Core Motion

作者 dpearson26998d90fd121a26无许可证1.1K 个星标收录于 2026年10月8日更新于 2026年10月8日仓库2个月前更新

Access Core Motion accelerometer, gyroscope, magnetometer, device-motion, pedometer, activity-recognition, altitude, headphone motion, batched high-frequency workout motion, and water-submersion/depth data. Use when reading device sensors, counting steps, detecting walking/running/driving/cycling, tracking altitude, building motion interactions, handling AirPods head tracking, or implementing watchOS dive/depth features.

仅含说明Software Development
AI 生成的概览

指导 Swift 开发者读取 Apple Core Motion 传感器数据，包括加速度计、陀螺仪、计步器、活动识别和高度。

功能
该技能为在 iOS 26 及更高版本、Swift 6.3 中使用 Apple Core Motion 框架提供参考指导和代码片段。内容涵盖设置要求、授权、CMMotionManager 传感器流、处理后的设备运动、CMPedometer、CMMotionActivityManager、CMAltimeter、更新间隔、常见错误和审查清单。它产出的是说明性文档，而非可执行代码。
适用场景
适用于实现或审查读取设备传感器、计步、检测步行或驾驶、追踪高度，或处理耳机与入水运动的 iOS/watchOS 功能。面向需要使用 Core Motion API 并寻求设置、授权和最佳实践指导的开发者。
运行要求
除 AI 代理外，无需脚本或运行时依赖。指导面向 Swift 6.3 和 iOS 26+，并提及 Info.plist 配置和设备传感器可用性。

CoreMotion

Read device motion, pedometer/activity, altitude, headphone, batched-workout, and submersion sensors with Core Motion. Scope: Swift 6.3, iOS 26+.

Contents

Setup

Info.plist

Add NSMotionUsageDescription to Info.plist with a user-facing string explaining why your app needs motion data. Without this key, the app crashes on first access.

xml
<key>NSMotionUsageDescription</key><string>This app uses motion data to track your activity.</string>

Authorization

Use the matching manager's authorizationStatus() or authorizationStatus property when an API exposes one (CMPedometer, CMMotionActivityManager, CMAltimeter, headphone motion, batched sensors, and submersion). Raw CMMotionManager accelerometer/gyro/device-motion streams have no explicit authorization request API; still ship the usage string and handle errors from start/update callbacks.

swift
import CoreMotion
let status = CMMotionActivityManager.authorizationStatus()switch status {case .notDetermined:    // Will prompt on first use    breakcase .authorized:    breakcase .restricted, .denied:    // Direct user to Settings    break@unknown default:    break}

CMMotionManager: Sensor Data

Create exactly one CMMotionManager per app. Multiple instances degrade sensor update rates.

swift
import CoreMotion
let motionManager = CMMotionManager()

Accelerometer Updates

swift
guard motionManager.isAccelerometerAvailable else { return }
motionManager.accelerometerUpdateInterval = 1.0 / 60.0  // 60 Hz
motionManager.startAccelerometerUpdates(to: .main) { data, error in    guard let acceleration = data?.acceleration else { return }    print("x: \(acceleration.x), y: \(acceleration.y), z: \(acceleration.z)")}
// When done:motionManager.stopAccelerometerUpdates()

Gyroscope Updates

swift
guard motionManager.isGyroAvailable else { return }
motionManager.gyroUpdateInterval = 1.0 / 60.0
motionManager.startGyroUpdates(to: .main) { data, error in    guard let rotationRate = data?.rotationRate else { return }    print("x: \(rotationRate.x), y: \(rotationRate.y), z: \(rotationRate.z)")}
motionManager.stopGyroUpdates()

Polling Pattern (Games)

For games, start updates without a handler and poll the latest sample each frame:

swift
motionManager.startAccelerometerUpdates()
// In your game loop / display link:if let data = motionManager.accelerometerData {    let tilt = data.acceleration.x    // Move player based on tilt}

Processed Device Motion

Device motion fuses accelerometer, gyroscope, and magnetometer into a single CMDeviceMotion object with attitude, user acceleration (gravity removed), rotation rate, and calibrated magnetic field.

When giving device-motion guidance, show the runtime frame check in the snippet instead of hard-coding a corrected, magnetic-north, or true-north frame. Fall back to .xArbitraryZVertical when the preferred frame is unavailable.

swift
guard motionManager.isDeviceMotionAvailable else { return }
let availableFrames = CMMotionManager.availableAttitudeReferenceFrames()let frame: CMAttitudeReferenceFrame = availableFrames.contains(.xArbitraryCorrectedZVertical)    ? .xArbitraryCorrectedZVertical    : .xArbitraryZVertical
motionManager.deviceMotionUpdateInterval = 1.0 / 60.0
motionManager.startDeviceMotionUpdates(    using: frame,    to: .main) { motion, error in    guard let motion else { return }
    let attitude = motion.attitude       // roll, pitch, yaw    let userAccel = motion.userAcceleration    let gravity = motion.gravity    let heading = motion.heading         // degrees relative to the current frame
    print("Pitch: \(attitude.pitch), Roll: \(attitude.roll)")}
motionManager.stopDeviceMotionUpdates()

Attitude Reference Frames

For simple tilt controls, use .xArbitraryZVertical or .xArbitraryCorrectedZVertical; they avoid magnetometer/location dependencies. Before requesting corrected, magnetic-north, or true-north frames, call CMMotionManager.availableAttitudeReferenceFrames() and fall back to an available frame.

FrameUse Case
.xArbitraryZVerticalDefault. Z is vertical, X arbitrary at start. Most games.
.xArbitraryCorrectedZVerticalSame as above, corrected for gyro drift over time.
.xMagneticNorthZVerticalX points to magnetic north. Requires magnetometer.
.xTrueNorthZVerticalX points to true north. Requires magnetometer + location.

