How to make my CMMotionManager available through a singleton? - ios

Question

So I have been designing an iOS game (in Sprite Kit) for a while now and just recently added a CMMotionManager to my project so that my character would be controlled by the tilt of the screen. It took some fiddling but I got it to work, and here's how I've implemented it:
In my initWithSize method I have
self.motionManager = [[CMMotionManager alloc] init];
self.referenceAttitude = nil;
Then, I've written methods beginMotionSensing and switchToLiveSensing. The first is intended to get an idea of how the phone is being held and the second starts the game itself. Using SKActions, I call the first method, wait a second, and call the second. They look something like this:
-(void)beginMotionSensing{
CMDeviceMotion *deviceMotion = self.motionManager.deviceMotion;
CMAttitude *attitude = deviceMotion.attitude;
self.referenceAttitude = attitude;
[self.motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue currentQueue] withHandler:^(CMDeviceMotion *motion, NSError *error) {
[self setNull:motion];
}];
self.motionManager.deviceMotionUpdateInterval = .3;
}
and,
-(void)switchToLiveSensing{
gameIsLive = YES;
[self.motionManager stopDeviceMotionUpdates];
[self.motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue currentQueue] withHandler:^(CMDeviceMotion *motion, NSError *error) {
[self captureRoll:motion];
}];
self.motionManager.deviceMotionUpdateInterval = .02;
}
So I had all of this set up and it was working great, until I added the ability to play the game more than once. Before this, I would simply have to close out of the app and quit the game when I lost. Obviously this became annoying so I added a "game over" scene, with the ability to go back and play the game scene again. The game scene is presented again like this:
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
SKTransition *transition = [SKTransition fadeWithColor:[UIColor colorWithRed:147.0/255.0 green:213.0/255.0 blue:216.0/255.0 alpha:1.0] duration:2.0f];
MyScene *gameScene = [MyScene alloc];
gameScene = [gameScene initWithSize:self.frame.size passedInFuel:100];
[self.view presentScene:gameScene transition:transition];
}
I had remembered someone saying something in a previous post about a singleton - the comment was directed at someone implementing a CMMotionManager. They had said something along the lines of, "you should probably make it accessible through a singleton if you are going to initialize your class more than once." Well, sure enough, that's what I'm doing now. I had forgotten about this until I was playing the game and noticed that suddenly the phone seemed to ignore my tilt and went along with it's own business, killing my character in the process. It hasn't happened since, but is clearly something that needs to be fixed.
Could someone help me implement this so-called "singleton"?

Answer 1

I'm not convinced this is the problem you had, as the CMMotionManager object should be released anyway when your SKScene goes away. Can you duplicate the problem by starting the game again quickly after it ends?
You could probably do it by adding a class method in your main view/navigation controller (which ever one stays around longest) to create a singleton and then make it available to your SKScene object.
e.g.
+ (CMMotionManager *)sharedInstance
{
static CMMotionManager *sharedCMMM = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedCMMM = [[CMMotionManager alloc] init];
// Do any other initialisation stuff here
});
return sharedCMMM;
}