How to detect when an Android app goes to the background and come back to the foreground... (十年問題)

ProcessLifecycleOwner.md

https://stackoverflow.com/questions/4414171
這問題歷經十年
解決方案也有變化...

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比較優雅的做法是使用:

ProcessLifecycleOwner

https://developer.android.com/reference/android/arch/lifecycle/ProcessLifecycleOwner.html

ProcessLifecycleOwner will dispatch ON_START, ON_RESUME events, as a first activity moves through these events. ON_PAUSE, ON_STOP, events will be dispatched with a delay after a last activity passed through them. This delay is long enough to guarantee that ProcessLifecycleOwner won't send any events if activities are destroyed and recreated due to a configuration change.

It is useful for use cases where you would like to react on your app coming to the foreground or going to the background and you don't need a milliseconds accuracy in receiving lifecycle events.

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https://stackoverflow.com/questions/4414171/#answer-44461605

According to source code, current delay value is 700ms

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中文說明:
ProcessLifecycleOwner 判断 Android 应用程序前后台切换

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WitWicky 歸納出三種解法 [出處]

• Single Activity architecture
• ActivityLifecycleCallback
• LifecycleObserver and ProcessLifecycleOwner

詳細: Foreground or Background ? - Know how to detect your application’s visibility, in Android

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Android ProcessLifecycleOwner by example

參考: gist/AlexZhukovich/Analytics.kt