Jetpack compose - how do I refresh a screen when app returns to foreground

Question

I need to automatically refresh an Android Compose screen when the app returns to the foreground.

I have an that requires permissions and location services.

If the user has switched any of these off a list is drawn of the items that need to be changed. When the user goes to Settings and the app returns to the foreground I would like the list to refresh to reflect the changes.

I am using Compose and Compose navigation. I have looked and I can't figure out the equivalent of onResume lifecycle event that could be used to trigger the refresh.

Any ideas would be gratefully received as I am at a loss.

Answer 1

Using oficial API (requires Lifecycle Runtime Compose 2.7.0):

implementation("androidx.lifecycle:lifecycle-runtime-compose:2.7.0")

The official way to detect Lifecycle.State changes would be using the following code snippet:

val lifecycleOwner = LocalLifecycleOwner.current
val lifecycleState by lifecycleOwner.lifecycle.currentStateFlow.collectAsState()

LaunchedEffect(lifecycleState) {
    // Do something with your state
    // You may want to use DisposableEffect or other alternatives
    // instead of LaunchedEffect
    when (lifecycleState) {
        Lifecycle.State.DESTROYED -> {}
        Lifecycle.State.INITIALIZED -> {}
        Lifecycle.State.CREATED -> {}
        Lifecycle.State.STARTED -> {}
        Lifecycle.State.RESUMED -> {}
    }
}

collectStateAsState is a convenience extension function that collects State changes by using Lifecycle's new property currentStateFlow. So the code above would be the same as doing:

val lifecycleOwner = LocalLifecycleOwner.current
val state by lifecycleOwner.lifecycle.currentStateFlow.collectAsState()

LaunchedEffect(state) {
    // Do something with your state
    // You may want to use DisposableEffect or other alternatives 
    // instead of LaunchedEffect
}

Remember to import androidx.compose.runtime.getValue to access directly the Lifecycle.State.

As mentioned by @HåkonSchia, you can also use variations of DiposableEffect that also take in consideration the Lifecycle:

LifecycleStartEffect(Unit) {
    // Do something on start or launch effect

    onStopOrDispose {
        // Do something on stop or dispose effect
    }
}

LifecycleResumeEffect(Unit) {
    // Do something on resume or launch effect

    onPauseOrDispose {
        // Do something on pause or dispose effect
    }
}

Old answer:

Compose is not aware of state changes like onPause or onResume, you have to handle it using the parent activity's methods.

An example would be a LiveData instance in your activity that updates each time onResume is executed and observe it as a state in your main parent composable.

Let's take a look at the following example:

class MainActivity : AppCompatActivity() {
    // Use whatever type your prefer/require, this is just an example
    private val exampleLiveData = MutableLiveData("")

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            // Your main composable
            MyApplicationTheme {
                // Save the state into a variable otherwise it won't work
                val state = exampleLiveData.observeAsState()
                Log.d("EXAMPLE", "Recomposing screen - ${state.value}")

                Surface(color = MaterialTheme.colors.background) {
                    Greeting("Android")
                }
            }
        }
    }

    override fun onResume() {
        super.onResume()

        // Save whatever you want in your live data, this is just an example
        exampleLiveData.value = DateTimeFormatter.ISO_INSTANT.format(Instant.now())
    }
}

@Composable
fun Greeting(name: String) {
    Text(text = "Hello $name!")
}

@Preview(showBackground = true)
@Composable
fun DefaultPreview() {
    MyApplicationTheme {
        Greeting("Android")
    }
}

As you can see in this example, I have a LiveData property in my activity that containts a String. Whenever onResume is executed the property is updated with the new timestamp and the observing composable is recomposed.