Question

I’m currently trying the Facebook’s single sign on function in my mobile app. So far, I could reach the Facebook Auth Dialog as I test my app. But when I click the OK button as I authorize the app, my view gives me a black screen. I wonder if this is because of the assignment of the rootViewController.

In this line of code in my FbSSOTrialDelegate.m

self.window.rootViewController = self.FbSSOTrialVC;

I get a warning saying Incompatible pointer types assigning to 'UIViewController *' from 'FbSSOTrialViewController *' and also this log in my console:

2012-07-09 11:17:04.798 FbSSOTrial[976:f803] Application windows are expected to have a root view controller at the end of application launch

I say it’s quite weird because I’m sure that FbSSOTrialVC is a subclass of UIViewController

Kindly enlighten me on why is this happening. Below were the other codes for the FbSSOTrialViewController.h

#import <UIKit/UIKit.h>

@interface FbSSOTrialViewController : UIViewController

@end

and appDelegate

FbSSOTrialDelegate.h

#import <UIKit/UIKit.h>
#import "FBConnect.h"

@class FbSSOTrialViewController;


@interface FbSSOTrialAppDelegate : NSObject <UIApplicationDelegate, FBSessionDelegate>
{
    Facebook *facebook;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet FbSSOTrialViewController *FbSSOTrialVC;
@property (nonatomic, retain) Facebook *facebook;

@end

FbSSOTrialDelegate.m

#import "FbSSOTrialAppDelegate.h"

@implementation FbSSOTrialAppDelegate

@synthesize window = _window;
@synthesize facebook = _facebook;
@synthesize FbSSOTrialVC = _FbSSOTrialVC;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    NSString *FbAppId = @"MY_APP_ID";

    self.window.rootViewController = self.FbSSOTrialVC;
    [self.window makeKeyAndVisible];

    self.facebook = [[Facebook alloc] initWithAppId:FbAppId andDelegate:self];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    if ([defaults objectForKey:@"FBAccessTokenKey"] && [defaults objectForKey:@"FBExpirationDateKey"]) {
        self.facebook.accessToken = [defaults objectForKey:@"FBAccessTokenKey"];
        self.facebook.expirationDate = [defaults objectForKey:@"FBExpirationDateKey"];
    }

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

    return YES;
}

Answer 1

From our discussion, it was decided that the view controller was not being properly instantiated during the application launch. We determined that the ViewController of interest is coming from a storyboard, so the recommended code change is as follows:

// remove this
// self.window.rootViewController = self.FbSSOTrialVC;

// and replace it with:
self.FbSSOTrialVC = [self.window.rootViewController.storyboard instantiateViewControllerWithIdentifier:@"Fb SSO Trial VC"];
self.window.rootViewController = self.FbSSOTrialVC;

Note that this requires that in the storyboard, the ViewController of interest should have the identifier “Fb SSO Trial VC” (change these as appropriate).