Arguments in @selector

You could use the NSTimer method:

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds
                                 invocation:(NSInvocation *)invocation
                                    repeats:(BOOL)repeats;

Instead, since an NSInvocation object will allow you to pass arguments; an NSInvocation object is, as the docs define it:

an Objective-C message rendered static, that is, it is an action turned into an object.

Whilst creating an NSTimer object using a selector requires the format of the method being:

- (void)timerFireMethod:(NSTimer*)theTimer

An NSInvocation allows you to set the target, the selector, and the arguments that you pass in:

SEL selector = @selector(myMethod:setValue2:);

NSMethodSignature *signature = [MyObject instanceMethodSignatureForSelector:selector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
[invocation setSelector:selector];

NSString *str1 = @"someString";
NSString *str2 = @"someOtherString";

//The invocation object must retain its arguments
[str1 retain];
[str2 retain];

//Set the arguments
[invocation setTarget:targetInstance];
[invocation setArgument:&str1 atIndex:2];
[invocation setArgument:&str2 atIndex:3];

[NSTimer scheduledTimerWithTimeInterval:0.1 invocation:invocation repeats:YES];

Where MyObject is the class that myMethod:setValue2: is declared and implemented on – instanceMethodSignatureForSelector: is a convenience function declared on NSObject which returns an NSMethodSignature object for you, to be passed to NSInvocation.

Also, to note, with setArgument:atIndex:, the indices for arguments to be passed to the method set as the selector start at index 2. From the docs:

Indices 0 and 1 indicate the hidden arguments self and _cmd, respectively; you should set these values directly with the setTarget: and setSelector: methods. Use indices 2 and greater for the arguments normally passed in a message.

For scheduledTimerWithTimeInterval:, the selector you pass can only have one argument. Further, its one argument must be an NSTimer * object. In other words, the selector must take the following form:

- (void)timerFireMethod:(NSTimer*)theTimer

What you could do is store the arguments in the userInfo dictionary and call the selector you want from the timer callback:

- (void)startMyTimer {
    /* ... Some stuff ... */
    [NSTimer scheduledTimerWithTimeInterval:0.1 
                                     target:self 
                                   selector:@selector(callMyMethod:) 
                                   userInfo:[NSDictionary dictionaryWithObjectsAndKeys:someValue, 
                       @"value1", someOtherValue, @"value2", nil] 
                                    repeats:YES];
}

- (void)callMyMethod:(NSTimer *)theTimer {
    NSString *value1 = [[theTimer userInfo] objectForKey:@"value1"];
    NSString *value2 = [[theTimer userInfo] objectForKey:@"value2"];
    [self myMethod:value1 setValue2:value2];
}

Looks like a job for blocks (assuming this is targeted for Snow Leopard.)

-jcr