MetricKit Modern Swift API

−import UIKit
+import SwiftUI
 import MetricKit
 
−// MARK: - Old delegate-based MetricKit (pre-iOS 27)
−class LegacyPerformanceMonitor: NSObject, MXMetricManagerSubscriber {
−    static let shared = LegacyPerformanceMonitor()
−    private let manager = MXMetricManager.shared
+// MARK: - Metric collection service
+actor PerformanceMonitor {
+    static let shared = PerformanceMonitor()
+    private let manager = MetricManager()
 
−    func start() {
−        manager.add(self)
+    func startMonitoring() async {
+        async let _ = collectMetrics()
+        async let _ = collectDiagnostics()
     }
 
−    // Called once per day with an array of payloads
−    func didReceive(_ payloads: [MXMetricPayload]) {
−        for payload in payloads {
−            // Encode entire payload to JSON
−            print("[MetricKit] Payload: \(payload.jsonRepresentation())")
+    private func collectMetrics() async {
+        for await report in manager.metricReports {
+            // MetricReports are Codable — send to your analytics server
+            if let data = try? JSONEncoder().encode(report),
+               let json = String(data: data, encoding: .utf8) {
+                print("[MetricKit] Report JSON: \(json.prefix(200))")
+            }
 
−            // Access memory metrics directly off the payload
−            if let mem = payload.memoryMetrics {
−                print("[MetricKit] Peak memory: \(mem.peakMemoryUsage)")
+            // Inspect specific intervals and metric groups
+            for entry in report.intervalEntries {
+                let memoryMetrics = entry.metrics.filter { $0.group == .memory }
+                for metric in memoryMetrics {
+                    switch metric {
+                    case .peakMemory(let measurement):
+                        print("[MetricKit] Peak memory: \(measurement)")
+                    default:
+                        break
+                    }
+                }
             }
         }
     }
 
−    // Called immediately when a diagnostic event occurs
−    func didReceive(_ payloads: [MXDiagnosticPayload]) {
−        for payload in payloads {
−            for crash in payload.crashDiagnostics ?? [] {
−                print("[MetricKit] Crash signal: \(crash.signal ?? -1)")
−                print("[MetricKit] Backtrace: \(crash.callStackTree)")
+    private func collectDiagnostics() async {
+        for await report in manager.diagnosticReports {
+            // DiagnosticReports are also Codable
+            switch report {
+            case .crash(let crash):
+                print("[MetricKit] Crash reason: \(crash.reason)")
+                print("[MetricKit] Termination category: \(crash.terminationCategory)")
+                for frame in crash.backtrace.frames {
+                    print("  \(frame)")
+                }
+            case .hang(let hang):
+                print("[MetricKit] Hang duration: \(hang.duration)")
+            case .memoryException(let mem):
+                print("[MetricKit] Memory exception — limit: \(mem.memoryLimit)")
+            default:
+                break
             }
−            for hang in payload.hangDiagnostics ?? [] {
−                print("[MetricKit] Hang duration: \(hang.hangDuration)")
−            }
         }
     }
 }
 
−// MARK: - AppDelegate wiring
−@UIApplicationMain
−class AppDelegate: UIResponder, UIApplicationDelegate {
−    func application(_ application: UIApplication,
−                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
−        LegacyPerformanceMonitor.shared.start()
−        return true
+// MARK: - App entry point
+@main
+struct MetricKitDemoApp: App {
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+                .task {
+                    // Start at launch on a detached task to avoid blocking the main actor
+                    await Task.detached(priority: .background) {
+                        await PerformanceMonitor.shared.startMonitoring()
+                    }.value
+                }
+        }
     }
+}
+
+struct ContentView: View {
+    var body: some View {
+        Text("Monitoring performance with MetricKit")
+            .padding()
+    }
 }