(0 Documentation
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`Language: Swift Y
`
`API changes: None
`
`Core Motion / Getting raw accelerometer events
`
`Article
`
`Getting raw accelerometer events
`
`Retrieve data from the onboard accelerometers.
`
`Overview
`
`An accelerometer measures changesin velocity along one axis. All iOS devices have a three-axis
`accelerometer, which delivers acceleration values in each of the three axes shown in the next
`illustration. The values reported by the accelerometers are measured in increments of the
`gravitational acceleration, with the value 1.@ representing an acceleration of 9.8 meters per
`second (per second) in the given direction. Acceleration values may be positive or negative
`depending on the direction of the acceleration.
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`+Y
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`Page 1 of 6
`Page 1 of 6
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`HAPTIC EX2020
`HAPTIC EX2020
`
`
`
`Language: Swift Y
`
`API changes: None
`
`Core Motion / Getting raw accelerometer events
`
`Article
`
`Getting raw accelerometer events
`
`Retrieve data from the onboard accelerometers.
`
`Overview
`
`An accelerometer measures changesin velocity along one axis. All iOS devices have a three-axis
`accelerometer, which delivers acceleration values in each of the three axes shown in the next
`illustration. The values reported by the accelerometers are measured in increments of the
`gravitational acceleration, with the value 1.@ representing an acceleration of 9.8 meters per
`second (per second) in the given direction. Acceleration values may be positive or negative
`depending on the direction of the acceleration.
`
`+Y
`
`fh
`
`+Z
`
`SN
`
`+X
`
`Page 1 of 6
`Page 1 of 6
`
`HAPTIC EX2020
`HAPTIC EX2020
`
`
`
`v
`
`-Y
`
`You access the raw accelerometer data using the classes of the Core Motion framework.
`Specifically, the CMMotionManager class provides the interfaces for enabling the accelerometer
`hardware. When enabling the hardware, choose the interfaces that are best suited for your app.
`You can pull the accelerometer data only when you need it, or you can ask the framework to push
`updates to your app at regular intervals. Each technique involves different configuration steps and
`has a different use case.
`
`Important
`
`If your app relies on the presence of accelerometer hardware, configure the UIRequired
`DeviceCapabili ties key of its Info. plist file with the accelerometer value. For
`more information about the meaning of this key, see Information Pro12erty List Key Reference.
`
`For information about the coordinate axes of different device types, see CMMotionManager.
`
`Check for the availability of accelerometer data
`
`Accelerometer data might be unavailable for a variety of reasons, so verify that the data is available
`before you try to obtain it. Check the value of the isAccelerometerAvailable property of
`CMMotionManager and make sure it's true. If it's false, starting updates doesn't deliver any
`data to your app.
`
`Important
`
`In visionOS, accelerometer data is available only when your app has an open immersive space.
`For more information, see ImmersiveSi:iace.
`
`Get accelerometer data only when you need it
`
`For apps that process accelerometer data on their own schedule, such as games, use the st a rt
`AccelerometerUpdates () method of CMMotionManager to start the delivery of
`accelerometer data. When you call this method, the system enables the accelerometer hardware
`and begins updating the accelerometerData property of your CMMotionManager object.
`However, the system does not notify you when it updates that property. You must explicitly check
`the value of the property when you need the accelerometer data.
`
`Page 2 of 6
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`
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`Before you start the delivery of accelerometer updates, specify an update frequency by assigning
`a value to the accelerometerUpdateinterval property. The maximum frequency at which
`you can request updates is hardware-dependent but is usually at least 100 Hz. If you request a
`frequency that is greater than what the hardware supports, Core Motion uses the supported
`maximum instead.
`
`The example below shows a method that configures accelerometer updates to occur 50 times per
`second. The method then configures a timer to fetch those updates at the same frequency and do
`something with the data. You could configure the timer to fire at a lower frequency, but doing so
`would waste power by causing the hardware to generate more updates than were actually used.
`
`let motion= CMMotionManager ()
`
`func startAccelerometers () {
`II Make sure the accelerometer hardware is available.
`if self .motion.isAccelerometerAvailable {
`self .motion.accelerometerUpdateinterval = 1.0 I 50.0
`self .motion.startAccelerometerUpdates()
`
`II 50 Hz
`
`II Configure a timer to fetch the data.
