KMM-ViewModel

A library that allows you to share ViewModels between Android and iOS.

Compatibility

The latest version of the library uses Kotlin version 1.9.10.
Compatibility versions for older and/or preview Kotlin versions are also available:

Kotlin

Add the library to your shared Kotlin module:

dependencies {
    api("com.rickclephas.kmm:kmm-viewmodel-core:1.0.0-ALPHA-14")
}

And create your ViewModels:

import com.rickclephas.kmm.viewmodel.KMMViewModel
import com.rickclephas.kmm.viewmodel.MutableStateFlow
import com.rickclephas.kmm.viewmodel.stateIn

open class TimeTravelViewModel: KMMViewModel() {

    private val clockTime = Clock.time

    /**
     * A [StateFlow] that emits the actual time.
     */
    val actualTime = clockTime.map { formatTime(it) }
        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(), "N/A")

    private val _travelEffect = MutableStateFlow<TravelEffect?>(viewModelScope, null)
    /**
     * A [StateFlow] that emits the applied [TravelEffect].
     */
    val travelEffect = _travelEffect.asStateFlow()
}

As you might notice it isn't much different from an Android ViewModel.
The most obvious difference is the KMMViewModel superclass:

- import androidx.lifecycle.ViewModel
+ import com.rickclephas.kmm.viewmodel.KMMViewModel

- open class TimeTravelViewModel: ViewModel() {
+ open class TimeTravelViewModel: KMMViewModel() {

Besides that there are only 2 minor differences.
The first being a different import for stateIn:

- import kotlinx.coroutines.flow.stateIn
+ import com.rickclephas.kmm.viewmodel.stateIn

        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(), "N/A")

And the second being a different MutableStateFlow constructor:

- import kotlinx.coroutines.flow.MutableStateFlow
+ import com.rickclephas.kmm.viewmodel.MutableStateFlow

-    private val _travelEffect = MutableStateFlow<TravelEffect?>(null)
+    private val _travelEffect = MutableStateFlow<TravelEffect?>(viewModelScope, null)

These minor differences will make sure that any state changes are propagated to iOS.

Note: viewModelScope is a wrapper around the actual CoroutineScope which can be accessed via the ViewModelScope.coroutineScope property.

KMP-NativeCoroutines

I highly recommend you to use the @NativeCoroutinesState annotation from KMP-NativeCoroutines to turn your StateFlows into properties in Swift:

@NativeCoroutinesState
val travelEffect = _travelEffect.asStateFlow()

Checkout the KMP-NativeCoroutines README for more information and installation instructions.

val TimeTravelViewModel.travelEffectValue: TravelEffect?
    get() = travelEffect.value

Android

Use the view model like you would any other Android view model:

class TimeTravelFragment: Fragment(R.layout.fragment_time_travel) {
    private val viewModel: TimeTravelViewModel by viewModels()
}

Note: improved support for Jetpack Compose is coming soon.

Swift

Add the Swift package to your Package.swift file:

dependencies: [
    .package(url: "https://github.com/rickclephas/KMM-ViewModel.git", from: "1.0.0-ALPHA-14")
]

Or add it in Xcode by going to File > Add Packages... and providing the URL: https://github.com/rickclephas/KMM-ViewModel.git.

pod 'KMMViewModelSwiftUI', '1.0.0-ALPHA-14'

Create a KMMViewModel.swift file with the following contents:

import KMMViewModelCore
import shared // This should be your shared KMM module

extension Kmm_viewmodel_coreKMMViewModel: KMMViewModel { }

After that you can use your view model almost as if it were an ObservableObject.
Just use the view model specific property wrappers and functions:

E.g. to use the TimeTravelViewModel as a StateObject:

import SwiftUI
import KMMViewModelSwiftUI
import shared // This should be your shared KMM module

struct ContentView: View {
    @StateViewModel var viewModel = TimeTravelViewModel()
}

It's also possible to subclass your view model in Swift:

import Combine
import shared // This should be your shared KMM module

class TimeTravelViewModel: shared.TimeTravelViewModel {
    @Published var isResetDisabled: Bool = false
}

Child view models

You'll need some additional logic if your KMMViewModels expose child view models.

First make sure to use the NativeCoroutinesRefinedState annotation instead of the NativeCoroutinesState annotation:

class MyParentViewModel: KMMViewModel() {
    @NativeCoroutinesRefinedState
    val myChildViewModel: StateFlow<MyChildViewModel?> = MutableStateFlow(null)
}

After that you should create a Swift extension property using the childViewModel(_, at:) function:

extension MyParentViewModel {
    var myChildViewModel: MyChildViewModel? {
        childViewModel(__myChildViewModel, at: \.__myChildViewModel)
    }
}

This will prevent your Swift view models from being deallocated too soon.

Note: for lists, sets and dictionaries containing view models there is childViewModels(_, at:).