kotlin-multiplatform

// commonMain - expect declaration
expect class PlatformContext
 
expect fun getPlatformName(): String
 
expect fun createHttpClient(): HttpClient
 
// androidMain - actual implementation
actual class PlatformContext(val context: android.content.Context)
 
actual fun getPlatformName(): String = "Android ${Build.VERSION.SDK_INT}"
 
actual fun createHttpClient(): HttpClient = HttpClient(OkHttp) {
    install(ContentNegotiation) { json() }
}
 
// iosMain - actual implementation
actual class PlatformContext
 
actual fun getPlatformName(): String = UIDevice.currentDevice.systemName()
 
actual fun createHttpClient(): HttpClient = HttpClient(Darwin) {
    install(ContentNegotiation) { json() }
}

// commonMain
class ApiClient(private val httpClient: HttpClient) {
    suspend fun getUsers(): List<User> {
        return httpClient.get("https://api.example.com/users").body()
    }
 
    suspend fun createUser(input: CreateUserInput): User {
        return httpClient.post("https://api.example.com/users") {
            contentType(ContentType.Application.Json)
            setBody(input)
        }.body()
    }
}
 
@Serializable
data class User(
    val id: String,
    val name: String,
    val email: String,
)

-- src/commonMain/sqldelight/com/example/UserQueries.sq
CREATE TABLE user (
    id TEXT NOT NULL PRIMARY KEY,
    name TEXT NOT NULL,
    email TEXT NOT NULL,
    cached_at INTEGER NOT NULL
);
 
selectAll:
SELECT * FROM user ORDER BY name;
 
insertOrReplace:
INSERT OR REPLACE INTO user (id, name, email, cached_at)
VALUES (?, ?, ?, ?);
 
deleteById:
DELETE FROM user WHERE id = ?;

// commonMain - Shared composable
@Composable
fun UserListScreen(viewModel: UserListViewModel) {
    val users by viewModel.users.collectAsState()
    val isLoading by viewModel.isLoading.collectAsState()
 
    Scaffold(
        topBar = { TopAppBar(title = { Text("Users") }) }
    ) { padding ->
        if (isLoading) {
            CircularProgressIndicator(modifier = Modifier.padding(padding))
        } else {
            LazyColumn(modifier = Modifier.padding(padding)) {
                items(users) { user ->
                    UserRow(user = user, onClick = { viewModel.onUserClick(user.id) })
                }
            }
        }
    }
}

// iosApp - Using shared Kotlin code from Swift
import shared
 
class UserViewController: UIViewController {
    private let viewModel = UserListViewModel()
 
    override func viewDidLoad() {
        super.viewDidLoad()
        viewModel.users.collect(collector: FlowCollector { users in
            // Update UI with users
        })
    }
}

// build.gradle.kts
kotlin {
    iosX64()
    iosArm64()
    iosSimulatorArm64()
 
    cocoapods {
        summary = "Shared module"
        homepage = "https://example.com"
        ios.deploymentTarget = "16.0"
        framework { baseName = "shared" }
    }
}

// commonTest
class UserRepositoryTest {
    private val fakeApi = FakeApiClient()
    private val repository = UserRepository(fakeApi)
 
    @Test
    fun fetchUsersReturnsListFromApi() = runTest {
        fakeApi.setUsers(listOf(User("1", "Alice", "alice@test.com")))
 
        val users = repository.getUsers()
 
        assertEquals(1, users.size)
        assertEquals("Alice", users.first().name)
    }
}