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Hi,

I am trying to create an NSTimer whose selector is a method which has multiple parameters (one of which being the actual timer). How is this done? Here is the code I’ve got so far:

…

I’m getting a “parse error before numeric constant” message when I try to compile.

Thanks for the help.

The message which NSTimer sends must have the following signature: - (void) doSomething: (NSTimer *) aTimer, that is, it takes one and only one argument. To pass additional parameters, you use the userInfo argument when you create the timer. It can be any object or even a collection of objects (NSDictionary, NSArray, NSIndexSet, etc), and in your case I guess it should be NSNumber. In your -playMovie: implementation you use [timer userInfo] to get the necessary parameter(s). And, by the way, -playMovie: should not return anything - it’s void.

OK I see, I got that to work. But I have another problem. What I am trying to do is have different timers with different intervals all call the same method, with a different parameter each time. It works fine with a single timer, but when I add extra ones, I get an error. Here is the code:

…

And this is what I get when looking in the debugger window (I think it’s a stack trace):

#0 0xfffeff10 in objc_msgSend_rtp #1 0x9295f994 in -[NSCFTimer initWithFireDate:interval:target:selector:userInfo:repeats:] #2 0x9295f800 in +[NSTimer scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:] #3 0x000317f8 in -[MyController initTimers] at MyController.m:36 #4 0x000316bc in -[MyController init] at MyController.m:17

Thanks again.

What are STRETCH and BLINK? What is the error you get in the debugger console when this happens?

That is a stack trace, yes. I’d recommend you read CocoaIntroduction and get to know how Objective-C and C in general work.

I figured out what it is. It had nothing to do with the timer, STRETCH and BLINK are #defined ints in the header file and I was getting a warning about not casting them to pointers before passing them to the function.

The problem is that ints aren’t objects. NSTimer is trying to retain them, but it explodes because you’re saying “pretend 3 is a full-blown NSObject subclass” in your code. Use NSNumber to pass the values through.

Today’s lesson is: never ignore warnings. They are there for a reason, and they usually mean that something is wrong with your code. When you get to the point of posting a question, make sure you include any warnings you don’t understand. You may not be able to resolve them but you definitely shouldn’t ignore them.

What the previous respondent said: Never ignore warnings! The warnings aren’t saying Cast those integers to a pointer before passing them in. They’re saying This parameter must be an NSDictionary. In particular, a userInfo will always be an NSDictionary, so you’ll need to create an NSDictionary containing the additional data you want to associated with your NSTimer, and pass that as the userInfo when creating it.

A minor correction: an NSTimer’s userInfo can be any object, not just an NSDictionary.

Do you mean that my NSTimer should be initialized in the following way?

… enum { BLINK=1, STRETCH, OTHER } … stretchTimer = [NSTimer scheduledTimerWithTimeInterval:[stretchInterval doubleValue] target:self selector:@selector(playMovie:) userInfo:[[NSNumber alloc] initWithInt:STRETCH] repeats:YES]; …

Is that efficient? It seems like there’s some useless overhead by adding that NSNumber.

It doesn’t matter if it’s efficient or not: you don’t have a choice in the matter. You have to pass an object (or nil for no object) there, not an unwrapped number. See PrematureOptimization for reasons why you shouldn’t worry about the overhead.

Also, userInfo should be autoreleased to avoid a memory leak: use [NSNumber numberWithInt:STRETCH] instead of [[NSNumber alloc] initWithInt:STRETCH]. The timer will retain it as necessary.

OK I see. The last thing I would like to do with this timer is to re-set its interval. I don’t see a setTimeInterval method in the class, so does that mean I have to create a new NSTimer each time I want to change the timeInterval? Also, when I create the new NSTimer over the old one, do I have to call [myTimer release] first?

stretchTimer = [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:@selector(playMovie:) userInfo:[NSNumber numberWithInt:STRETCH] repeats:YES]; // later… [stretchTimer release]; stretchTimer = [NSTimer scheduledTimerWithTimeInterval:25.0 target:self selector:@selector(playMovie:) userInfo:[NSNumber numberWithInt:STRETCH] repeats:YES];

-Thanks.

Yes, you’ll need to make a new timer. As to whether to release the old one, see MemoryManagement. Timers are like any other object and they follow the same rules of memory management as the rest. You’ll want to do [timer invalidate] to stop it from firing, though.

Do I want it to stop firing? If I don’t call [timer invalidate], won’t it just keep firing using the new NSTimer with the new interval? Or will it fire both timers because the reference to the old NSTimer is maintained in the run loop?