Glide生命周期管理

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

private RequestManager getApplicationManager(Context context) {
        ......
        applicationManager = factory.build(glide, new ApplicationLifecycle(), new EmptyRequestManagerTreeNode());//------主要这句
        ......

        return applicationManager;
    }

class ApplicationLifecycle implements Lifecycle {
  @Override
  public void addListener(LifecycleListener listener) {
    listener.onStart();
  }

  @Override
  public void removeListener(LifecycleListener listener) {
    // Do nothing.
  }
}

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

  @Override
  public void addListener(LifecycleListener listener) {
    lifecycleListeners.add(listener);

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

if (Util.isOnBackgroundThread()) {
            mainHandler.post(addSelfToLifecycle);
        } else {
            lifecycle.addListener(this);//这样就算是这是开启生命周期管理
        }