LifecycleRegistry实例何时开始侦听LifecycleOwner的生命周期更改? [英] When does a LifecycleRegistry instance start listening to LifecycleOwner's lifecycle changes?

问题描述

我已经开始学习架构组件，但是找不到一件事.

I've started learning architecture components, but can't find one thing.

LifecycleFragment 只会创建一个新的 LifecycleRegistry 对象，该对象不会开始观察片段的生命周期.

LifecycleFragment just creates a new LifecycleRegistry object, which does not start observing the fragment's lifecycle.

例如，当我们将其放入

I guess the LifecycleRegistry object starts listening to the fragment's lifecycle when we, for example, put it into LiveData.observe() as first param, but I haven't found any proof of this in source code.

问题: LifecycleRegistry 对象的时间和方式开始观察片段的生命周期并刷新LifecycleRegistry.mState?

Question: When and how does a LifecycleRegistry object start to observe a fragment's lifecycle and refresh LifecycleRegistry.mState?

推荐答案

有一个名为LifecycleRuntimeTrojanProvider的ContentProvider，它已合并到应用程序的AndroidManifest.xml中.在其onCreate方法中，它初始化了一个称为LifecycleDispatcher的单例，该单例负责更新所有LifecycleRegistry实例.

There is a ContentProvider called LifecycleRuntimeTrojanProvider that is merged into the app's AndroidManifest.xml. In its onCreate method it initializes a singleton called LifecycleDispatcher, which is responsible for updating all LifecycleRegistry instances.

LifecycleDispatcher使用自API 14以来就一直存在的Application.registerActivityLifecycleCallbacks 方法在创建新活动时得到通知.此时，它将ReportFragment的实例注入到活动中. ReportFragment如有必要，使用Fragment生命周期回调来更新活动的LifecycleRegistry，如下所示:

LifecycleDispatcher uses the Application.registerActivityLifecycleCallbacks method that has been around since API 14 to get notified when a new activity is created. At this point it injects an instance of ReportFragment into the activity. The ReportFragment uses the Fragment lifecycle callbacks to update the activity's LifecycleRegistry if necessary, like this:

@Override
public void onStop() { // Showing onStop as example
    super.onStop();
    dispatch(Lifecycle.Event.ON_STOP);
}

private void dispatch(Lifecycle.Event event) {
    if (getActivity() instanceof LifecycleRegistryOwner) {
        ((LifecycleRegistryOwner) getActivity()).getLifecycle().handleLifecycleEvent(event);
    }
}

如果新活动是FragmentActivity，则LifecycleDispatcher调用

If the new activity is a FragmentActivity, the LifecycleDispatcher calls FragmentManager.registerFragmentLifecycleCallbacks to get notified of the activity's fragments lifecycle events. It relays the onFragmentCreated, onFragmentStarted and onFragmentResumed callbacks to the LifecycleRegistry in case the fragment is a LifecycleRegistryOwner, in the same way as before.

在片段上调用相应的回调之后，将调用onFragmentPaused，onFragmentStopped和onFragmentDestroyed回调，但是必须在之前调用LifecycleObserver回调.因此，无论何时创建片段，LifecycleDispatcher都会将LifecycleDispatcher.DestructionReportFragment的实例注入其中. DestructionReportFragment的生命周期回调用于为暂停，停止和销毁事件更新注册表.

The onFragmentPaused, onFragmentStopped, and onFragmentDestroyed callbacks are called after the corresponding callbacks are called on the fragment, but the LifecycleObserver callbacks must be called before. So whenever a fragment is created, the LifecycleDispatcher injects an instance of LifecycleDispatcher.DestructionReportFragment into it. The DestructionReportFragment's lifecycle callbacks are used to update the registry for the pause, stop and destroy events.

我无法链接到该代码，因为它尚未发布，但是将库添加到项目后，您可以在Android Studio中浏览它.

I can't link to the code because it hasn't been released yet, but you can browse it in Android Studio after you add the library to your project.

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