Watch Appとは何か、Apple WatchとWear OS向け開発

import SwiftUI
import HealthKit

// 心拍数データモデル
struct HeartRateData: Identifiable {
    let id = UUID()
    let bpm: Double
    let date: Date
}

// HealthKit用ViewModel
@Observable
final class HealthViewModel {
    private let healthStore = HKHealthStore()
    var currentHeartRate: Double = 0
    var isAuthorized: Bool = false

    func requestAuthorization() {
        guard let heartRateType = HKQuantityType.quantityType(forIdentifier: .heartRate)
        else { return }
        let types = Set([heartRateType])
        healthStore.requestAuthorization(toShare: nil, read: types) { success, _ in
            Task { @MainActor in
                self.isAuthorized = success
                if success { self.startHeartRateQuery() }
            }
        }
    }

    func startHeartRateQuery() {
        guard let heartRateType = HKQuantityType.quantityType(forIdentifier: .heartRate)
        else { return }
        let query = HKObserverQuery(
            sampleType: heartRateType, predicate: nil
        ) { [weak self] _, _, _ in
            self?.fetchLatestHeartRate()
        }
        healthStore.execute(query)
    }

    private func fetchLatestHeartRate() {
        guard let heartRateType = HKQuantityType.quantityType(forIdentifier: .heartRate)
        else { return }
        let sort = NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: false)
        let query = HKSampleQuery(
            sampleType: heartRateType, predicate: nil,
            limit: 1, sortDescriptors: [sort]
        ) { _, samples, _ in
            guard let sample = samples?.first as? HKQuantitySample else { return }
            let bpm = sample.quantity.doubleValue(for: HKUnit.count().unitDivided(by: .minute()))
            Task { @MainActor in
                self.currentHeartRate = bpm
            }
        }
        healthStore.execute(query)
    }
}

// メイン画面
struct HeartRateView: View {
    @State private var viewModel = HealthViewModel()

    var body: some View {
        VStack {
            Image(systemName: "heart.fill")
                .foregroundColor(.red)
                .font(.largeTitle)

            Text("\(Int(viewModel.currentHeartRate))")
                .font(.system(size: 60, weight: .bold, design: .rounded))
                .foregroundColor(.red)

            Text("BPM")
                .font(.caption)
                .foregroundColor(.secondary)
        }
        .padding()
        .onAppear(perform: viewModel.requestAuthorization)
    }
}

// MainActivity.kt
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.*
import androidx.wear.compose.material.*
import androidx.wear.compose.foundation.arc.BasicArcParams
import com.google.android.horologist.health.HealthService

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            WearAppTheme {
                HeartRateScreen()
            }
        }
    }
}

@Composable
fun HeartRateScreen() {
    var heartRate by remember { mutableIntStateOf(0) }
    var isConnected by remember { mutableStateOf(false) }

    LaunchedEffect(Unit) {
        // HealthService — センサーアクセス用API
        val healthService = HealthService()
        healthService.connect().onSuccess {
            isConnected = true
        }
    }

    Scaffold(
        timeText = { TimeText() },
        vignette = { Vignette(vignettePosition = VignettePosition.TopAndBottom) }
    ) {
        Column(
            modifier = Modifier
                .fillMaxSize()
                .scrollable(state = ScrollState),
            horizontalAlignment = Alignment.CenterHorizontally,
            verticalArrangement = Arrangement.Center
        ) {
            Icon(
                imageVector = Icons.Filled.Favorite,
                contentDescription = "心拍数",
                modifier = Modifier.size(40.dp),
                tint = MaterialTheme.colors.error
            )

            Text(
                text = heartRate.toString(),
                style = MaterialTheme.typography.display1
            )
            Text(
                text = "BPM",
                style = MaterialTheme.typography.caption2
            )
        }
    }
}