ForegroundApp

This is an example app to learn to detect when an App change between Foreground and Background in a Non-single-activity App.

Now is common to found Apps with the Single-activity archiquetures, In this case is easyly detect when the App is in Foreground and Background. We could reach it overriding Activity lifecycle methods like OnStart() or onPause().

In this case we solve the problem in a multi-activity archiquetures app.

In our case, we need to include the androidx.lifecycle library.

We include the dependency in gradle

implementation 'androidx.lifecycle:lifecycle-process:2.4.1'

We need to use a Application class like this:

class ForegroundApp: Application() {

    override fun onCreate() {
        super.onCreate()
    }

}

And also define it in our Manifest.xml

    <application
        android:name=".ForegroundApp"
        ....

At this point we are ready to implement it

At first, ForegroundApp should implementent LifecycleEventObserver

This will be our implementation:

class ForegroundApp: Application(), LifecycleEventObserver 

After that we should override the onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) method.

    override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
        when (event) {
            Lifecycle.Event.ON_START -> {
                Log.d(TAG, "ON START App is in foreground")
                Toast.makeText(this, "App is in foreground", Toast.LENGTH_SHORT).show()
            }
            Lifecycle.Event.ON_PAUSE -> {
                Log.d(TAG, "ON PAUSE")
                Toast.makeText(this, "App is on background", Toast.LENGTH_SHORT).show()
            }
            Lifecycle.Event.ON_STOP -> {
                Log.d(TAG, "ON STOP App is on background")
                Toast.makeText(this, "App is on background", Toast.LENGTH_SHORT).show()
            }
            else -> {}
        }
    }

And the last step is register our lifecycle observer like with this method, that we should include in out Application onCreate() method:

ProcessLifecycleOwner.get().lifecycle.addObserver(this)