iOS

ActivityKit is Swift-only, so the Kotlin manager talks to a small Swift bridge. Three pieces:

1. Swift package (app and widget extension)

Add swift/HaloKMP from the repository as a local package and link it from both targets. It provides:

• HaloActivityAttributes — the single ActivityAttributes type ActivityKit uses to match an activity to its widget. Never copy or re-declare it; a duplicate type means the activity starts but nothing renders.
• HaloKit — the ActivityKit calls.
• HaloActivityWidget — a default Lock Screen + Dynamic Island UI.

2. Widget extension

import HaloKMP
import SwiftUI
import WidgetKit
 
@main
struct MyWidgets: WidgetBundle {
    var body: some Widget {
        HaloActivityWidget()
    }
}

Add NSSupportsLiveActivities = YES to the app’s Info.plist. The extension’s Info.plist needs NSExtensionPointIdentifier = com.apple.widgetkit-extension. See sample/composeApp/iosApp/project.yml for a complete xcodegen definition.

For a custom look, write your own ActivityConfiguration(for: HaloActivityAttributes.self) and read context.state (title, subtitle, timerRange, progressFraction, values).

3. Bridge file (app target only)

Copy swift/HaloBridge.swift into the app target, change import ComposeApp to your Kotlin framework’s name, and register it at launch:

@main
struct MyApp: App {
    init() { Halo.shared.register(bridge: HaloBridge()) }
    // ...
}

Export the library from the framework so Swift sees LiveActivityBridge and LiveActivities:

listOf(iosArm64(), iosSimulatorArm64()).forEach {
    it.binaries.framework {
        baseName = "ComposeApp"
        export(project(":halo"))
    }
}
// commonMain: api(project(":halo"))

Link the Kotlin framework exactly once; a second copy has its own empty bridge registry.

Behaviour

• Floor is iOS 16.2. isSupported is false until the bridge is registered.
• authorization() is Denied when ActivityAuthorizationInfo().areActivitiesEnabled is false.
• The system ends activities after eight hours; they surface as Expired.
• staleAtEpochMillis becomes ActivityContent.staleDate; the default widget dims stale content.
• Payloads over about 4 KB are refused by ActivityKit; the library caps encoded requests at 3 KB.