Prevent access to UIViewControllers with tab bar c

Question

I currently encountering a problem with my iOS application.
I am attempting to incorporate a gradual login pattern, i.e.: the use can access some of the app without being required to login.

Required features are as follows:

• At all times the user can view all navigation items that require login
• When the user attempts to access an uiview(controller) that requires login, they will be prompted with a UIAlertView asking them to log in. (Preferably the UIAlertView will appear when the app recognised the initiated segue destination is restricted).

At first I used a subclass of UIViewController that, in the designated initialiser (initWithCoder), would check NSUserDefaults to see if the user was logged in. I then subclassed off of that. Limitations were as follows:

• Couldn't use other subclasses of UIViewController, namely UITableViewController
• The UIAlertView came up after the view had appeared, which i am assuming would cause errors if the subclassed UIViewController assumed the user was logged in.

Question summary:
I would like to know how to conditionally prevent users from accessing certain UIView(Controller)s and subclasses of UIViewController, and when that happens present a UIAlertView.

Update 1
Could categories and/or protocols be a viable solution?

Update 2
CodaFi pointed out singletons as a great solution to manage the user's state.

With that implemented I now need to figure out how to control the user's access.
As I am using storyboards I feel that the most versatile implementation would be subclassing UIStoryboardSegue, and on the perform method check if the user is attempting to access an restricted UIViewController (perhaps restricted controllers have a protocol property that specifies the required status: logged in/out). However the pitfall here is that you cannot choose the class/subclass of a UIStoryboardSegue in the storyboard graphic editor. I am aware that I could do it programatically, however that seems tedious as i would have to add IBActions and like that to methods that perform segues, furthermore I don't think that would work with the way elements such as navigationController and tabbarControllers behave.

Does anybody have a viable solution to restricting the user's navigation?

Update 3
I've added an answer to this question, however I still deem it as unanswered because the answer I've written doesn't take into account segues between navigation bar controllers. However it may help some people.

Answer 1

Okay, So I have part of a solution.

It only works in situations where you can choose a custom segue (and I've only written code for pushing, not modal).

Protocol "UIViewControllerAuthentication" for all controllers that require authentication, this protocol contains an method to retrieve the required authentication status.

enum authenticationStatus {
notLoggedIn = 0,
noPassword = 1,
loggedIn = 2
};

@protocol UIViewControllerAuthentication <NSObject>

-(enum authenticationStatus)authStatusRequired;

@end

Controllers that require authentication conform to this protocol:

-(enum authenticationStatus)authStatusRequired{
return loggedIn;
}

Then use this for the authenticated push segue

@interface SeguePushWithAuth : UIStoryboardSegue

@end
-(void)perform{
    NSLog(@"custom segue destination : %@",self.destinationViewController);
    NSLog(@"custom segue source : %@",self.sourceViewController);
    NSLog(@"custom segue dest conforms to protocol : %i",[self.destinationViewController conformsToProtocol:@protocol(UIViewControllerAuthentication)]);

    if([self.destinationViewController conformsToProtocol:@protocol(UIViewControllerAuthentication)]){
        UIViewController <UIViewControllerAuthentication> *destination = (UIViewController <UIViewControllerAuthentication> *)self.destinationViewController;
        if (!((int)[AccountModel userAuthStatus] >= (int)[destination authStatusRequired])) {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Authentication" message:@"You need an account to access this area" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"Login",@"Create Account", nil];
            //alert
            [alert show];
            return;
        }
    }

    [[self.sourceViewController navigationController] pushViewController:self.destinationViewController animated:true];
}

@end

Then use custom segues in uistoryboard

This is a good pattern to allow the destination controller to cancel the segue.
However its far from what I want as I want to be able to authenticate segues that link tab bar controllers to their children.

Answer 2

So, I've answered how to do this using custom segues.

Now I understand my real problem was the mental disconnect with the tabbarcontrollerdelegate protocol.

As a solution to preventing access to tabs I've made a class to handle said tab bar controller

#import <Foundation/Foundation.h>

@interface TabBarDelegate : NSObject<UITabBarControllerDelegate,UIAlertViewDelegate>{
    UITabBarController *cachedTabBarController;
}

@end

#import "TabBarDelegate.h"

@implementation TabBarDelegate

-(BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController{
    NSLog(@"%s",__FUNCTION__);
    NSLog(@"Pretending the user isnt logged in");

    if(true){
        NSString *message = [NSString stringWithFormat:@"You require an account to access %@",viewController.tabBarItem.title];
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Account Required" message:message delegate:self cancelButtonTitle:@"Okay" otherButtonTitles: @"Login",@"Create Account",nil];
        [alert show];
        //Hold tabbarcontroller property for alert callback
        cachedTabBarController = tabBarController;
        return false;
    }

    return true;
}

-(void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex{
    if(cachedTabBarController){
        switch (buttonIndex) {
            case 1:
                //Login
                [cachedTabBarController performSegueWithIdentifier:@"tabBarToLogin" sender:cachedTabBarController];
                break;
            case 2:
                //Sign up
                [cachedTabBarController performSegueWithIdentifier:@"tabBarToSignup" sender:cachedTabBarController];
                break;
            default:
                break;
        }
        //Release tab bar controller from memory
        cachedTabBarController = nil;
    }
}

@end

Then i wired it up to my appDelegate in applicationDidFinishLaunching...

//Hook up tab bar delegate
    mainTabController = (UITabBarController*)self.window.rootViewController;
    mainTabBarDelegate = [[TabBarDelegate alloc] init];
    mainTabController.delegate = mainTabBarDelegate;

And Voila