Calling View from Class - iphone

Question

I think I have a simple issue with my app.
First of all I am using the PraseSDK in order to use the LoginView they offer.
Now I was going to create that function and let it called by a view controller in
-(void) viewDidLoad
It worked perfectly.
Now I was wondering if I can put that code into a global function class?
Well I created a Class called: glo_function
Inside of it I created a function which is call
+(void) CallLoginScreen{
PFLogInViewController *login = [[PFLogInViewController alloc] init];
login.fields = PFLogInFieldsUsernameAndPassword | PFLogInFieldsLogInButton;
[self presentModalViewController:login animated:NO];}
In My ViewController Iam using "callLoginScreen" like this
[glo_function CallLoginScreen]
The methode is going to be called by the View Controller but the view will not show up.
Well I get that error will trying to run the app.
No known class method for selector 'presentModalViewController:animated:'
So I am pretty sure It do to the fact that I used the "self" in->
[self presentModalViewController:login animated:NO]
Can someone help me out with it? should be easy, hopefully :)
-----------------------Response------------------------------
Hi after I did that, the app crashes.
The Call methode looks like that:
[glo_function showLoginScreenUsingViewController];
In glo_function.m the methode looks like that:
+ (void)showLoginScreenUsingViewController:(UIViewController *)VC {
PFLogInViewController *login = [[PFLogInViewController alloc] init];
login.fields = PFLogInFieldsUsernameAndPassword | PFLogInFieldsLogInButton;
[VC presentModalViewController:login animated:NO];}
The Result when starting the App:
2012-12-28 21:20:24.003 Logbuch40[1942:c07]
*** Terminating app due to uncaught exception 'NSInvalidArgumentException'
, reason: '+[glo_function showLoginScreenUsingViewController]:
unrecognized selector sent to class 0x22e9ec

Answer 1

"self" always refers to the object you are in. In your case it's the glo_function object. So when you say self you are talking to the wrong object.
You could still do what you want but in your glo_function method you need to pass in a reference to your view controller. Then just use that in your function instead of self.
+ (void)showLoginScreenUsingViewController:(UIViewController *)VC {
PFLogInViewController *login = [[PFLogInViewController alloc] init];
login.fields = PFLogInFieldsUsernameAndPassword | PFLogInFieldsLogInButton;
[VC presentModalViewController:login animated:NO];
}