Question

@interface Tester()
{
    int currentAccelerationOnYaxis;
}    
@end

@implementation Tester

-(void) test
{
    CMMotionManager *motionManager = [[CMMotionManager alloc] init];
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           currentAccelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
    while(1==1)
    {
        NSLog(@"current acceleration is: %f", currentAccelerationOnYaxis);
    }
}
@end

I then execute the above method on a background thread like this :
[myTester performSelectorInBackground:@selector(test) withObject:nil];

and it works fine.

However, the following configuration is not working and I can’t figure out why :

@implementation MotionHandler

@synthesize accelerationOnYaxis; // this is an int property of the MotionHandler class

-(void) startAccelerationUpdates
{
    CMMotionManager *motionManager = [[CMMotionManager alloc] init];
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           self.accelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
}

@implementation Tester

-(id)init
{
    //...
    currentMotionHandler = [[MotionHandler alloc] init];
}
-(void) test
{
    [currentMotionHandler startAccelerationUpdates];
    while(1==1)
    {
        NSLog(@"current acceleration is: %f", currentMotionHandler.accelerationOnYaxis);
    }
}
@end

I then execute the above method on a background thread like this :
[myTester performSelectorInBackground:@selector(test) withObject:nil];

and it’s not working, why is that ?

Answer 1

I figured it out. In my 2nd version the CMMotionManager instance I was creating got lost for some reason. Therefore, I changed the implementation of my MotionHandler class into this :

MotionHandler.m

@interface MotionHandler()
{
   //..
   CMMotionManager *motionManager; // I now declare it here
}

@implementation MotionHandler

@synthesize accelerationOnYaxis; // this is an int property of the MotionHandler class

-(void) startAccelerationUpdates
{
    motionManager = [[CMMotionManager alloc] init]; // and then initialize it here..
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           self.accelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
}
-(void)test
{
    [self startAccelerationUpdates];
    while(1==1)
    {
        NSLog(@"current acceleration on y-axis is: %f", self.accelerationOnYaxis);
    }
}

and now it seems to be working fine.