A SwiftUI macro to use inside a Apple Kotlin multiplatform project for wrapping a Kotlin ViewModel into a SwiftUI ObservableObject, based on the SKIE library.
The goal of this macro is to increase the iOS development experience by removing the complexity of using a Kotlin ViewModel inside an iOS application written in Swift and also respecting the Lifecycle.
For example, instead of using KotlinInt/KotlinInt?, we're using Int/Int?, it can work with Float/Double/...
Currently supported Kotlin types : dataclass/class, int, double, float, bool, uint, Long (swift int64), please make an issue for more.
You can also bind List but only with type Class and String.
Note
The macro can create uniderectional and bidirectionel binding
See the sample for a full and detailed example.
KMP ViewModel
iOS SwiftUI macro
KTViewModelBuilder/Sample/iosApp/iosApp/ExampleScreen.swift
Lines 13 to 29 in 983bedf
public class ExampleViewModel : ViewModel() {
public var bidirectionalString: MutableStateFlow<String> = MutableStateFlow<String>("SOME INPUT")
public var bidirectionalBoolean: MutableStateFlow<Boolean> = MutableStateFlow<Boolean>(false)
public var bidirectionalInt: MutableStateFlow<Int?> = MutableStateFlow<Int?>(42)
public var bidirectionalLong: MutableStateFlow<Long> = MutableStateFlow<Long>(424242L)
private val _stringData = MutableStateFlow("Some Data")
public val stringData: StateFlow<String> = _stringData
private val _intNullableData = MutableStateFlow<Int?>(null)
public val intNullableData: StateFlow<Int?> = _intNullableData
private val _randomValue = MutableStateFlow(0)
public val randomValue: StateFlow<Int> = _randomValue
private val _entityData = MutableStateFlow<MyData?>(MyData())
public val entityData: StateFlow<MyData?> = _entityData
public fun randomizeValue() {
_randomValue.value = (0..100).random()
}
}The macro generate a SwiftUI ViewModel from the content of the Kotlin ExampleViewModel class.
@ktViewModelBinding(ofType: ExampleViewModel.self,
publishing:
.init(\.stringData, String.self),
.init(\.intNullableData, Int?.self),
.init(\.randomValue, Double.self),
.init(\.entityData, MyData?.self),
.init(\.bidirectionalString, String.self, true),
.init(\.bidirectionalInt, Int?.self, true),
.init(\.bidirectionalBoolean, Bool.self, true),
.init(\.bidirectionalLong, Int64.self, true)
)
class MyMainScreenViewModel: ObservableObject {}Generated content
class MyMainScreenViewModel : ObservableObject {
private let viewModelStore = ViewModelStore()
@Published private(set) var stringData: String
@Published private(set) var intNullableData: Int?
@Published private(set) var randomValue: Double
@Published private(set) var entityData: MyData?
@Published var bidirectionalString: String {
didSet {
instance.bidirectionalString.value = bidirectionalString
}
}
@Published var bidirectionalInt: Int? {
didSet {
instance.bidirectionalInt.value = bidirectionalInt != nil ? KotlinInt(integerLiteral: bidirectionalInt!) : nil
}
}
@Published var bidirectionalBoolean: Bool {
didSet {
instance.bidirectionalBoolean.value = KotlinBoolean(bool: bidirectionalBoolean)
}
}
@Published var bidirectionalLong: Int64 {
didSet {
instance.bidirectionalLong.value = KotlinLong(value: bidirectionalLong)
}
}
init(_ viewModel: ExampleViewModel) {
self.viewModelStore.put(key: "ExampleViewModelKey", viewModel: viewModel)
self.stringData = viewModel.stringData.value
print("INIT stringData : " + String(describing: viewModel.stringData.value))
self.intNullableData = viewModel.intNullableData.value?.intValue
print("INIT intNullableData : " + String(describing: viewModel.intNullableData.value))
self.randomValue = viewModel.randomValue.value.doubleValue
print("INIT randomValue : " + String(describing: viewModel.randomValue.value))
self.entityData = viewModel.entityData.value
print("INIT entityData : " + String(describing: viewModel.entityData.value))
self.bidirectionalString = viewModel.bidirectionalString.value
print("INIT bidirectionalString : " + String(describing: viewModel.bidirectionalString.value))
self.bidirectionalInt = viewModel.bidirectionalInt.value?.intValue
print("INIT bidirectionalInt : " + String(describing: viewModel.bidirectionalInt.value))
self.bidirectionalBoolean = viewModel.bidirectionalBoolean.value.boolValue
print("INIT bidirectionalBoolean : " + String(describing: viewModel.bidirectionalBoolean.value))
self.bidirectionalLong = viewModel.bidirectionalLong.value.int64Value
print("INIT bidirectionalLong : " + String(describing: viewModel.bidirectionalLong.value))
