Arch Lifecycle¶

Extensions to get ViewModels, use LiveData and observe Lifecycles.

This makes using Android Architecture Components nicer in Kotlin.

Content¶

LifecycleObserver¶

This is a GenericLifecycleObserver sub-interface that has lifecycle state change methods (like onResume(…) or onPause(…)) with default implementations so you override only the ones you need.

ViewModel providers¶

ViewModels are instantiated by host Activity scope.

The activityScope<YourViewModel>() extensions on FragmentActivity and support Fragment return a Lazy<YourViewModel instance that you can use on a delegated property in your Activity or Fragment:

class YourActivity : AppCompatActivity() {
    private val viewModel: YourViewModel by activityScope()
    private val anotherViewModel by activityScope<AnotherViewModel>()
}

class SomeFragment : Fragment() {
    private val viewModel by activityScope<YourViewModel>()
}

LiveData observing and map extension¶

`observe` and `observeNotNull` extension functions on `LifecycleOwner`¶

class YourActivity : AppCompatActivity() {

    private val viewModel by activityScope<YourViewModel>()

    override fun onCreate(savedInstanceState: Bundle?) {
        observe(viewModel.yourLiveData) { data: YourData? ->
            updateUi(data)
        }
        observeNotNull(viewModel.anotherLiveData) {
            doSomething(it.someProperty)
            doSomethingElse(it)
        }
    }
}

`map` extension function on `LiveData`¶

class YourViewModel : ViewModel() {

    val yourLiveData: LiveData<YourData> = createYourLiveData()
    val anotherLiveData = yourLiveData.map { it?.someProperty }
}

Note that the map lambda runs on UI thread, so very light operations like getting a property is right, but long/blocking operations are not (would result in lags or ANRs).

Download¶

implementation "com.louiscad.splitties:splitties-arch-lifecycle:2.1.1"