不建议使用onActivityCreated，如何正确使用LifecycleObserver? [英] onActivityCreated is deprecated, how to properly use LifecycleObserver?

问题描述

Google在Android上弃用片段的onActivityCreated()，建议使用LifeCycleObserver:

Google deprecate fragment’s onActivityCreated() on Android and recommend to use LifeCycleObserver:

 To get a callback specifically when a Fragment activity's
     * {@link Activity#onCreate(Bundle)} is called, register a
     * {@link androidx.lifecycle.LifecycleObserver} on the Activity's
     * {@link Lifecycle} in {@link #onAttach(Context)}, removing it when it receives the
     * {@link Lifecycle.State#CREATED} callback.

因此，我尝试以推荐的方式进行操作，但是只能在Logcat中观察到的状态只是状态:INITIALIZED .

So I try to make it in recommended way, but only state I can observe in Logcat is just State: INITIALIZED.

 private lateinit var lifecycleObserver: LifecycleObserver

 override fun onAttach(context: Context) {
    super.onAttach(context)

    hostActivity = context as HostActivity

    lifecycleObserver = object : LifecycleObserver {

        @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
        fun onCreate() {
            Logger.tag("SOME-TAG")d("State: ${lifecycle.currentState}")

            if(lifecycle.currentState.isAtLeast(Lifecycle.State.CREATED)) {
                Logger.tag("SOME-TAG").d("CREATED")
                hostActivity.lifecycle.removeObserver(lifecycleObserver)
            }
        }
    }

    hostActivity.lifecycle.addObserver(lifecycleObserver)
}

上面的代码有什么问题?

What is wrong in code above?

更新1 :好像我忘了使用hostActivity.lifecycle.currentState并检查了片段的生命周期，而不是Activity生命周期.

UPDATE 1: Looks like I forgot to use hostActivity.lifecycle.currentState and checked fragment's lifecycle instead of Activities lifecycle.

更新2 :由Google建议的方法不适用于 1个主机活动和2个片段，当您从一个按钮单击到另一个按钮时，导致onAttach从未调用，而是onActivityCreated调用了.

UPDATE 2: Suggested by Google approach not worked for 1 Host activity and 2 fragments when you click back button from one to another, cause onAttach never called, but onActivityCreated called.

推荐答案

我是通过以下方式实现的:

I did it in next way:

class MyActivityObserver(
    private val update: () -> Unit
) : DefaultLifecycleObserver {

    override fun onCreate(owner: LifecycleOwner) {
        super.onCreate(owner)
        owner.lifecycle.removeObserver(this)
        update()
    }
}

并在onAttach(或其他生命周期方法)片段中使用它，例如:

and use it in fragments onAttach (or another lifecycle method) like:

myActivity.lifecycle.addObserver(MyActivityObserver {
    myOnActivityCreated()
})

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