首次尝试Facebook iOS SDK登录失败，但第二次成功

Question

Ok, so this has been a tough one for me to debug because I do not experience this problem that many users of my app appear to be experiencing. If you would like to try it yourself, you may download the app on iTunes by searching for "syncquik".

PROBLEM: When users attempt to login to my app via the Facebook login button, the first attempt to open an active FB session often fails. At first, I thought this was because they had to turn on the app's Facebook privacy settings in the iPhone's general settings. However, because so many are having the same issue, I am beginning to wonder if it's because of an error in my code (see below)? I followed the demo example and Facebook instructions, but perhaps I missed something? Thanks in advance for any help you can offer!

CODE:

(In ViewController holding FB button):

- (IBAction)fbSignIn:(id)sender
{
    AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;
    [appDelegate openSession];
}

(In AppDelegate.m):

- (void)sessionStateChanged:(FBSession *)session
                  state:(FBSessionState) state
                  error:(NSError *)error
{
NSLog(@"FB Session State Changed");
switch (state) {
    case FBSessionStateOpen: {
            NSLog(@"FBSessionStateOpen");
            if (fbButtonPushed && FBSession.activeSession.isOpen) {
                [self sendUserFbInfo];
                fbButtonPushed = NO;
            }
    }
        break;
    case FBSessionStateClosed:
        NSLog(@"FBSessionStateClosed");
        break;
    case FBSessionStateClosedLoginFailed:
        NSLog(@"FBSessionStateClosedLoginFailed");
        [FBSession.activeSession closeAndClearTokenInformation];
        [self showLoginView];
        break;
    default:
        break;
}

if (error) {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Please Try Again" message:@"If second attempt is unsuccessful, then set SyncQuik to ON in Settings > Facebook." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alertView show];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"com.syncquik.connectionrequest.complete" object:nil];
}    

}

- (void)openSession
{
    NSLog(@"Opening a User's FB Session");
    fbButtonPushed = YES;
    NSArray *permissons = [[NSArray alloc] initWithObjects:@"email", nil];
    [FBSession openActiveSessionWithReadPermissions:permissons
                                       allowLoginUI:YES
                                  completionHandler:
                                        ^(FBSession *session,
                                          FBSessionState state, NSError *error) {
                [self sessionStateChanged:session state:state error:error];
     }];
}

- (BOOL)application:(UIApplication *)application
    openURL:(NSURL *)url
  sourceApplication:(NSString *)sourceApplication
         annotation:(id)annotation
{
    return [FBSession.activeSession handleOpenURL:url];
}

- (void)showLoginView
{
    NSLog(@"Show Login View");
    //Anything else need to be placed here?
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [FBSession.activeSession handleDidBecomeActive];
    if (fbButtonPushed && FBSession.activeSession.isOpen) {
        [self sendUserFbInfo];
        fbButtonPushed = NO;
    }
}

Answer 1

if (self.session.state != FBSessionStateCreated) {
        // Create a new, logged out session.
        [self openSession];
    }
 else{
    [FBSession setActiveSession:self.session];
    [self sessionStateChanged:session state:state error:error];
 }

try this code in openActiveSessionWithReadPermissions block