Glide的源码分析(一) Activity的生命周期与图片加载的关系

从这段代码入手分析Glide

    Glide.with(context)
       .load(url)
       .placeholder(R.drawable.loading)
       .error(R.drawable.avatar)
       .listener(new RequestListener<String, GlideDrawable>() {
            @Override
            public boolean onException(Exception e, String model, Target<GlideDrawable> target, boolean isFirstResource) {
                return false;
            }

            @Override
            public boolean onResourceReady(GlideDrawable resource, String model, Target<GlideDrawable> target, boolean  
                 isFromMemoryCache, boolean isFirstResource) {
                 LogUtil.logV("loadPhotoDebug", "loadAvatar onResourceReady url = " + url);
                 if (isSimpleImage(tagView.getTag(), url)) {
                     return false;
                 }
                 mImageView.setImageResource(R.drawable.loading);
                 return true;
           }
       })
      .bitmapTransform(new CropCircleTransformation(context))
      .into(mImageView);

1.Glide.with(context)分析

Glide.java:

    public static RequestManager with(Context context) {
        RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(context);
    }

RequestManagerRetriever.java:

    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);
    }
    
    public RequestManager get(FragmentActivity activity) {
        if (Util.isOnBackgroundThread()) {
            return get(activity.getApplicationContext());
        } else {
            assertNotDestroyed(activity);
            FragmentManager fm = activity.getSupportFragmentManager();
            return supportFragmentGet(activity, fm);
        }
    }

    public RequestManager get(Fragment fragment) {
        if (fragment.getActivity() == null) {
            throw new IllegalArgumentException("You cannot start a load on a fragment before it is attached");
        }
        if (Util.isOnBackgroundThread()) {
            return get(fragment.getActivity().getApplicationContext());
        } else {
            FragmentManager fm = fragment.getChildFragmentManager();
            return supportFragmentGet(fragment.getActivity(), fm);
        }
    }

从这段代码可以看出无论Glide.with传入的Context是Fragment还是Activity或者干脆传入Framgent或FragemtnActivity,都会调用supportFragmentGet这个方法

RequestManagerRetriever.java:

    RequestManager supportFragmentGet(Context context, FragmentManager fm) {
        SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
        RequestManager requestManager = current.getRequestManager();
        if (requestManager == null) {
            requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
            current.setRequestManager(requestManager);
        }
        return requestManager;
    }
    
    SupportRequestManagerFragment getSupportRequestManagerFragment(final FragmentManager fm) {
        SupportRequestManagerFragment current = (SupportRequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
        if (current == null) {
            current = pendingSupportRequestManagerFragments.get(fm);
            if (current == null) {
                current = new SupportRequestManagerFragment();
                pendingSupportRequestManagerFragments.put(fm, current);
                fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
                handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
            }
        }
        return current;
    }

而supportFragmentGet这个方法生成两个对象：
1.SupportRequestManagerFragment对象， 并把它加到FragmentManager上；
2.RequestManager对象
这两个对象拥有共同的对象LifeStyle对象，当Android系统调用SupportRequestManagerFragment的生命周期，RequestManger的生命周期随之被调用来处理Request列表，
将Fragment的生命周期与RequestManger的生命周期联系起来:

SupportRequestManagerFragment.java:

    @Override
    public void onStart() {
        super.onStart();
        lifecycle.onStart();
    }

    @Override
    public void onStop() {
        super.onStop();
        lifecycle.onStop();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        lifecycle.onDestroy();
    }

RequestManager.java

public class RequestManager implements LifecycleListener {
    RequestManager(Context context, final Lifecycle lifecycle, RequestManagerTreeNode treeNode,
            RequestTracker requestTracker, ConnectivityMonitorFactory factory) {
        ... ...
        this.lifecycle = lifecycle;
        ConnectivityMonitor connectivityMonitor = factory.build(context,
                new RequestManagerConnectivityListener(requestTracker));
        ... ... 
        if (Util.isOnBackgroundThread()) {
            new Handler(Looper.getMainLooper()).post(new Runnable() {
                @Override
                public void run() {
                    lifecycle.addListener(RequestManager.this);
                }
            });
        } else {
            lifecycle.addListener(this);
        }
        lifecycle.addListener(connectivityMonitor);
    }
    
    
    @Override
    public void onStart() {
        // onStart might not be called because this object may be created after the fragment/activity's onStart method.
        resumeRequests();
    }

    /**
     * Lifecycle callback that unregisters for connectivity events (if the android.permission.ACCESS_NETWORK_STATE
     * permission is present) and pauses in progress loads.
     */
    @Override
    public void onStop() {
        pauseRequests();
    }

    /**
     * Lifecycle callback that cancels all in progress requests and clears and recycles resources for all completed
     * requests.
     */
    @Override
    public void onDestroy() {
        requestTracker.clearRequests();
    }

如果传入的是Applicaton Context,

     private RequestManager getApplicationManager(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.
                    applicationManager = new RequestManager(context.getApplicationContext(),
                            new ApplicationLifecycle(), new EmptyRequestManagerTreeNode());
                }
            }
        }

        return applicationManager;
    }

会得到一个单例的RequestManager对象，RequestManager绑定的生命周期并不会调用onStop,onDestroy,

ApplicationLifecycle.java:

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

总结：Glide.with(Context)将Activity的生命周期与RequestManager针对的request的处理联系起来，

 传入ApplicationContext，会得到一个单例的RequestManager对象;
 传入Activity Context,会得到一个属于一个Activity的RequestManager对象;