapper) {
        return get(((ContextWrapper) context).getBaseContext());
      }
    }
    return getApplicationManager(context);
  }

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

  @NonNull
  public RequestManager get(@NonNull Fragment fragment) {
    Preconditions.checkNotNull(fragment.getActivity(),
          "You cannot start a load on a fragment before it is attached or after it is destroyed");
    if (Util.isOnBackgroundThread()) {
      return get(fragment.getActivity().getApplicationContext());
    } else {
      FragmentManager fm = fragment.getChildFragmentManager();
      return supportFragmentGet(fragment.getActivity(), fm, fragment, fragment.isVisible());
    }
  }

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

  @SuppressWarnings("deprecation")
  @NonNull
  public RequestManager get(@NonNull View view) {
    if (Util.isOnBackgroundThread()) {
      return get(view.getContext().getApplicationContext());
    }
    Preconditions.checkNotNull(view);
    Preconditions.checkNotNull(view.getContext(),
        "Unable to obtain a request manager for a view without a Context");
    Activity activity = findActivity(view.getContext());
    // The view might be somewhere else, like a service.
    if (activity == null) {
      return get(view.getContext().getApplicationContext());
    }

    // Support Fragments.
    // Although the user might have non-support Fragments attached to FragmentActivity, searching
    // for non-support Fragments is so expensive pre O and that should be rare enough that we
    // prefer to just fall back to the Activity directly.
    if (activity instanceof FragmentActivity) {
      Fragment fragment = findSupportFragment(view, (FragmentActivity) activity);
      return fragment != null ? get(fragment) : get(activity);
    }

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

/** RequestManagerRetriever类的getApplicationManager()方法*/
  @NonNull
  private RequestManager getApplicationManager(@NonNull Context context) {
    // Either an application context or we're on a background thread.
    if (applicationManager == null) {
      synchronized (this) {
        if (applicationManager == null) {
          // Normally pause/resume is taken care of by the fragment we add to the fragment or
          // activity. However, in this case since the manager attached to the application will not
          // receive lifecycle events, we must force the manager to start resumed using
          // ApplicationLifecycle.

          // TODO(b/27524013): Factor out this Glide.get() call.
          Glide glide = Glide.get(context.getApplicationContext());
          applicationManager =
              factory.build(
                  glide,
                  new ApplicationLifecycle(),
                  new EmptyRequestManagerTreeNode(),
                  context.getApplicationContext());
        }
      }
    }
    return applicationManager;
  }

/** RequestManagerRetriever类的fragmentGet()方法*/
  @SuppressWarnings({"deprecation", "DeprecatedIsStillUsed"})
  @Deprecated
  @NonNull
  private RequestManager fragmentGet(@NonNull Context context,
      @NonNull android.app.FragmentManager fm,
      @Nullable android.app.Fragment parentHint,
      boolean isParentVisible) {
    RequestManagerFragment current = getRequestManagerFragment(fm, parentHint, isParentVisible);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      current.setRequestManager(requestManager);
    }
    return requestManager;
  }
  
  /** RequestManagerRetriever类的getRequestManagerFragment()方法*/
  @SuppressWarnings("deprecation")
  @NonNull
  private RequestManagerFragment getRequestManagerFragment(
      @NonNull final android.app.FragmentManager fm,
      @Nullable android.app.Fragment parentHint,
      boolean isParentVisible) {
    RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
    if (current == null) {
      current = pendingRequestManagerFragments.get(fm);
      if (current == null) {
        current = new RequestManagerFragment();
        current.setParentFragmentHint(parentHint);
        if (isParentVisible) {
          current.getGlideLifecycle().onStart();
        }
        pendingRequestManagerFragments.put(fm, current);
        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
        handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
      }
    }
    return current;
  }

load方法

/** RequestManager 类的as()方法*/
 @NonNull
  @CheckResult
  public <ResourceType> RequestBuilder<ResourceType> as(
      @NonNull Class<ResourceType> resourceClass) {
    return new RequestBuilder<>(glide, this, resourceClass, context);
  }
/** RequestManager 类的as()方法*/
 @NonNull
  @CheckResult
  public RequestBuilder<Drawable> asDrawable() {
    return as(Drawable.class);
  }
/** RequestManager 类的部分load()方法*/
 @NonNull
  @CheckResult
  @Override
  public RequestBuilder<Drawable> load(@Nullable Bitmap bitmap) {
    return asDrawable().load(bitmap);
  }
  @NonNull
  @CheckResult
  @Override
  public RequestBuilder<Drawable> load(@Nullable Drawable drawable) {
    return asDrawable().load(drawable);
  }

  @NonNull
  @CheckResult
  @Override
  public RequestBuilder<Drawable> load(@Nullable String string) {
    return asDrawable().load(string);
  }
  //省略其他参数类型 load() 方法
 .......

/** RequestBuilder 类的load()方法*/
 @NonNull
  @CheckResult
  @SuppressWarnings("unchecked")
  @Override
  public RequestBuilder<TranscodeType> load(@Nullable Object model) {
    return loadGeneric(model);
  }
/** RequestBuilder对象 类的loadGeneric()方法*/
  @NonNull
  private RequestBuilder<TranscodeType> loadGeneric(@Nullable Object model) {
    this.model = model;
    isModelSet = true;
    return this;
  }

/** RequestBuilder 类的apply方法*/
 @NonNull
  @CheckResult
  public RequestBuilder<TranscodeType> apply(@NonNull RequestOptions requestOptions) {
    Preconditions.checkNotNull(requestOptions);
    this.requestOptions = getMutableOptions().apply(requestOptions);
    return this;
  }
 
  @SuppressWarnings("ReferenceEquality")
  @NonNull
  protected RequestOptions getMutableOptions() {
    return defaultRequestOptions == this.requestOptions
        ? this.requestOptions.clone() : this.requestOptions;
  }
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