Issue Logging in With Facebook on iOS App - ios

Question

In my app, my main screen is a TableView which shows a list of posts from a Facebook Page. I access those posts using Open Graph, which means a user has to be logged in first. So, I have it pop up with a UIAlertView which tells the user this. Clicking ok presents the FBLoginButton, which I have like this:
FBSDKLoginButton *loginButton = [[FBSDKLoginButton alloc] init];
// Optional: Place the button in the center of your view.
loginButton.center = self.view.center;
[self.view addSubview:loginButton];
Clicking the Login Button takes me to Facebook, where I give it permission. It then goes back to the app, but shows an empty TableView with a Facebook Logout button in the middle. My viewWillAppear in the app is like this:
if ([FBSDKAccessToken currentAccessToken]) {
[[[FBSDKGraphRequest alloc] initWithGraphPath:#"/v2.3/PAGEID/feed?limit=20" parameters:[NSMutableDictionary dictionaryWithObject:#"id, message, full_picture, link" forKey:#"fields"]]
startWithCompletionHandler:^(FBSDKGraphRequestConnection *connection, id result, NSError *error) {
if (!error) {
//performs code to get posts sorted into array
}
else {
NSLog(#"%#", error);
}
}];
} else {
NSLog(#"Not Logged In");
UIAlertView *login = [[UIAlertView alloc] initWithTitle:#"Please Login" message:#"Stronger Marriages now requires a login to Facebook in order to access its latest posts and messages. Thank you!" delegate:self cancelButtonTitle:nil otherButtonTitles:#"Ok", nil];
[login show];
}
I had thought that once I have given it permission, it would go back to the app, run the viewWillAppear code, and see there was a currentAccessToken and perform the code, but this is not happening. If I now force close the app, it will show everything fine, with no logout button visible. How do I get it to do this once it redirects to app after logging in?

Answer 1

The easiest way to respond directly to a login via the FBSDKLoginButton is by making your ViewController implement the FBSDKLoginButtonDelegate protocol.
You can call the loginButton:didCompleteWithResult:error: function in this protocol to immediately respond to a login as soon as the user returns to your app from Facebook. It would look something like this:
- (void) loginButton:(FBSDKLoginButton *)loginButton
didCompleteWithResult:(FBSDKLoginManagerLoginResult *)result
error:(NSError *)error {
if ([result token]) {
// Your code here
} else {
NSLog(#"Not Logged In");
// Show error here
}

Answer 2

I'm not sure why viewWillAppear doesn't get called, but I have a different solution. When the Facebook token changes, the SDK sends out a notification. You can subscribe to this, perhaps in your viewDidLoad, and run your code in the callback.
[[NSNotificationCenter defaultCenter] addObserverForName:FBSDKAccessTokenDidChangeNotification
object:nil
queue:[NSOperationQueue currentQueue]
usingBlock:^(NSNotification *note) {
NSLog(#"received access token change notif");
// do your stuff here
}];