Question

i’m studying ios programming. but i have a problem that is UIAccelerometer.

here’s code first.

- (void)viewDidLoad {
UIAccelerometer *accelerometer = [UIAccelerometer sharedAccelerometer];
accelerometer.delegate = self;
accelerometer.updateInterval =  kUpdateInterval;
[super viewDidLoad];
}

- (void)accelerometer:(UIAccelerometer *)accelerometer 
    didAccelerate:(UIAcceleration *)acceleration {

[(BallView *)self.view setAcceleration:acceleration];
[(BallView *)self.view draw];
}

first question is viewDidLoad, i use a method that is sharedAccelerometer

and it returns a shared object for a system.

when viewDidLoad is ended, does not local variable,accelerometer, disappear??

i think that when i get a accelerometer object, and it’s gone.

because viewDidLoad is ended, and i don’t have a instance variable about that.

that’s just local variable.

second is delegate method.

i say, accelerometer.deleate = self in viewDidLoad.

but i don’t have a instance variable about accelerometer, so

how that method is called, when viewDidLoad is ended?

i really don’t understand about how can i keep UIAccelerometer object.

please help me.

Answer 1

[UIAccelerometer sharedAccelerometer] will always return the same accelerometer object (a singleton), so you can use it anywhere.