Below solution works from API level 14+
Backgrounding
ComponentCallbacks2 — Looking at the documentation is not 100% clear on how you would use this. However, take a closer look and you will noticed the onTrimMemory method passes in a flag. These flags are typically to do with the memory availability but the one we care about is TRIM_MEMORY_UI_HIDDEN. By checking if the UI is hidden we can potentially make an assumption that the app is now in the background. Not exactly obvious but it should work.
Foregrounding
ActivityLifecycleCallbacks — We can use this to detect foreground by overriding onActivityResumed and keeping track of the current application state (Foreground/Background).
Create our interface that will be implemented by a custom Application class
interface LifecycleDelegate {
fun onAppBackgrounded()
fun onAppForegrounded()
}
Create a class that is going to implement the ActivityLifecycleCallbacks and ComponentCallbacks2 and override onActivityResumed and onTrimMemory methods
// Take an instance of our lifecycleHandler as a constructor parameter
class AppLifecycleHandler(private val lifecycleDelegate: LifecycleDelegate)
: Application.ActivityLifecycleCallbacks, ComponentCallbacks2 // <-- Implement these
{
private var appInForeground = false
// Override from Application.ActivityLifecycleCallbacks
override fun onActivityResumed(p0: Activity?) {
if (!appInForeground) {
appInForeground = true
lifecycleDelegate.onAppForegrounded()
}
}
// Override from ComponentCallbacks2
override fun onTrimMemory(level: Int) {
if (level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
// lifecycleDelegate instance was passed in on the constructor
lifecycleDelegate.onAppBackgrounded()
}
}
}
Now all we need to do is have our custom Application class implement our LifecycleDelegate interface and register.
class App : Application(), LifeCycleDelegate {
override fun onCreate() {
super.onCreate()
val lifeCycleHandler = AppLifecycleHandler(this)
registerLifecycleHandler(lifeCycleHandler)
}
override fun onAppBackgrounded() {
Log.d("Awww", "App in background")
}
override fun onAppForegrounded() {
Log.d("Yeeey", "App in foreground")
}
private fun registerLifecycleHandler(lifeCycleHandler: AppLifecycleHandler) {
registerActivityLifecycleCallbacks(lifeCycleHandler)
registerComponentCallbacks(lifeCycleHandler)
}
}
In Manifest set the CustomApplicationClass
<application
android:name=".App"
