Glide源码解析之山清水秀疑无路（一）

本篇主要由以下内容构成：
1、框架结构简介
2、按照glide源码使用的时序图进行深入简述的方式讲解
3、核心类和核心模块总结
ps:本人博客写的太少，逻辑有时会走火入魔，希望你看到我的文章，可以理清自己的思路，哈哈，开玩笑。闲话少说，我们来开车，希望老司机来飙车，本篇主要记录自己学习的内容，如果能帮助其他的司机更是好极了。

废话太多，我们开车。

框架结构

好了：我这里项目用的是glie-3.7.0的源码，虽然每个源码，有点出入，但是结构上还是没有什么区别的。
它分为：加载策略： load包>data>
主要有：HttpUrlFetcher 网络加载
LocalUriFetcher 本地加载
MediaStoreThumbFetcher 媒体加载童鞋们可以自己对着看一下

缓存策略： engine>cache
里面有：MemoryCache DiskCache 这里先不说这些
转发策略占和上面的放到下一篇再说。

2.好了我们来根据常用的代码来进一步分析：

Glide.with(mApplication).load(url).into(target);

我们主要来分析一下常用的功能: 先从with下手，`public static RequestManager with(Context context) {RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(context);}/*** Begin a load with Glide that will be tied to the given {@link android.app.Activity}'s lifecycle and that uses the* given {@link Activity}'s default options.** @param activity The activity to use.* @return A RequestManager for the given activity that can be used to start a load.*/public static RequestManager with(Activity activity) {RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(activity);}/*** Begin a load with Glide that will tied to the give {@link android.support.v4.app.FragmentActivity}'s lifecycle* and that uses the given {@link android.support.v4.app.FragmentActivity}'s default options.** @param activity The activity to use.* @return A RequestManager for the given FragmentActivity that can be used to start a load.*/

//我们主要看这个代码
public static RequestManager with(FragmentActivity activity) { RequestManagerRetriever retriever = RequestManagerRetriever.get(); return retriever.get(activity);}

/*** Begin a load with Glide that will be tied to the given {@link android.app.Fragment}'s lifecycle and that uses* the given {@link android.app.Fragment}'s default options.** @param fragment The fragment to use.* @return A RequestManager for the given Fragment that can be used to start a load.*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public static RequestManager with(android.app.Fragment fragment) {RequestManagerRetriever retriever = RequestManagerRetriever.get();return retriever.get(fragment);

我们看到有很多重载方法，glide已经给你考虑非常周全了，我们只看这个重载方法

public static RequestManager with(FragmentActivity activity) { RequestManagerRetriever retriever = RequestManagerRetriever.get(); return retriever.get(activity);}

ok 我们点入 retriever.get(activity),进入  RequestManagerRetriever 这个类，

好了我们接着往下走：

//调用这个方法public RequestManager get(Context context) {if (context == null) {throw new IllegalArgumentException("You cannot start a load on a null Context");//判断是否在主线程} 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);}

我们接着看，supportFragmentGet(fragment.getActivity(), fm);做了什么诡秘的操作：

RequestManager supportFragmentGet(Context context, FragmentManager fm) {//OK 瞪着我们大眼和记住这个类  SupportRequestManagerFragment 这个就是一个空的FragmentSupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);RequestManager requestManager = current.getRequestManager();if (requestManager == null) {requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());current.setRequestManager(requestManager);}return requestManager;}