Check available frames before use:

swift
let available = CMMotionManager.availableAttitudeReferenceFrames()if available.contains(.xTrueNorthZVertical) {    // Safe to use true north}

CMPedometer: Step and Distance Data

CMPedometer provides step counts, distance, pace, cadence, and floor counts.

swift
let pedometer = CMPedometer()
guard CMPedometer.isStepCountingAvailable() else { return }
// Historical querypedometer.queryPedometerData(    from: Calendar.current.startOfDay(for: Date()),    to: Date()) { data, error in    guard let data else { return }    print("Steps today: \(data.numberOfSteps)")    print("Distance: \(data.distance?.doubleValue ?? 0) meters")    print("Floors up: \(data.floorsAscended?.intValue ?? 0)")}
// Live updatespedometer.startUpdates(from: Date()) { data, error in    guard let data else { return }    print("Steps: \(data.numberOfSteps)")}
// Stop when donepedometer.stopUpdates()

Availability Checks

MethodWhat It Checks
isStepCountingAvailable()Step counter hardware
isDistanceAvailable()Distance estimation
isFloorCountingAvailable()Barometric altimeter for floors
isPaceAvailable()Pace data
isCadenceAvailable()Cadence data

CMMotionActivityManager: Activity Recognition

Detects whether the user is stationary, walking, running, cycling, or in a vehicle.

swift
let activityManager = CMMotionActivityManager()
guard CMMotionActivityManager.isActivityAvailable() else { return }
// Live activity updatesactivityManager.startActivityUpdates(to: .main) { activity in    guard let activity else { return }
    if activity.walking {        print("Walking (confidence: \(activity.confidence.rawValue))")    } else if activity.running {        print("Running")    } else if activity.automotive {        print("In vehicle")    } else if activity.cycling {        print("Cycling")    } else if activity.stationary {        print("Stationary")    }}
activityManager.stopActivityUpdates()

Historical Activity Query

swift
let yesterday = Calendar.current.date(byAdding: .day, value: -1, to: Date())!
activityManager.queryActivityStarting(    from: yesterday,    to: Date(),    to: .main) { activities, error in    guard let activities else { return }    for activity in activities {        print("\(activity.startDate): walking=\(activity.walking)")    }}

CMAltimeter: Altitude Data

Altimeter access is covered by NSMotionUsageDescription; handle denied motion access through unavailable data and update-handler errors.

swift
let altimeter = CMAltimeter()
guard CMAltimeter.isRelativeAltitudeAvailable() else { return }
altimeter.startRelativeAltitudeUpdates(to: .main) { data, error in    guard let data else { return }    print("Relative altitude: \(data.relativeAltitude) meters")    print("Pressure: \(data.pressure) kPa")}
altimeter.stopRelativeAltitudeUpdates()

Absolute altitude is altitude relative to sea level, not GPS-based altitude. First check availability. Absolute altitude is available only on supported hardware such as iPhone 12 or later and Apple Watch Series 6, Apple Watch SE, or later.

swift
guard CMAltimeter.isAbsoluteAltitudeAvailable() else { return }
altimeter.startAbsoluteAltitudeUpdates(to: .main) { data, error in    guard let data else { return }    print("Altitude: \(data.altitude)m, accuracy: \(data.accuracy)m")}
altimeter.stopAbsoluteAltitudeUpdates()

Update Intervals and Battery

IntervalHzUse CaseBattery Impact
1.0 / 10.010UI orientationLow
1.0 / 30.030Casual gamesModerate
1.0 / 60.060Action gamesHigh
1.0 / 100.0100Max rate (iPhone)Very High

Use the lowest frequency that meets your needs. Do not assume a fixed maximum sample rate across devices. For high-frequency workout motion, use CMBatchedSensorManager where supported and read its reported accelerometerDataFrequency or deviceMotionDataFrequency instead of assigning those read-only properties.

Common Mistakes

DON'T: Create multiple CMMotionManager instances

Retain one app-level CMMotionManager; competing instances can reduce update rates.

DON'T: Skip sensor availability checks

Apply the matching is...Available gate immediately before starting each sensor stream.

DON'T: Forget to stop updates

Pair every start with the matching stop in the counterpart lifecycle or task cancellation path.

DON'T: Use unnecessarily high update rates

Choose the lowest rate that meets the interaction and use the Update Intervals and Battery table as a starting point.

DON'T: Assume all CMMotionActivity properties are mutually exclusive

swift
// WRONG -- checking only one propertyif activity.walking { handleWalking() }
// CORRECT -- multiple can be true simultaneously; check confidenceif activity.walking && activity.confidence == .high {    handleWalking()} else if activity.automotive && activity.confidence != .low {    handleDriving()}

Review Checklist

  • NSMotionUsageDescription present in Info.plist with a clear explanation
  • Single CMMotionManager instance shared across the app
  • Sensor availability checked before starting updates (isAccelerometerAvailable, etc.)
  • Authorization status checked before pedometer/activity APIs
  • Update interval set to the lowest acceptable frequency
  • All start*Updates calls have matching stop*Updates in lifecycle counterparts
  • Handlers dispatched to appropriate queues (not blocking main for heavy processing)
  • CMMotionActivity.confidence checked before acting on activity type
  • Error parameters checked in update handlers
  • Device-motion snippets call CMMotionManager.availableAttitudeReferenceFrames() before requesting a specific attitude frame
  • Attitude reference frame chosen based on actual need (not defaulting to true north unnecessarily)

References

来源与署名

来源：dpearson2699/swift-ios-skills位于skills/core-motion提交8d90fd1

许可证： 无许可证

内容归原作者所有。SourceWeft 从公开仓库中收录这些内容。

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