Facebook SDK: AccessToken.CurrentAccessToken always null, even after logging in - ios

Question

I am using the following code (on Xamarin) to log in using the latest Facebook SDK (I am also using Parse to manage my backend):
partial void LoginWithFacebook (UIButton sender)
{
LoginManager login = new LoginManager();
login.LogInWithReadPermissionsAsync(kPermissions).ContinueWith(t => {
if (t.IsFaulted && t.Exception != null) {
Console.Error.WriteLine("Error while authenticating: {0}", t.Exception.Message);
} else {
var result = t.Result;
if (result.IsCancelled) {
Console.Error.WriteLine("User canceled the operation");
} else {
Console.WriteLine("Authenticated!");
ParseFacebookUtils.LogInAsync(result.Token.UserID, result.Token.TokenString, (DateTime)result.Token.ExpirationDate).ContinueWith(loginTask => {
if (!loginTask.IsFaulted) {
InvokeOnMainThread(() => PerformSegue("GoToDashboard", null));
} else {
Console.Error.WriteLine("Could not login to Parse");
}
});
}
}
});
}
And then, to load the friends list (who are also using the App) I use the following code:
if (AccessToken.CurrentAccessToken != null) {
var request = new GraphRequest ("me/friends", null);
request.Start (new GraphRequestHandler ((connection, result, error) => {
if (error != null) {
Console.Error.WriteLine("Error fetching the friends list");
} else {
Console.WriteLine("Result: {0}", result);
}
hud.Hide(true);
}));
}
But the AccessToken always seem to be null even if the authentication is successful. I tried setting it by hand after the authentication but when the App restarts, it is lost again.
EDIT
I have removed the condition "if (AccessToken.CurrentAccessToken != null)" and it makes the request with no problems so I guess I am just using the wrong way to detect if the user is logged in. What's the correct way?

Answer 1

Thanks to the question referenced by #VijayMasiwal I was able to discover the problem. I had forgot to initialize Facebook in the App Delegate.
Here is how the FinishedLaunching method should be implemented when using Facebook:
public override bool FinishedLaunching (UIApplication application, NSDictionary launchOptions)
{
Settings.AppID = kFacebookAppID;
Settings.DisplayName = kFacebookDisplayName;
// I had forgotten this line :)
return ApplicationDelegate.SharedInstance.FinishedLaunching (application, launchOptions);
}
Hope that helps.