tila

Tila is a Finnish word meaning state (among other things).

Purpose

flowchart TD
;
    C(app state) -->|derive| D(state)
    A(composable function) -->|send event| B(event handler)
    D -->|inject MutableState| A
    B -->|call| E(business logic)
    E -->|send event| B
    B -->|update| C

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Tila provides a straightforward way to handle a state in an application. It enables to extract click handlers away from UI code making it simple. Also, it makes Composable functions truly transform their state from data.

Benefits

• Simplify UI code
• Make click handlers testable
• Pass any number of parameters to Composable functions easily
• Make composable functions testable (detached from business logic)
• Make the app testable without UI (drive tests by calling click handlers, not through UI)

Principles

• Not tied to Android/OS/ViewModel/MainActivity (Compose Multiplatform's MutableState dependency exists)
• App data and ui state/data are separated
• Easy to inject a new observed state
• Extract click handlers from UI code
• Easy to preview composable functions with any app data
• Event handlers (click handlers) work with app data and their arguments and produce modified app data
• Click handlers can be tested separately (pure functions)
• Derivatives can be tested separately (pure functions)
• Testable

Getting started

See the complete example of an Android app using tila at https://github.com/pmpuro/TilaAndroidExample.

Specify dependency

TBD

Create initial app data

private fun createInitialAppData() = mapOf(Data.counter to 100)

private val machine = createMachine(data = createInitialAppData()) {
    registerEventHandlers()
    registerDerivatives()
}

Inject states and create events

Column {
    val time by remember { machine.injectState<String>(State.timeString) }
    val counter by remember { machine.injectState<Int>(State.counterValue) }
    Greeting("Android")
    Text(text = time)
    Text(text = "counter = $counter")
    Button(onClick = machine.createEvent(Events.click)) {
        Text(text = "Press here")
    }
}

Create and register event handlers

registerEventHandler(Ids.Events.click) { appData, _ ->
    val counter = appData.accessData<Int>(Ids.Data.counter)
    val newValue = counter + 1
    mapOf(Ids.Data.counter to newValue)
}

Create and register derivatives

registerDerivative { appData ->
    val now = appData.accessDataOrNull<String>(Ids.Data.time) ?: "not available yet"
    mapOf(Ids.State.timeString to "Time now is $now")
}