生命周期观察器与 Nexus 5 上的生命周期函数不一致

Question

我注意到 Nexus 5 设备在标准 Android 生命周期方法（onCreate、onStart 等）和 LifecycleObserver attached to the AppCompatActivity 生命周期之间存在一些不一致的行为。

打开共享对话框然后再次关闭时出现此问题。

鉴于此 activity:

package gustavkarlsson.se.lifecycleerrordemo

import android.arch.lifecycle.Lifecycle.Event.*
import android.arch.lifecycle.LifecycleObserver
import android.arch.lifecycle.OnLifecycleEvent
import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    init {
        lifecycle.addObserver(object : LifecycleObserver {
            @OnLifecycleEvent(ON_CREATE)
            fun logOnCreate() {
                Log.i(TAG, "Observed: $ON_CREATE")
            }

            @OnLifecycleEvent(ON_START)
            fun logOnStart() {
                Log.i(TAG, "Observed: $ON_START")
            }

            @OnLifecycleEvent(ON_RESUME)
            fun logOnResume() {
                Log.i(TAG, "Observed: $ON_RESUME")
            }

            @OnLifecycleEvent(ON_PAUSE)
            fun logOnPause() {
                Log.i(TAG, "Observed: $ON_PAUSE")
            }

            @OnLifecycleEvent(ON_STOP)
            fun logOnStop() {
                Log.i(TAG, "Observed: $ON_STOP")
            }

            @OnLifecycleEvent(ON_DESTROY)
            fun logOnDestroy() {
                Log.i(TAG, "Observed: $ON_DESTROY")
            }
        })
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.i(TAG, "Ran onCreate")
        email_button.setOnClickListener { openShareDialog() }
    }

    private fun openShareDialog() {
        Intent(Intent.ACTION_SEND).run {
            type = "message/rfc822"
            putExtra(Intent.EXTRA_EMAIL, arrayOf("test@mail.com"))
            putExtra(Intent.EXTRA_SUBJECT, "Subject")
            putExtra(Intent.EXTRA_TEXT, "Text")
            startActivity(Intent.createChooser(this, "Send Email"))
        }
    }

    override fun onStart() {
        super.onStart()
        Log.i(TAG, "Ran onStart")
    }

    override fun onResume() {
        super.onResume()
        Log.i(TAG, "Ran onResume")
    }

    override fun onPause() {
        super.onPause()
        Log.i(TAG, "Ran onPause")
    }

    override fun onStop() {
        super.onStop()
        Log.i(TAG, "Ran onStop")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.i(TAG, "Ran onDestroy")
    }

    companion object {
        private const val TAG = "MainActivity"
    }
}

我希望从观察者和相应的生命周期方法中记录每个生命周期转换。

但是，当我单击按钮打开共享对话框然后再次将其关闭时，不同设备的行为不同。

Samsung Galaxy A3 的表现符合我的预期：

04-03 12:53:55.394 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onCreate
04-03 12:53:55.396 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_CREATE
04-03 12:53:55.398 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onStart
04-03 12:53:55.398 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_START
04-03 12:53:55.404 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onResume
04-03 12:53:55.404 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_RESUME

* Opened share menu *

04-03 12:54:02.431 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_PAUSE
04-03 12:54:02.432 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onPause

* Closed share menu *

04-03 12:54:07.635 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onResume
04-03 12:54:07.636 30109-30109/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_RESUME

Google Nexus 5 观察到 ON_STOP 和 ON_START，即使 onStop 和 onStart 永远不会叫：

04-03 12:51:32.964 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onCreate
04-03 12:51:32.965 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_CREATE
04-03 12:51:32.977 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onStart
04-03 12:51:32.977 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_START
04-03 12:51:32.977 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onResume
04-03 12:51:32.977 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_RESUME

* Opened share menu *

04-03 12:51:42.676 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_PAUSE
04-03 12:51:42.676 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onPause
04-03 12:51:43.395 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_STOP

* Closed share menu *

04-03 12:51:47.791 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Ran onResume
04-03 12:51:47.791 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_START
04-03 12:51:47.791 22062-22062/gustavkarlsson.se.lifecycleerrordemo I/MainActivity: Observed: ON_RESUME

我的问题是：为什么 Nexus 会观察事件，即使相应的生命周期方法从来没有运行？这是错误还是我误解了生命周期？

版本：

com.android.tools.build:gradle:3.1.0
org.jetbrains.kotlin:kotlin-gradle-plugin:1.2.31
com.android.support:support-v4:27.1.0
com.android.support:appcompat-v7:27.1.0
compileSdkVersion 27
targetSdkVersion 27

我已经上传了演示项目 here。

Answer 1

Lifecycle 库将 AppCompatActivity 和 Fragment Lifecycle 对象标记为 CREATED 并在 onSaveInstanceState() 被调用时调度 ON_STOP 而无需等待调用onStop() 方法。这是图书馆的described in the documentation。

文档指出这样做是为了让观察者更容易避免在调用 onSaveInstanceState() 后做会改变 UI 状态的事情，因为如果Activity 或 Fragment 被停止并立即销毁。

您的代码没有任何登录 onSaveInstanceState()，这就是您没有看到此方法调用被记录的原因。

注意。我假设您使用的是 Lifecycle 库的 1.0.0-rc2 或更高版本，该库于 2017 年 10 月 18 日发布（比您提出问题早几个月）。根据 release notes，此行为在该版本中发生了变化。

生命周期观察器与 Nexus 5 上的生命周期函数不一致

Lifecycle observer inconsistent with lifecycle functions on Nexus 5

android

android-lifecycle

android-support-library