Getting accelerometer data in background using CoreMotion

Question

I'm unable to receive accelerometer data in the background, despite the seemingly correct solution per this question How Nike+ GPS on iPhone receives accelerometer updates in the background?

[_motionManager startAccelerometerUpdatesToQueue:[[NSOperationQueue alloc] init]
                                         withHandler:^(CMAccelerometerData *accelerometerData, NSError *error) {
                                             dispatch_async(dispatch_get_main_queue(), ^{
                                                 NSLog(@"perform");
                                                 [(id) self setAcceleration:accelerometerData.acceleration];
                                                 [self performSelectorOnMainThread:@selector(update) withObject:nil waitUntilDone:NO];
                                             });}];

perform is logged whenever the app is in the foreground, but whenever I exit out to background it stops running. Does anyone have any idea why this might be? I've checked "Location Updates" in Background Modes...

I've noticed it seems to work in the background if you use [NSOperationQueue mainQueue] instead of create a new queue. — leremjs, Aug 29 '17 at 18:18

score 7 · Answer 1 · answered May 20 '14 at 00:31

7

Put this code right in front of that line (after making a member variable called bgTaskID of type UIBackgroundTaskIdentifier):

UIApplication *application = [UIApplication sharedApplication];
        __weak __typeof(&*self)weakSelf = self;
        self.bgTaskID = [application beginBackgroundTaskWithExpirationHandler:^{
            __strong __typeof(&*weakSelf)strongSelf = weakSelf;

            NSLog(@"BG TASK EXPIRED!");

            if (strongSelf) {
                [application endBackgroundTask:strongSelf.bgTaskID];
                strongSelf.bgTaskID = UIBackgroundTaskInvalid;
            }
        }];

answered May 20 '14 at 00:31

fjlksahfob

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Works fine for iOS 7 for me. Did you mean iOS 8? – fjlksahfob Aug 21 '14 at 21:45
NO I mean IOS 7. I need the coreMotion Information, does this solution also works with Automotive/running/walking Information of the CoreMotion Processor in background? Is it also possible to start e.g. gps to get locations based on that information? – verklixt Aug 22 '14 at 21:51
it works for core motion. You can also use it to get GPS information. – fjlksahfob Aug 25 '14 at 18:31
You are brilliant! Works great in iOS 9.3. Solved a big problem for me – vboombatz Apr 18 '16 at 00:19

score 0 · Answer 2 · answered Mar 10 '15 at 04:08

It can be done by using CoreMotion framework. You have to import CoreMotion framework, then #import <CoreMotion/CoreMotion.h> in your appdelegate.

Here motionManager is object of CMMotionManager.

xData, yData, zData are double values to store accelerometer data.

if (motionManager ==nil) {
    motionManager= [[CMMotionManager alloc]init];
}
[motionManager startAccelerometerUpdates];

[motionManager startAccelerometerUpdatesToQueue:[NSOperationQueue mainQueue] withHandler:^(CMAccelerometerData *accelerometerData, NSError *error) {
    xData = accelerometerData.acceleration.x;
    yData = accelerometerData.acceleration.y;
    zData = accelerometerData.acceleration.z;
}];

You have to do it in - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions.

You can then use these value of xData, yData, zData where ever you want by appdelegate object, even in background.

Getting accelerometer data in background using CoreMotion

2 Answers2

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