Storing accessToken in Facebook iOS SDK

I have the Facebook iOS SDK set up in my app. However, I 开发者_运维知识库have trouble determining when my session is finished. How to check if it's finished, and where (how) to store the access token received by the login?

I need to determine whether I have the access token or not right from the beginning so I know whether to log in again, or go forward in the app.

Are you familiar with NSUserDefaults ? It is for storing preferences for your app.

They are extremely easy to use, and probably what you are looking for. So it's just something like ..

NSUserDefaults *factoids;
NSString *whateverIDstring; // make this a property for convenience  

factoids = [NSUserDefaults standardUserDefaults];
self.whateverIDstring = [factoids stringForKey:@"storeTheStringHere"];

if ( ( whateverIDstring == Nil ) || ( [whateverIDstring isEqualToString:@""] ) )
    // it does not yet exist, so try to make a new one...
else
    // we already made one last time the program ran

// when you make a new one, save it in the prefs file like this...   
[factoids setObject:yourNewString forKey:@"storeTheStringHere"];
[factoids synchronize];

Hope it helps!

ONE get the preferences in to 'factoids' as in the example above

TWO decide on a name for your preference. 'storeTheStringHere' in the example.

THREE get your string 'whateverIDstring' in the example using stringForKey:

FOUR check if it is either nil or blank. if so, start fresh.

FIVE once you get the value, save it as shown!

Hope it helps!