Can't able to access email field using facebook sdk for IOS

Question

I'm using the Graph API, but I can't figure out how to get a logged-in users email address.

[FBSession openActiveSessionWithReadPermissions:@[@"public_profile", @"email"] allowLoginUI:NO
            completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {
    // Handler for session state changes
    // This method will be called EACH time the session state changes,
    // also for intermediate states and NOT just when the session open
    [self sessionStateChanged:session state:state error:error];
}];