Pacemaker (iOS & Android) [KMP]

Run together! A running companion monitoring the heart rate of a group of people doing sports together.

Supports

  • External Bluetooth (LE) heart rate monitors (tested with Polar H10)
  • iPhone <-> iPhone connections (No internet necessary, BLE)
  • Android <-> Android connections (No internet necessary, BLE)
  • iPhone <-> Android connections (No internet necessary, BLE)

Planned

WatchOS support (via UWB chip and Internet)

Screenshots

Screenshot iOS Screenshot iOS Screenshot iOS

Install

Technical Details

Kotlin Multiplatform

This application is built as a Test/Dogfooding project for Kotlin/Multiplatform, Compose and JetBrains Fleet.

Architecture

No! ViewModels!: This project uses ‘State Actors’ instead.

The State Actor pattern used in ‘Pacemaker’ can be defined by two high level concepts:

Events

Every component in the application can emit any kind of event, including intents. Example: Some UI button that emits an event to the application

@Composable
fun MyButton() {
    Button(
        onClick = Launching { LoginIntent.emit() }
    ) {
        // ...
    }
}

State Producers

States can be produced and observed. Lets look at the producing site first: Lets take the classic login example:

data class LoginState(val email: String, val password: String, val isLoggedIn: Boolean) : State {
    companion object Key : State.Key<LoginState> {
        val default get() = LoginState(email = "", password = "", isLoggedIn = false)
    }
}

fun CoroutineScope.launchLoginStateActor() = launchStateProducer(LoginState) {
    var state = LoginState.default

    collectEventsAsync<EmailChangedEvent> {
        state = state.copy(email = it.email)
        state.emit()
    }

    collectEventsAsync<PasswordChangedEvent> {
        state = state.copy(password = it.password)
        state.emit()
    }

    collectEventsAsync<LoginIntent> {
        val isLoggedIn = attemptLogin(state.email, state.password)
        state = state.copy(isLoggedIn = isLoggedIn)
        state.emit()
    }
}

Such states can then be used in the Application UI/Frontend easily

@Composable
fun MyLoginScreen() {
    val loginState by LoginState.collectAsState()
    MyLoginScreen(
        email = loginState.email,
        password = loginState.password
    )
}

@Composable
fun MyLoginScreen(
    email: String,
    password: String
) {
    Text(loginState.email)
    Text(loginState.password)
    Button(
        onClick = Launching { LoginIntent.emit() }
    ) {
        Text("Login")
    }
}

Libraries used

  • kotlinx.coroutines
  • kotlinx.datetime
  • SQLDelight
  • Multiplatform Settings
  • Okio

GitHub

View Github