metrickit

MetricKit Collect aggregated performance metrics and crash diagnostics from production devices using MetricKit. The framework delivers daily metric payloads (CPU, memory, launch time, hang rate, animation hitches, network usage) and immediate diagnostic payloads (crashes, hangs, disk-write exceptions) with full call-stack trees for triage. Contents Subscriber Setup Receiving Metric Payloads Receiving Diagnostic Payloads Key Metrics Call Stack Trees Custom Signpost Metrics Exporting and Uploading Payloads Extended Launch Measurement Xcode Organizer Integration Common Mistakes Review Checklist References Subscriber Setup Register a subscriber as early as possible — ideally in application(:didFinishLaunchingWithOptions:) or App.init . MetricKit starts accumulating reports after the first access to MXMetricManager.shared . import MetricKit final class MetricsSubscriber : NSObject , MXMetricManagerSubscriber { static let shared = MetricsSubscriber ( ) func subscribe ( ) { MXMetricManager . shared . add ( self ) } func unsubscribe ( ) { MXMetricManager . shared . remove ( self ) } func didReceive ( _ payloads : [ MXMetricPayload ] ) { // Handle daily metrics } func didReceive ( _ payloads : [ MXDiagnosticPayload ] ) { // Handle diagnostics (crashes, hangs, disk writes) } } UIKit Registration func application ( _ application : UIApplication , didFinishLaunchingWithOptions launchOptions : [ UIApplication . LaunchOptionsKey : Any ] ? ) -> Bool { MetricsSubscriber . shared . subscribe ( ) return true } SwiftUI Registration @main struct MyApp : App { init ( ) { MetricsSubscriber . shared . subscribe ( ) } var body : some Scene { WindowGroup { ContentView ( ) } } } Receiving Metric Payloads MXMetricPayload arrives approximately once per 24 hours containing aggregated metrics. The array may contain multiple payloads if prior deliveries were missed. func didReceive ( _ payloads : [ MXMetricPayload ] ) { for payload in payloads { let begin = payload . timeStampBegin let end = payload . timeStampEnd let version = payload . latestApplicationVersion // Persist raw JSON before processing let jsonData = payload . jsonRepresentation ( ) persistPayload ( jsonData , from : begin , to : end ) processMetrics ( payload ) } } Availability : MXMetricPayload — iOS 13.0+, macOS 10.15+, visionOS 1.0+ Receiving Diagnostic Payloads MXDiagnosticPayload delivers crash, hang, CPU exception, disk-write, and app-launch diagnostics. On iOS 15+ and macOS 12+, diagnostics arrive immediately rather than bundled with the daily report. func didReceive ( _ payloads : [ MXDiagnosticPayload ] ) { for payload in payloads { let jsonData = payload . jsonRepresentation ( ) persistPayload ( jsonData ) if let crashes = payload . crashDiagnostics { for crash in crashes { handleCrash ( crash ) } } if let hangs = payload . hangDiagnostics { for hang in hangs { handleHang ( hang ) } } if let diskWrites = payload . diskWriteExceptionDiagnostics { for diskWrite in diskWrites { handleDiskWrite ( diskWrite ) } } if let cpuExceptions = payload . cpuExceptionDiagnostics { for cpuException in cpuExceptions { handleCPUException ( cpuException ) } } if let launchDiags = payload . appLaunchDiagnostics { for launchDiag in launchDiags { handleSlowLaunch ( launchDiag ) } } } } Availability : MXDiagnosticPayload — iOS 14.0+, macOS 12.0+, visionOS 1.0+ Key Metrics Launch Time — MXAppLaunchMetric if let launch = payload . applicationLaunchMetrics { let firstDraw = launch . histogrammedTimeToFirstDraw let optimized = launch . histogrammedOptimizedTimeToFirstDraw let resume = launch . histogrammedApplicationResumeTime let extended = launch . histogrammedExtendedLaunch } Run Time — MXAppRunTimeMetric if let runTime = payload . applicationTimeMetrics { let fg = runTime . cumulativeForegroundTime // Measurement let bg = runTime . cumulativeBackgroundTime let bgAudio = runTime . cumulativeBackgroundAudioTime let bgLocation = runTime . cumulativeBackgroundLocationTime } CPU, Memory, and Responsiveness if let cpu = payload . cpuMetrics { let cpuTime = cpu . cumulativeCPUTime // Measurement } if let memory = payload . memoryMetrics { let peakMemory = memory . peakMemoryUsage // Measurement } if let responsiveness = payload . applicationResponsivenessMetrics { let hangTime = responsiveness . histogrammedApplicationHangTime } if let animation = payload . animationMetrics { let scrollHitchRate = animation . scrollHitchTimeRatio // Measurement } Network and Cellular if let network = payload . networkTransferMetrics { let wifiUp = network . cumulativeWifiUpload // Measurement let wifiDown = network . cumulativeWifiDownload let cellUp = network . cumulativeCellularUpload let cellDown = network . cumulativeCellularDownload } App Exit Metrics if let exits = payload . applicationExitMetrics { let fg = exits . foregroundExitData let bg = exits . backgroundExitData // Inspect normal, abnormal, watchdog, memory, etc. } Call Stack Trees MXCallStackTree is attached to each diagnostic. Use jsonRepresentation() to extract frame data, then symbolicate with atos or by uploading dSYMs to your analytics service. See references/metrickit-patterns.md