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

Compatibility

The latest version of the library uses Kotlin version 1.9.23.
Compatibility versions for older and/or preview Kotlin versions are also available:

Version	Version suffix	Kotlin	Coroutines	AndroidX Lifecycle
latest	-kotlin-2.0.0-RC1	2.0.0-RC1	1.8.0	2.7.0
latest	no suffix	1.9.23	1.8.0	2.7.0
1.0.0-ALPHA-19	no suffix	1.9.22	1.8.0	2.7.0
1.0.0-ALPHA-18	no suffix	1.9.22	1.7.3	2.6.2
1.0.0-ALPHA-16	no suffix	1.9.21	1.7.3	2.6.2
1.0.0-ALPHA-15	no suffix	1.9.20	1.7.3	2.6.2
1.0.0-ALPHA-14	no suffix	1.9.10	1.7.3	2.6.1
1.0.0-ALPHA-13	no suffix	1.9.0	1.7.3	2.6.1
1.0.0-ALPHA-10	no suffix	1.8.22	1.7.2	2.6.1
1.0.0-ALPHA-9	no suffix	1.8.21	1.7.1	2.5.1
1.0.0-ALPHA-8	no suffix	1.8.21	1.7.0	2.5.1
1.0.0-ALPHA-7	no suffix	1.8.21	1.6.4	2.5.1
1.0.0-ALPHA-6	no suffix	1.8.20	1.6.4	2.5.1
1.0.0-ALPHA-4	no suffix	1.8.10	1.6.4	2.5.1
1.0.0-ALPHA-3	no suffix	1.8.0	1.6.4	2.5.1

Kotlin

Add the library to your shared Kotlin module and opt-in to the ExperimentalForeignApi:

kotlin {
    sourceSets {
        all {
            languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
        }
        commonMain {
            dependencies {
                api("com.rickclephas.kmm:kmm-viewmodel-core:1.0.0-ALPHA-20")
            }
        }
    }
}

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.

Alternative

Alternatively you can create extension properties in your iOS source-set yourself: kotlin 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-20")
]

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

CocoaPods

If you like you can also use CocoaPods instead of SPM: ruby pod 'KMMViewModelSwiftUI', '1.0.0-ALPHA-20'

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:

ObservableObject	KMMViewModel
@StateObject	@StateViewModel
@ObservedObject	@ObservedViewModel
@EnvironmentObject	@EnvironmentViewModel
environmentObject(_:)	environmentViewModel(_:)

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(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:).

Cancellable ViewModel

When subclassing your Kotlin ViewModel in Swift you might experience some issues in the way those ViewModels are cleared.

An example of such an issue is when you are using a Combine publisher to observe a Flow through KMP-NativeCoroutines:

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

class TimeTravelViewModel: shared.TimeTravelViewModel {

    private var cancellables = Set<AnyCancellable>()

    override init() {
        super.init()
        createPublisher(for: currentTimeFlow)
            .assertNoFailure()
            .sink { time in print("It's \(time)") }
            .store(in: &cancellables)
    }
}

Since currentTimeFlow is a StateFlow we don't ever expect it to fail, which is why we are using the assertNoFailure. However, in this case you'll notice that the publisher will fail with a JobCancellationException.

The problem here is that before the TimeTravelViewModel is deinited it will already be cleared. Meaning the viewModelScope is cancelled and onCleared is called. This results in the Combine publisher outliving the underlying StateFlow collection.

To solve such issues you should have your Swift ViewModel conform to Cancellable and perform the required cleanup in the cancel function:

class TimeTravelViewModel: shared.TimeTravelViewModel, Cancellable {
    func cancel() {
        cancellables = []
    }
}

KMM-ViewModel will make sure to call the cancel function before the ViewModel is being cleared.