PeopleInSpace

Minimal Kotlin Multiplatform project using Jetpack Compose and SwiftUI. Currently running on

• Android
• iOS
• watchOS
• macOS

It makes use of basic API (http://open-notify.org/Open-Notify-API/People-In-Space/) to show list of people currently in space (inspired by https://kousenit.org/2019/12/19/a-few-astronomical-examples-in-kotlin/)! The list is shown on Android using Jetpack Compose and on iOS using SwiftUI

Note: You need to use Android Studio v4.1 (currently on Canary 5). Have tested on XCode v11.3

Update Jan 14th 2020: This now also includes WatchOS version thanks to Neal Sanche

The following is pretty much all the code used (along with gradle files/resources etc). I did say it was minimal!!

Update Jan 25th 2020: Have added SQLDelight support for locally persisting data (across all the platforms). I haven't updated code below yet as I think it still has value in demonstrating what a minimum Kotlin Multiplatform project would be.

Update April 15th 2020: Added macOS support

iOS SwiftUI Code

struct ContentView: View {
    @ObservedObject var peopleInSpaceViewModel = PeopleInSpaceViewModel(repository: PeopleInSpaceRepository())

    var body: some View {
        NavigationView {
            List(peopleInSpaceViewModel.people, id: \.name) { person in
                PersonView(person: person)
            }
            .navigationBarTitle(Text("PeopleInSpace"), displayMode: .large)
            .onAppear(perform: {
                self.peopleInSpaceViewModel.fetch()
            })
        }
    }
}

struct PersonView : View {
    var person: Assignment

    var body: some View {
        HStack {
            VStack(alignment: .leading) {
                Text(person.name).font(.headline)
                Text(person.craft).font(.subheadline)
            }
        }
    }

WatchOS SwiftUI Code

struct ContentView: View {
    @ObservedObject var peopleInSpaceViewModel = PeopleInSpaceViewModel(repository: PeopleInSpaceRepository())
    
    var body: some View {
        VStack {
            List(peopleInSpaceViewModel.people, id: \.name) { person in
                PersonView(person: person)
            }
            .onAppear(perform: {
                self.peopleInSpaceViewModel.fetch()
            })
        }
    }
}

struct PersonView : View {
    var person: Assignment
    
    var body: some View {
        NavigationLink(person.name, destination: Text(person.craft).font(.subheadline))
    }
}

iOS Swift ViewModel

class PeopleInSpaceViewModel: ObservableObject {
    @Published var people = [Assignment]()

    private let repository: PeopleInSpaceRepository
    init(repository: PeopleInSpaceRepository) {
        self.repository = repository
    }
    
    func fetch() {
        repository.fetchPeople(success: { data in
            self.people = data
        })
    }
}

Android Jetpack Compose code

class MainActivity : AppCompatActivity() {
    private val peopleInSpaceViewModel: PeopleInSpaceViewModel by viewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            mainLayout(peopleInSpaceViewModel)
        }
    }
}

@Composable
fun mainLayout(peopleInSpaceViewModel: PeopleInSpaceViewModel) {
    MaterialTheme {
        val people = +observe(peopleInSpaceViewModel.peopleInSpace)
        Column {
            people?.forEach { person ->
                Row(person)
            }
        }
    }
}


@Composable
fun Row(person: Assignment) {
    Padding(16.dp) {
        Text(text = "${person.name} (${person.craft})")
    }
}

Android Kotlin ViewModel

class PeopleInSpaceViewModel(peopleInSpaceRepository: PeopleInSpaceRepository) : ViewModel() {
    val peopleInSpace = MutableLiveData<List<Assignment>>(emptyList())

    init {
        viewModelScope.launch {
            val people = peopleInSpaceRepository.fetchPeople()
            peopleInSpace.value = people
        }
    }
}

Shared Kotlin Repository

class PeopleInSpaceRepository {
    private val peopleInSpaceApi = PeopleInSpaceApi()

    suspend fun fetchPeople() : List<Assignment> {
        val result = peopleInSpaceApi.fetchPeople()
        return result.people
    }


    fun fetchPeople(success: (List<Assignment>) -> Unit) {
        GlobalScope.launch(Dispatchers.Main) {
            success(fetchPeople())
        }
    }
}

Shared Kotlin API Client Code (using Ktor and Kotlinx Serialization library)

@Serializable
data class AstroResult(val message: String, val number: Int, val people: List<Assignment>)

@Serializable
data class Assignment(val craft: String, val name: String)

class PeopleInSpaceApi {
    private val baseUrl = "http://api.open-notify.org"

    private val client by lazy {
        HttpClient() {
            install(JsonFeature) {
                serializer = KotlinxSerializer(Json(JsonConfiguration(strictMode = false)))
            }
        }
    }

    suspend fun fetchPeople() = client.get<AstroResult>("$baseUrl/astros.json")
}

Languages, libraries and tools used

• Kotlin
• Kotlin Corooutines
• Kotlin Serialization
• Ktor client library
• Android Architecture Components
• Koin
• Jetpack Compose
• SwiftUI