objective-c: Calling a void function from another controller

i have a void, like -(void) doSomething in a specific controller. i can call it in this controller via [self doSomething], but i don't know how to call this void from another .m file.

I want to call it in a -(IBAction) action:(id)sender

I've tried using performSelector, but i got a 'unreconie开发者_如何学编程zd selector send' in the log. I've no idea if i have to use the notification center, or delegate...

Thanks, ronan.

You have to have an instance of the first controller (the one where you declare the function in) in your second controller.

FirstViewController *firstController = [[FirstViewController alloc] init];
[firstController doSomething];

If your first controller is declared somewhere else, and you want your second controller to know about it, have a property of FirstViewController type in your second controller, and initialize it when you need it with your FirstViewController instance.
Sometimes, this can be quite complicated to do if you have multiple controller instances and you want every one of them to know about all the others, so I would rather suggest rewriting your method to a class method:

+ (void) doSomething;

so you could call it from anywhere with

[FirstViewController doSomething];

if you have the object you want to call it on and the method is public, then you just:

[object doSomething];

The problem is that you have two controllers who don't know about each other's existence. The notification center certainly is the way to deal with this situation: the advantage is that you need not establish a formal connection between the two.

The delegate method is another possibility, but then you have to either establish the connection via an IBOutlet in Interface Builder, or you must have one controller create the other controller and pass itself as the delegate. This ties them together more closely, which may or may not be appropriate. If the only connection between the two controllers is the calling of one -(void) method, then I'd go with NSNotification.