Facebook flow

new_gist_file

- (void)sessionStateChanged:(FBSession *)session 
                      state:(FBSessionState) state
                      error:(NSError *)error
{
    switch (state) {
        case FBSessionStateOpen: {
                //open!
            }
            break;
        case FBSessionStateClosed:
        case FBSessionStateClosedLoginFailed:
            // Once the user has logged in, we want them to 
            // be looking at the root view.
            break;
        default:
            break;
    }

    if (error) {
        //error
    }    
}

- (void)openSession
{
    [FBSession openActiveSessionWithReadPermissions:@[@"email"]
                                       allowLoginUI:YES
                                  completionHandler:
                                       ^(FBSession *session, 
                                         FBSessionState state, NSError *error) {
                  [self sessionStateChanged:session state:state error:error];
    }];    
}

//application:didFinishLaunchingWithOptions
if (FBSession.activeSession.state == FBSessionStateCreatedTokenLoaded) {
    // Yes, so just open the session (this won't display any UX).
    [self openSession];
} else {
    // No, display the login page.
    [self showLoginView];
}