我们看到上面的代码，取出一个 SupportRequestManagerFragment 我们进入代码看看它是什么，还都有什么：

//这个一个fragment
public class SupportRequestManagerFragment extends Fragment {//还要记住这个成员变量 它是观察者private RequestManager requestManager;//记住这个成员变量 ActivityFragmentLifecycle lifecycle  它是一个被观察者，它接管了fragemnt//的生命周期private final ActivityFragmentLifecycle lifecycle;private final RequestManagerTreeNode requestManagerTreeNode =new SupportFragmentRequestManagerTreeNode();private final HashSet<SupportRequestManagerFragment> childRequestManagerFragments =new HashSet<SupportRequestManagerFragment>();private SupportRequestManagerFragment rootRequestManagerFragment;public SupportRequestManagerFragment() {this(new ActivityFragmentLifecycle());}// For testing only.@SuppressLint("ValidFragment")public SupportRequestManagerFragment(ActivityFragmentLifecycle lifecycle) {this.lifecycle = lifecycle;}/*** Sets the current {@link com.bumptech.glide.RequestManager}.** @param requestManager The manager to set.*/public void setRequestManager(RequestManager requestManager) {this.requestManager = requestManager;}ActivityFragmentLifecycle getLifecycle() {return lifecycle;}/*** Returns the current {@link com.bumptech.glide.RequestManager} or null if none is set.*/public RequestManager getRequestManager() {return requestManager;}/*** Returns the {@link RequestManagerTreeNode} that provides tree traversal methods relative to the associated* {@link RequestManager}.*/public RequestManagerTreeNode getRequestManagerTreeNode() {return requestManagerTreeNode;}private void addChildRequestManagerFragment(SupportRequestManagerFragment child) {childRequestManagerFragments.add(child);}private void removeChildRequestManagerFragment(SupportRequestManagerFragment child) {childRequestManagerFragments.remove(child);}
}

好的，先只要记住我注释的几个类，待会一一揭开他们的面目，我们来看看getSupportRequestManagerFragment(final FragmentManager fm)这个方法都做了什么？

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);//看到这里是不是知道，我们上面创造的SupportRequestManagerFragment如何当前页面绑定的就是在这里开始绑定的,通过添加事务的方法。fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();}}return current;}

我们再会到supportFragmentGet(Context context, FragmentManager fm)这个方法；

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;}

我们来在说说 SupportRequestManagerFragment 里面的生命周期方法是如何被 ActivityFragmentLifecycle lifecycle;接管的

@Overridepublic void onStart() {super.onStart();
//看见没有   ActivityFragmentLifecycle    lifecyclelifecycle.onStart();}@Overridepublic void onStop() {super.onStop();lifecycle.onStop();}@Overridepublic void onDestroy() {super.onDestroy();lifecycle.onDestroy();}

那你肯定要问了 ActivityFragmentLifecycle lifecycle到底是个什么玩意呢？
我们来看看：

 //实现了 Lifecycle 接口， 然后又有 addListener(LifecycleListener listener)方法，一看就像观察者套路
class ActivityFragmentLifecycle implements Lifecycle {private final Set<LifecycleListener> lifecycleListeners =Collections.newSetFromMap(new WeakHashMap<LifecycleListener, Boolean>());private boolean isStarted;private boolean isDestroyed;/*** Adds the given listener to the list of listeners to be notified on each lifecycle event.** <p>*     The latest lifecycle event will be called on the given listener synchronously in this method. If the*     activity or fragment is stopped, {@link LifecycleListener#onStop()}} will be called, and same for onStart and*     onDestroy.* </p>** <p>*     Note - {@link com.bumptech.glide.manager.LifecycleListener}s that are added more than once will have their*     lifecycle methods called more than once. It is the caller's responsibility to avoid adding listeners*     multiple times.* </p>*/@Overridepublic void addListener(LifecycleListener listener) {lifecycleListeners.add(listener);if (isDestroyed) {listener.onDestroy();} else if (isStarted) {listener.onStart();} else {listener.onStop();}}void onStart() {isStarted = true;for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {lifecycleListener.onStart();}}void onStop() {isStarted = false;for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {lifecycleListener.onStop();}}void onDestroy() {isDestroyed = true;for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {lifecycleListener.onDestroy();}}
}

好我们来看看Lifecycle 这个接口有啥宝贝：我们要记住这个LifecycleListener 这个接口

*** An interface for listening to Activity/Fragment lifecycle events.*/
public interface Lifecycle {/*** Adds the given listener to the set of listeners managed by this Lifecycle implementation.*/void addListener(LifecycleListener listener);
}

好了，我们还是去看看LifecycleListener 这个接口有啥好东西，好像里面就是一些感觉定义的是生命周期的方法，但是它是如何和ActivityFragmentLifecycle lifecycle 完成这个订阅的观察者模式呢？

