Question

I want to store the continuously updated values returned by the locationManager:didUpdateHeading: method in either a global int or a property int, so that other functions of the MotionHandler class can use it. However, this delegate method doesn’t seem to be able to store its values globally but only locally. Why is that? Is it because it’s not an actual MotionHandler method? How can I work around this problem? Thank you for your help.

MotionHandler.m

#import "MotionHandler.h"

@interface MotionHandler()
{
    CLLocationManager *locationManager;
    int degrees; // the global in question..
}
@end

@implementation MotionHandler

-(void) startCompassUpdates
{
    locationManager =[[CLLocationManager alloc] init];
    locationManager.delegate=self;
    [locationManager startUpdatingHeading];
}

-(void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
    // This is working, a new value is stored in "degrees" & logged on the console after each update. However it only seems to be updating "degrees" locally..
    degrees = (int)locationManager.heading.magneticHeading;
    NSLog(@"from delegate method: %i", degrees); 
}

-(int) showDegrees
{
    return degrees; //  This is not working. Whenever I call this method, "degrees" is always zero. Why isn't this global being updated by the previous method ?
}

TheViewController.m

//...

- (void)viewDidLoad
{
    [super viewDidLoad];

    currentMotionHandler = [[MotionHandler alloc] init];

    [currentMotionHandler startCompassUpdates];

    while(1==1)
    {
        NSLog(@"from showDegrees method: %i",[currentMotionHandler showDegrees]); // this just keeps returning zero..
    }
}
//...

Answer 1

As per OP request, I have transferred my comments to an answer:

You need to stop using while loop to get constant feedback of the changing value. As Cocoa Touch is an event-based system you can’t hijack its run loop by creating an infinite loop in this way. Even outside of an event-based system, using such a tight loop would hurt performance and give little gain.

If you want continuous update (or something that appears to be continuous) you can:

1. Use a timer to call a method every X milliseconds (see Apple Guide).
2. Use a background thread (see Apple Guide).

I would prefer to use the timer approach as that has the lowest overhead and runs the method in the same thread as the rest of the UI, avoiding any possible threading issue.