Glide(一)生命周期绑定

• Glide 的解耦方式很独特。
• 相关文章：Fragment 如何跟Activity的生命周期进行绑定
• 1.1 Glide.with()

Glide.with(FragmentActivity activity)// RequestManager with(FragmentActivity activity)

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

public RequestManager get(Activity activity) {    if (Util.isOnBackgroundThread()) {      return get(activity.getApplicationContext());    } else {      assertNotDestroyed(activity);      // 获取当前Activity的FragmentManager，      // 后续用于新见Fragment并绑定到当前FragmentManager，从而获取Fragment的生命周期（同步Activity的生命周期）      android.app.FragmentManager fm = activity.getFragmentManager();      return fragmentGet(activity, fm, null /*parentHint*/);    }  }

• 1.2 这里主要看 RequestManagerFragment

private RequestManager fragmentGet(Context context, android.app.FragmentManager fm,      android.app.Fragment parentHint) {    // a.绑定 RequestManagerFragment 至 FragmentManager ，使RequestManagerFragment 生命周期同步 Activity    RequestManagerFragment current = getRequestManagerFragment(fm, parentHint);    RequestManager requestManager = current.getRequestManager();    if (requestManager == null) {      // TODO(b/27524013): Factor out this Glide.get() call.      Glide glide = Glide.get(context);      requestManager =          // b. 获取一个RequestManager 实例并给当前RequestManagerFragment          factory.build(glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode());      current.setRequestManager(requestManager);    }    return requestManager;  }

• 1.3 绑定 RequestManagerFragment 至 FragmentManager，当前RequestManagerFragment已经有了其生命周期，看下如何实现

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)  RequestManagerFragment getRequestManagerFragment(      final android.app.FragmentManager fm, android.app.Fragment parentHint) {     //a.根据TAG id获取RequestManagerFragment实例    RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);    if (current == null) {      // b. 如果a没获取实例，从内存的map内获取      current = pendingRequestManagerFragments.get(fm);      if (current == null) {        // c. 以上a,b 都没有获取实例，则最后new一个，并put 到内存 map内        current = new RequestManagerFragment();        current.setParentFragmentHint(parentHint);        pendingRequestManagerFragments.put(fm, current);        // fragment 与 FragmentManager 绑定，那么 RequestManagerFragment 有了生命周期        fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();        handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();      }    }    return current;  }

• 1.4 以上步骤中参考 1.2中b操作使得RequestManagerFragment中有RequestManager，RequestManager在构造中将自身添加到Lifecycle中

RequestManager(      Glide glide,      Lifecycle lifecycle,      RequestManagerTreeNode treeNode,      RequestTracker requestTracker,      ConnectivityMonitorFactory factory) {    this.glide = glide;    this.lifecycle = lifecycle;    this.treeNode = treeNode;    this.requestTracker = requestTracker;    ...    if (Util.isOnBackgroundThread()) { // 非主线程      mainHandler.post(addSelfToLifecycle);    } else { // 主线程      lifecycle.addListener(this);    }    lifecycle.addListener(connectivityMonitor);    setRequestOptions(glide.getGlideContext().getDefaultRequestOptions());    glide.registerRequestManager(this);  }  private final Runnable addSelfToLifecycle = new Runnable() {    @Override    public void run() {      lifecycle.addListener(RequestManager.this);    }  };

• 2.1 Fragment 生命周期的传递

public RequestManagerFragment() {    // 构造时初始化ActivityFragmentLifecycle    this(new ActivityFragmentLifecycle());}@SuppressLint("ValidFragment")RequestManagerFragment(ActivityFragmentLifecycle lifecycle) {    this.lifecycle = lifecycle;}// 以下为生命周期的透传 @Override  public void onStart() {    super.onStart();    lifecycle.onStart();  }  @Override  public void onStop() {    super.onStop();    lifecycle.onStop();  }  @Override  public void onDestroy() {    super.onDestroy();    lifecycle.onDestroy();    unregisterFragmentWithRoot();  }

• 2.2 回调所有生命周期的接口
  
  • RequestManagerFragment 下回调所有注册的 RequestManager

@Override  public void removeListener(LifecycleListener listener) {    lifecycleListeners.remove(listener);  }  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();    }  }}

总结

• 1.通过获取 Activity 的FragmentManager，绑定一个空RequestManagerFragment，以同步Activity生命周期
• 2.RequestManagerFragment 中初始化LifecycleListener
• 3.初始化RequestManagerFragment，同事初始化RequestManager，并注册至LifecycleListener
• 4.Activity 触发生命周期时，回调 Fragment，并透传至LifecycleListener,LifecycleListener会回调所有向其注册过的RequestManager
• 综上所得解耦新技能。奉上时序图