NSTimer target and userInfo parameter questions

4
votes

I've read around SO as well as looked at the Apple documentation for the NSTimer class, and it seems like the easiest way to create a timer is by using the following method:

[NSTimer scheduledTimerWithTimeInterval:15.0
                                 target:self
                               selector:@selector(fireThisMethod:)
                               userInfo:nil
                                repeats:NO];

I understand that this will create a timer that fires after 15 seconds. The method that will be fired will be whatever method is passed into the "selector" (in this case "fireThisMethod"). Since the "repeats" is "NO," this means that it will only be fired once. My questions are:

1) Is it possible to pass in a method to "selector" that has more than one parameter? I've seen methods without any parameters, or in this case 1 (since a ":" is present after the method name). A method such as fireThisMethod:anotherParameter:?

2) I'm not sure if I truly understand what the "target" and "userInfo" parameters are for. Will you ever have a "target" that isn't "self?" Will you have a "userInfo" that isn't nil? If so, in what scenarios?

Thanks

1
objective-cmethodsparametersselectornstimer

1 Answers

6
votes

Question 1

No. Take a look in the docs. Quoting:

The selector must have the following signature:

- (void)timerFireMethod:(NSTimer*)theTimer

Selectors for methods without arguments are wrong. The argument to be passed is the timer, so you can do things like distinguishing which timer fired from you method (in case more than one timer calls the same method).

Question 2a

The target can be any object that implements the given method. Sometimes you may want a specific object (other than self) to do the task after the timer fires.

Question 2b

This is exactly what you're looking for. userInfo can be any object, maybe a data container, a NSValue, or any other thing. Use this to pass extra information to your method which will extract it as follows:

- (void)timerFireMethod:(NSTimer*)theTimer
{
    id info = [theTimer userInfo]; /* give it an appropriate type */

    ...
}