/*** An interface for listener to {@link android.app.Fragment} and {@link android.app.Activity} lifecycle events.*/
public interface LifecycleListener {/*** Callback for when {@link android.app.Fragment#onStart()}} or {@link android.app.Activity#onStart()} is called.*/void onStart();/*** Callback for when {@link android.app.Fragment#onStop()}} or {@link android.app.Activity#onStop()}} is called.*/void onStop();/*** Callback for when {@link android.app.Fragment#onDestroy()}} or {@link android.app.Activity#onDestroy()} is* called.*/void onDestroy();
}

好，还记得这个方法么？

 RequestManager supportFragmentGet(Context context, FragmentManager fm) {//对就是这个 SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);RequestManager requestManager = current.getRequestManager();if (requestManager == null) {requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());current.setRequestManager(requestManager);}return requestManager;}//我们把2个方法放在一起看一下  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;}
//它会new SupportRequestManagerFragment(); //最后在SupportRequestManagerFragment内 中实例一个public SupportRequestManagerFragment() {this(new ActivityFragmentLifecycle());}

到了本篇最重要的一个类了RequestManager，我们在上面代码可以看见，将ActivityFragmentLifecycle作为参数，传入到RequestManager 构造方法里了。

  if (requestManager == null) {requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());current.setRequestManager(requestManager);}

那既然这样，我们就去RequestManager里面看看，我们先看看这个类都有啥，代码太多我们只看关键的

//惊喜的发现，RequestManager 居然实现LifecycleListener 接口，如果不记得了请自己在看下源码
public class RequestManager implements LifecycleListener {private final Context context;private final Lifecycle lifecycle; private final RequestManagerTreeNode treeNode;private final RequestTracker requestTracker;private final Glide glide;private final OptionsApplier optionsApplier;private DefaultOptions options;public RequestManager(Context context, Lifecycle lifecycle, RequestManagerTreeNode treeNode) {this(context, lifecycle, treeNode, new RequestTracker(), new ConnectivityMonitorFactory());}RequestManager(Context context, final Lifecycle lifecycle, RequestManagerTreeNode treeNode,RequestTracker requestTracker, ConnectivityMonitorFactory factory) {this.context = context.getApplicationContext();this.lifecycle = lifecycle;this.treeNode = treeNode;this.requestTracker = requestTracker;this.glide = Glide.get(context);this.optionsApplier = new OptionsApplier();ConnectivityMonitor connectivityMonitor = factory.build(context,new RequestManagerConnectivityListener(requestTracker));if (Util.isOnBackgroundThread()) {new Handler(Looper.getMainLooper()).post(new Runnable() {@Overridepublic void run() {lifecycle.addListener(RequestManager.this);}});} else {lifecycle.addListener(this);  //看到这里没有，将RequestManager作为观察者，添加到集合里了}lifecycle.addListener(connectivityMonitor);}
}

   lifecycle.addListener(this);  看到这里没有，将RequestManager作为观察者，添加到集合里了。

我们来看看RequestManager如何处理生命周期的？如何解决glide生命周期和activity、fragment等进行同步的，

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

我们这里在在看看 resumeRequests();方法，其他的实现，请同学自己看下源码，

 public void resumeRequests() {Util.assertMainThread();requestTracker.resumeRequests();}

接着往下看

  /**开始执行请求* Starts any not yet completed or failed requests.*/public void resumeRequests() {isPaused = false;for (Request request : Util.getSnapshot(requests)) {if (!request.isComplete() && !request.isCancelled() && !request.isRunning()) {request.begin();}}pendingRequests.clear();}

好了，到目前为止我们将with的方法说完了，不知道你看懂没有，没有看懂的话，我建议按照这个源码自己多走几遍就好了。

我们来总结下一些关键的类：
RequestManagerRetriever SupportRequestManagerFragment RequestManager

关键的接口： Lifecycle ActivityFragmentLifecycle LifecycleListener

我们在走一遍流程：
Glide.with–> RequestManagerRetriever retriever.get(context)—>retriever.supportFragmentGet(activity, fm)—>retriever.getSupportRequestManagerFragment(FragmentManager fm)

推荐一个比较好的建模工具powerdesigner

附上glide的调用时序图：

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