`self .timer= Timer (fire: Date (), interval: (1.0150.0 ),
`repeats: true , block: { (timer) in
`II Get the accelerometer data.
`if let data= self .motion.accelerometerData {
`let x = data.acceleration.x
`let y = data.acceleration.y
`let z = data.acceleration.z
`
`II Use the accelerometer data 1n your app.
`
`}
`
`})
`
`II Add the timer to the current run loop.
`Runloop .current.add( self .timer!, forMode:
`
`.defaultRunloopMode)
`
`}
`
`}
`
`Process a steady stream of accelerometer data
`
`Page 3 of 6
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`
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`When you want to capture all of the incoming accelerometer data, perhaps so you can analyze it
`for movement patterns, use the startAccelerometerUpdates (to: wi thHandler: ) method
`of CMMotionManager. This method pushes each new set of accelerometer values to your app by
`executing your handler block on the specified queue. The queueing of these blocks ensures that
`your app receives all of the accelerometer data, even if your app becomes busy and is unable to
`process updates for a brief period of time.
`
`Before you start the delivery of accelerometer updates, specify an update frequency by assigning
`a value to the accelerometerUpdateinterval property. The maximum frequency at which
`you can request updates is hardware-dependent but is usually at least 100 Hz. If you request a
`frequency that is greater than what the hardware supports, Core Motion uses the supported
`maximum instead.
`
`The following example shows a method from the MotionGraphs sample code project, which you
`can examine for more context. The app displays a real-time graph of accelerometer data. The user
`configures the update frequency for the accelerometers using a slider, the changing of which
`results in a call to the startUpdatesWi thSliderValue: method shown in the example. This
`method restarts the accelerometer updates with the new frequency. Each time a new sample is
`received, the specified block is queued on the main thread. That block updates the app's graph
`view and labels with the new accelerometer values.
`
`Page 4 of 6
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`
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`static canst NSTimeinterval accelerometerMin = 0.01 ;
`(void )startUpdatesWithSliderValue:( int )sliderValue {
`-
`II Determine the update interval.
`NSTimeinterval delta= 0.005 ;
`NSTimeinterval updateinterval = accelerometerMin +delta* sliderValue;
`II Create a CMMotionManager object.
`CMMotionManager *mManager = [(APLAppDelegate *)
`[[ UIApplication sharedApplication] delegate] sharedManager];
`APLAccelerometerGraphViewController * __ weak weakSelf = self ;
`II Check whether the accelerometer is available.
`if ([mManager isAccelerometerAvailable] == YES ) {
`II Assign the update interval to the motion manager.
`[mManager setAccelerometerUpdateinterval:updateinterval];
`[mManager startAccelerometerUpdatesToQueue:[ NSOperationQueue mainQueue]
`withHandler:A( CMAccelerometerData *accelerometerData, NSError *error)
`[weakSelf.graphView addX:accelerometerData.acceleration.x
`y:accelerometerData.acceleration.y
`z:accelerometerData.acceleration.z];
`[weakSelf setlabelValueX:accelerometerData.acceleration.x
`y:accelerometerData.acceleration.y
`z:accelerometerData.acceleration.z];
`
`} ] ;
`
`}
`self .updateintervalLabel.text = [NSString stringWithFormat: @"%f" , updateintervalJ
`
`}
`-
`
`(void )stopUpdates {
`CMMotionManager *mManager = [(APLAppDelegate *)
`[[ UIApplication sharedApplication] delegate] sharedManager];
`if ([mManager isAccelerometerActiveJ == YES ) {
`[mManager stopAccelerometerUpdatesJ;
`
`}
`
`}
`
`See Also
`
`Accelerometers
`
`Page 5 of 6
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`
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`class CMAccelerometerData
`
`A data sample from the device's three accelerometers.
`
`class CMRecordedAccelerometerData
`A single piece of accelerometer data that was recorded by the device.
`
`class CMSensorRecorder
`An object that gathers and retrieves accelerometer data from a device.
`
`class CMSensorDataList
`A list of the accelerometer data recorded by the system.
`
`Page 6 of 6
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