CMAltimeter callback never fires - ios

Question

Using my 6+ I've been trying to read the relative altitude and pressure using CoreMotion's new CMAltimeter. However the callback is never firing. I have a very similar setup which instead uses the accelerometers, gyros, and magnetometers. They all seem to work fine.
Was wondering if anyone out there has managed to get a reading?
- (void)viewDidLoad {
[super viewDidLoad];
if([CMAltimeter isRelativeAltitudeAvailable]){
CMAltimeter *altimeterManager = [[CMAltimeter alloc]init];
[altimeterManager startRelativeAltitudeUpdatesToQueue:[NSOperationQueue mainQueue] withHandler:^(CMAltitudeData *altitudeData, NSError *error) {
// This never fires.
NSString *data = [NSString stringWithFormat:#"Altitude: %f %f", altitudeData.relativeAltitude.floatValue, altitudeData.pressure.floatValue];
NSLog(#"%#", data);
self.altimeterLabel.text = data;
}];
NSLog(#"Started altimeter");
self.altimeterLabel.text = #"-\n-";
} else {
NSLog(#"Altimeter not available");
}
}
I've tried taking this on a quick walk, but there's only one story of altitude to lose/gain around here.

Answer 1

I'm pretty embarrased to answer my own question with such a huge oversight.
In the original post I had the CMAltimiter declared in the scope of viewDidLoad, thus it goes out of scope and is deallocated. I moved it to be an iVar and the callback now fires.
#import "ViewController.h"
#import CoreMotion;
#interface ViewController ()
#property (nonatomic, strong) CMAltimeter *altimeterManager;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
if([CMAltimeter isRelativeAltitudeAvailable]){
self.altimeterManager = [[CMAltimeter alloc]init];
[self.altimeterManager startRelativeAltitudeUpdatesToQueue:[NSOperationQueue mainQueue] withHandler:^(CMAltitudeData *altitudeData, NSError *error) {
// This now fires properly
NSString *data = [NSString stringWithFormat:#"Altitude: %f %f", altitudeData.relativeAltitude.floatValue, altitudeData.pressure.floatValue];
NSLog(#"%#", data);
self.altimeterLabel.text = data;
}];
NSLog(#"Started altimeter");
self.altimeterLabel.text = #"-\n-";
} else {
NSLog(#"Altimeter not available");
}
}

Answer 2

You need to call [altimeterManager stopRelativeAltitudeUpdates]; for the references to be released to the dispatch queue.