Question

Im making a class that creates a timer that then calls a void using @selector or (SEL). The app crashes when [mytimer timer…]; is called because “unknown selector called”. The error is that it isnt finding the void I’m giving to it but i know that the void works fine. My question is how to I write the myselector part correctly?

+ (void) timer:(NSTimer*)timer interval:(int)interval selector:(SEL)myselector   
{
timer = [NSTimer scheduledTimerWithTimeInterval:interval
                                         target:self
                                       selector:myselector
                                       userInfo:nil
                                        repeats:YES];
}

This is the method being implemented:

[mytimer timer:NameOfTimerTheWorks interval:0.1 selector:@selector(myVoid)];

... 

- (void)myVoid
{
Do stuff
}

Also I understand that this class looks completely useless but there is more to it that I didnt include. My problem revolves around the selector.

Answer 1

There’s nothing wrong with your use of @selector(), your issue is with Objective C classes, and what self means in different scopes.

The problem is that you’re creating your timer in a class + method and self at that point is not the instance you want, it’s actually the Class itself. I wouldn’t be doing it in a class method, but if you must, just pass in the reference to the target and it should send th message your’e expecting.

Change your implementation to the following so you pass in the target, and return the timer

+ (NSTimer *)timerWithTarget:(id)target 
     interval:(int)interval 
     selector:(SEL)myselector   
{
  return [NSTimer scheduledTimerWithTimeInterval:interval
                                           target:target
                                         selector:myselector
                                         userInfo:nil
                                          repeats:YES];
}


NameOfTimerTheWorks = [mytimer timetWithTarget:self interval:0.1 selector:@selector(myVoid)];

- (void)myVoid
{
  //Do stuff
}

Additionally, in Objective C the standard way to name classes is with a capital letter, and camel case where appropriate. Your class should be MyTimer and not mytimer and iVars are lowercase eg nameOfTimerTheWorks.