goooler / kmm-viewmodel

Library to share Kotlin ViewModels with SwiftUI

KMM-ViewModel

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

Compatibility

The latest version of the library uses Kotlin version 1.8.20.
Compatibility versions for newer Kotlin versions are also available:

Version	Version suffix	Kotlin	Coroutines
latest	no suffix	1.8.20	1.6.4
1.0.0-ALPHA-4	no suffix	1.8.10	1.6.4
1.0.0-ALPHA-3	no suffix	1.8.0	1.6.4

Kotlin

Add the library to your shared Kotlin module:

dependencies {
    implementation("com.rickclephas.kmm:kmm-viewmodel-core:<version>")
}

Create your ViewModels almost as you would in Android:

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

// 1: use KMMViewModel instead of ViewModel
open class TimeTravelViewModel: KMMViewModel() {

    private val clockTime = Clock.time

    /**
     * A [StateFlow] that emits the actual time.
     */
    val actualTime = clockTime.map { formatTime(it) }
        // 2: supply viewModelScope to your stateIn calls
        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(), "N/A")

    // 3: supply viewModelScope to your MutableStateFlows
    private val _travelEffect = MutableStateFlow<TravelEffect?>(viewModelScope, null)
    /**
     * A [StateFlow] that emits the applied [TravelEffect].
     */
    val travelEffect = _travelEffect.asStateFlow()
}

You need to use viewModelScope wherever possible to propagate state changes to iOS.
In other cases you can access the ViewModelScope.coroutineScope property directly.

KMP-NativeCoroutines

Use the @NativeCoroutinesState annotation from KMP-NativeCoroutines to turn your StateFlows into properties in Swift:

@NativeCoroutinesState
val travelEffect = _travelEffect.asStateFlow()

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

Alternative

Alternatively you can create extension properties in your iOS source-set yourself:

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

Android

Add the library to your Android module:

dependencies {
    implementation("com.rickclephas.kmm:kmm-viewmodel-core:<version>")
}

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: 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: "<version>")
]

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

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
}