title: Facebook SDK v4.0 for iOS - FBSDKProfile currentProfile not being set
body: <p>I've just "upgraded" my Facebook SDK to 4.0 for my iOS app. </p>
  
  <p>I've got the log in working okay, however, according to the documentation, I'm now supposed to use <code>FBSDKProfile.currentProfile()</code> to access profile information. </p>
  
  <p>However, this value always seems to be <code>nil</code>, even though my profile picture is being displayed (through a <code>FBSDKProfilePictureView</code>) and my <code>FBSDKAccessToken.currentAccessToken()</code> is not <code>nil</code>. </p>
  
  <p>This is my login <code>ViewController:</code></p>
  
  <pre><code>import UIKit
  
  class LoginViewController: UIViewController, FBSDKLoginButtonDelegate {
  
      @IBOutlet weak var fbLoginButton: FBSDKLoginButton!
      @IBOutlet weak var fbProfilePicture: FBSDKProfilePictureView! //displays a picture
  
      override func viewDidLoad() {
          super.viewDidLoad()
          self.fbLoginButton.delegate = self
          FBSDKProfile.enableUpdatesOnAccessTokenChange(true)
          if FBSDKAccessToken.currentAccessToken() != nil {
              println("\(FBSDKAccessToken.currentAccessToken().userID)") //works
          }
          self.fbLoginButton.readPermissions = ["public_profile", "email", "user_friends"]
      }
  
      override func didReceiveMemoryWarning() {
          super.didReceiveMemoryWarning()
      }
  
      func loginButton(loginButton: FBSDKLoginButton!, didCompleteWithResult result: FBSDKLoginManagerLoginResult!, error: NSError!) {
          println(FBSDKProfile.currentProfile()) //is nil
      }
  
      func loginButtonDidLogOut(loginButton: FBSDKLoginButton!) {
      }
  }
  </code></pre>
  
  <p>Any ideas?</p>