for crash/hang handling code and JSON structure details. Availability : MXCallStackTree — iOS 14.0+, macOS 12.0+, visionOS 1.0+ Custom Signpost Metrics Use mxSignpost with a MetricKit log handle to capture custom performance intervals. These appear in the daily MXMetricPayload under signpostMetrics . let metricLog = MXMetricManager . makeLogHandle ( category : "Networking" ) See references/metrickit-patterns.md for signpost emission patterns and reading custom metrics from payloads. Exporting and Uploading Payloads Both payload types provide jsonRepresentation() for serialization. Always persist raw JSON to disk before processing — the system delivers each payload once. Use pastPayloads and pastDiagnosticPayloads on launch to recover missed deliveries. See references/metrickit-patterns.md for export code and past payload retrieval. Extended Launch Measurement Track post-first-draw setup work as part of the launch metric: let taskID = MXLaunchTaskID ( "com.example.app.loadDatabase" ) MXMetricManager . shared . extendLaunchMeasurement ( forTaskID : taskID ) await database . load ( ) MXMetricManager . shared . finishExtendedLaunchMeasurement ( forTaskID : taskID ) Extended launch times appear under histogrammedExtendedLaunch in MXAppLaunchMetric . Xcode Organizer Integration Xcode Organizer shows aggregated MetricKit data across opted-in users. Use it for trend analysis alongside on-device collection routed to your own backend. See references/metrickit-patterns.md for Organizer tab details. Common Mistakes DON'T: Subscribe to MXMetricManager too late The system may deliver pending payloads shortly after launch. Subscribing late (e.g., in a view controller) risks missing them entirely. // WRONG — subscribing in a view controller override func viewDidLoad ( ) { super . viewDidLoad ( ) MXMetricManager . shared . add ( self ) } // CORRECT — subscribe in application(:didFinishLaunchingWithOptions:) func application ( _ application : UIApplication , didFinishLaunchingWithOptions opts : [ UIApplication . LaunchOptionsKey : Any ] ? ) -> Bool { MXMetricManager . shared . add ( metricsSubscriber ) return true } DON'T: Ignore MXDiagnosticPayload Only handling MXMetricPayload means you miss crash, hang, and disk-write diagnostics — the most actionable data MetricKit provides. // WRONG — only implementing metric callback func didReceive ( _ payloads : [ MXMetricPayload ] ) { / ... / } // CORRECT — implement both callbacks func didReceive ( _ payloads : [ MXMetricPayload ] ) { / ... / } func didReceive ( _ payloads : [ MXDiagnosticPayload ] ) { / ... / } DON'T: Process payloads without persisting first The system delivers each payload once. If your subscriber crashes during processing, the data is lost permanently. // WRONG — process inline, crash loses data func didReceive ( _ payloads : [ MXDiagnosticPayload ] ) { for p in payloads { riskyProcessing ( p ) // If this crashes, payload is gone } } // CORRECT — persist raw JSON first, then process func didReceive ( _ payloads : [ MXDiagnosticPayload ] ) { for p in payloads { let json = p . jsonRepresentation ( ) try ? json . write ( to : localCacheURL ( ) ) // Safe on disk Task . detached { self . processAsync ( json ) } } } DON'T: Do heavy work synchronously in didReceive The callback runs on an arbitrary thread. Blocking it with heavy processing or synchronous network calls delays delivery of subsequent payloads. // WRONG — synchronous upload in callback func didReceive ( _ payloads : [ MXMetricPayload ] ) { for p in payloads { let data = p . jsonRepresentation ( ) URLSession . shared . uploadTask ( with : request , from : data ) . resume ( ) // sync wait } } // CORRECT — persist and dispatch async func didReceive ( _ payloads : [ MXMetricPayload ] ) { for p in payloads { let json = p . jsonRepresentation ( ) persistLocally ( json ) Task . detached ( priority : . utility ) { await self . uploadToBackend ( json ) } } } DON'T: Expect immediate data in development MetricKit aggregates data over 24-hour windows. Payloads do not arrive immediately after instrumenting. Use Xcode Organizer or simulated payloads for faster iteration during development. Review Checklist MXMetricManager.shared.add(subscriber) called in application(:didFinishLaunchingWithOptions:) or App.init Subscriber conforms to MXMetricManagerSubscriber and inherits NSObject Both didReceive(: [MXMetricPayload]) and didReceive(_: [MXDiagnosticPayload]) implemented Raw jsonRepresentation() persisted to disk before processing Heavy processing dispatched asynchronously off the callback thread MXCallStackTree JSON uploaded with dSYMs for symbolication Custom signpost metrics limited to critical code paths pastPayloads and pastDiagnosticPayloads checked on launch for missed deliveries Extended launch tasks call both extendLaunchMeasurement and finishExtendedLaunchMeasurement Analytics backend accepts and stores MetricKit JSON format Xcode Organizer reviewed for regression trends alongside on-device data References Extended patterns: references/metrickit-patterns.md MetricKit framework MXMetricManager MXMetricManagerSubscriber MXMetricPayload MXDiagnosticPayload