}
var instance: ExampleViewModel {
self.viewModelStore.get(key: "ExampleViewModelKey") as! ExampleViewModel
}
func start() async {
await withTaskGroup(of: (Void).self) {
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.stringData where self != nil {
if value != self?.stringData {
#if DEBUG
print("UPDATING TO VIEW stringData : " + String(describing: value))
#endif
self?.stringData = value
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.intNullableData where self != nil {
if value?.intValue != self?.intNullableData {
#if DEBUG
print("UPDATING TO VIEW intNullableData : " + String(describing: value))
#endif
self?.intNullableData = value?.intValue
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.randomValue where self != nil {
if value.doubleValue != self?.randomValue {
#if DEBUG
print("UPDATING TO VIEW randomValue : " + String(describing: value))
#endif
self?.randomValue = value.doubleValue
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.entityData where self != nil {
if value != self?.entityData {
#if DEBUG
print("UPDATING TO VIEW entityData : " + String(describing: value))
#endif
self?.entityData = value
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.bidirectionalString where self != nil {
if value != self?.bidirectionalString {
#if DEBUG
print("UPDATING TO VIEW bidirectionalString : " + String(describing: value))
#endif
self?.bidirectionalString = value
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.bidirectionalInt where self != nil {
if value?.intValue != self?.bidirectionalInt {
#if DEBUG
print("UPDATING TO VIEW bidirectionalInt : " + String(describing: value))
#endif
self?.bidirectionalInt = value?.intValue
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.bidirectionalBoolean where self != nil {
if value.boolValue != self?.bidirectionalBoolean {
#if DEBUG
print("UPDATING TO VIEW bidirectionalBoolean : " + String(describing: value))
#endif
self?.bidirectionalBoolean = value.boolValue
}
}
}
$0.addTask { @MainActor [weak self] in
for await value in self!.instance.bidirectionalLong where self != nil {
if value.int64Value != self?.bidirectionalLong {
#if DEBUG
print("UPDATING TO VIEW bidirectionalLong : " + String(describing: value))
#endif
self?.bidirectionalLong = value.int64Value
}
}
}
}
}
deinit {
self.viewModelStore.clear()
}
}The properties of the ViewModel can be directly used from the viewModel property and the method from viewModel.instance.
The binding must be triggered from a SwiftUI task modifier; it will start the Observability of the declared properties.
struct ExampleScreen: View {
// Initialize the ViewModel, binding and lifecycle
@StateObject var viewModel = MyMainScreenViewModel(ExampleViewModel())
var body: some View {
VStack {
Text("STRING VALUE \(viewModel.stringData)")
Text("NULL VALUE \(String(describing: viewModel.intNullableData))")
Text("RANDOM VALUE \(viewModel.randomValue)")
Text("BIDI STRING VALUE \(viewModel.bidirectionalString)")
Text("BIDI BOOLEAN SHEET VALUE \(viewModel.bidirectionalBoolean)") // see app logs for update
TextField("MY bidirectional String", text: $viewModel.bidirectionalString) // see app logs for update
Button {
viewModel.instance.randomizeValue()
} label: {
Text("randomizeValue")
}
Button("Show Sheet") {
viewModel.bidirectionalBoolean.toggle()
}
.sheet(isPresented: $viewModel.bidirectionalBoolean) {
SheetView()
}
}.task {
// start the ViewModel lifecycle and keep it alive until the view disappear
await viewModel.start()
}
}
}As this solution is based on Kotlin multiplatform and SKIE, some requirements need to be met.
Please follow the installation step of the library.
- Add in your .toml or .gradle the following dependency
androidx-lifecycle-viewmodel = { module = "androidx.lifecycle:lifecycle-viewmodel", version.ref = "androidx_lifecycle_version" }- Then follow this configuration or equivalent
listOf(
iosX64(),
iosArm64(),
iosSimulatorArm64()
).forEach {
it.binaries.framework {
baseName = "shared"
isStatic = true
export(libs.androidx.lifecycle.viewmodel) // !! export the library for the iOS target, so it can be accessible from swift code !!
}
}
sourceSets {
commonMain.dependencies {
api(libs.androidx.lifecycle.viewmodel) // the library itself
}
}Finally, add this package to your application swift package dependencies.
https://github.com/frankois944/KTViewModelBuilder
That's all you need.
A Sample is available in this repository, which has a shared library and an iOS/Android app.