iOS Not responding to Shake motion

[PizzaTray]

Hi everyone,

I'm using the same code to every app i've made to make some action after "Shake" motion. From some reason that i can't find out, in my new app its not working.

- (BOOL)canBecomeFirstResponder {
	return YES;
}

- (void)viewDidAppear:(BOOL)animated {
   // [super viewDidAppear:animated];
    [self becomeFirstResponder];
}

- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event {
	if (event.type == UIEventSubtypeMotionShake) {
               //Do somthing..
	}
}

What are the situations that shake motion not responding?