arch-lifecycle

Arch Lifecycle

Extensions to get ViewModels, use LiveData and observe Lifecycles.

Supported platforms: Android.

This makes using Android Architecture Components nicer in Kotlin.

Setup

This dependency is not included in any of the fun-packs, because we don't believe all apps need its content nowadays.

Add it with refreshVersions: Splitties.archLifecycle.

For reference, the maven coordinates of this module are com.louiscad.splitties:splitties-arch-lifecycle.

Content

LifecycleObserver

This is a LifecycleEventObserver 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

AndroidX Activity KTX and Fragment KTX provide convenient delegates to get a ViewModel subclass instance, but they lack a facility when you need to pass arguments to a ViewModel.

Splitties brings a version that takes a lambda, allowing you to run any logic before instantiating the ViewModel, including accessing the created Activity or Fragment.

class YourActivity : AppCompatActivity() {

    private val viewModel: SomeViewModel by viewModels() // From androidx.activity KTX
    private val anotherViewModel by viewModels<AnotherViewModel>() // From androidx.activity KTX

    private val yourViewModel by viewModels { // From Splitties
        YourViewModel(someParams)
    }
}

class SomeFragment : Fragment() {

    private val viewModel: SomeViewModel by viewModels() // From androidx.activity KTX
    private val anotherViewModel: AnotherViewModel by activityViewModels() // From androidx.activity KTX

    private val yourViewModel by viewModels { // From Splitties
        YourViewModel(someParams)
    }
}

LiveData observing and map extension

observe and observeNotNull extension functions on LifecycleOwner

These extensions make observing a LiveData null-safe (despite LiveData not being null-safe itself), giving you the choice of whether you want to deal with nulls or ignore them.

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).