Using MetricKit

Pre-release • Release date: 28 January 2025 • 3 min read • MetricKit Swift

In this post, I will show you how to use MetricKit to collect and analyze performance data from your app.

What is MetricKit?

MetricKit is a framework introduced in iOS 13 that allows you to collect and analyze performance data from your app.
It provides a set of APIs to access metrics such as CPU usage, memory usage, disk I/O, and network I/O.
You can use this data to identify performance bottlenecks, optimize your app, and improve the user experience.

What metrics can you collect?

MetricKit provides APIs to collect the following metrics:

Diagnostics for crashes
Hangs
Energy
Disk writes

How to use MetricKit?

To use MetricKit in your app, you need to follow these steps:

Step 1: Import MetricKit

import MetricKit

Step 2: Register for metric updates

To receive metric updates, you need to create a class that conforms to the MXMetricManagerSubscriber protocol and register your class with the MXMetricManager singleton object in your app's main entry point.

@main
struct DinnerConnectApp: App {
    private var metrics = MetricSubscriber()

    var body: some Scene {
        WindowGroup {
            MyAppView()
                .onAppear {
                    MXMetricManager.shared.add(metrics)
                }
        }
    }
}

Step 3: Implement the MetricSubscriber protocol

We create a MetricSubscriber class that conforms to the MXMetricManagerSubscriber protocol to receive metric payloads.

class MetricSubscriber: NSObject, MXMetricManagerSubscriber {
    func didReceive(_ payloads: [MXMetricPayload]) {
        print("didReceive MXMetricPayload")
        guard let firstPayload = payloads.first else { return }

        if let jsonString = String(
            data: firstPayload.jsonRepresentation(), 
            encoding: .utf8
        ) {
            print(jsonString)
        } else {
            print("Failed to encode")
        }
    }

    func didReceive(_ payloads: [MXDiagnosticPayload]) {
        print("didReceive MXDiagnosticPayload")
        guard let firstPayload = payloads.first else { return }

        if let jsonString = String(
            data: firstPayload.jsonRepresentation(), 
            encoding: .utf8
        ) {
            print(jsonString)
        } else {
            print("Failed to encode")
        }
    }
}

Debugging MetricKit

MetricKit will only work on a real device, not on the simulator.
To send a metric payload to your app, you can go to Debug > Simulate MetricKit Payloads in Xcode.

References/resources:

Understanding Package.swift • 13 minutes reading time.
SwiftLeeds 2024, Day 1 • 11 minutes reading time.
Appril Festival 2024 • 7 minutes reading time.

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