Question

I have a logic issue. I need to access an instance of an object from another class.

I have a class called FacebookController. It has several delegate methods in it, for example fbDidLogin. First the facebookloginButtonClicked method gets executed when the user clicks on a button, and after some internal processing, the fbDidLogin method will get called, and the user will log in to the application. (All of this works perfectly).

Now I need to log out from the application. There is a delegate method called logout, and I have to call it as [facebook logout].

I have added a method called -(void) logoutFacebook. When the user clicks the logout button, the following method is called. The logout method is as follows;

-(void) logoutFacebook {
   [facebook logout];    
}

Logout works only if I log out (call logoutFacebook method) from the same viewController.

For instance if I am in a class called Student, I am trying to call the logoutFacebook method of FacebookController. My approach is as follows;

FacebookController *facebookController = [[FacebookController alloc]]init;

[facebookController logoutFacebook];

This doesn’t work, because by doing this, it will create a new instance of FacebookController . So I need to somehow access the original facebook object which was in the FacebookController (which was created after login). How do I get access this object ?

The code:

-(void)facebookloginButtonClicked:(id)sender{
 facebook = [[Facebook alloc] initWithAppId:@"3232232" andDelegate:self];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    if ([defaults objectForKey:@"FBAccessTokenKey"] 
        && [defaults objectForKey:@"FBExpirationDateKey"]) {

        facebook.accessToken  = [defaults objectForKey:@"FBAccessTokenKey"];
        facebook.expirationDate = [defaults objectForKey:@"FBExpirationDateKey"];
    }

    if (![facebook isSessionValid]) {        
        [facebook authorize:nil];      

    }
}
- (void)fbDidLogin {

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:[ facebook accessToken] forKey:@"FBAccessTokenKey"];
    [defaults setObject:[ facebook expirationDate] forKey:@"FBExpirationDateKey"];
    [defaults synchronize];

    }

-(void) logoutFacebook {
       [facebook logout];    
    }

Answer 1

in FacebookController.m class add this code above the @implementation

static FacebookController* Object;

add the following function to the .h file

+ (FacebookController *) sharedInstance;       

Implementation of the above function in the .m file

+ (FacebookController *) sharedInstance
{
if( Object == nil)
{
Object = [[FacebookController alloc]]init;
}

return Object;

}

Now wherever you want to use the Facebook object ..use it like this

[FacebookController sharedInstance];

Now you will only have one instance of FacebookController class in your app’s whole lifetime..This is called Singleton pattern..You can find google it to get more detail on it.

References:

• https://en.wikipedia.org/wiki/Singleton_pattern
• https://www.galloway.me.uk/tutorials/singleton-classes/