title: iOS URLForUbiquityContainerIdentifier: Always returns nil
body: <pre><code>[[NSFileManager defaultManager] URLForUbiquityContainerIdentifier:nil]
  </code></pre>
  
  <p>Before iOS9, when icloud up to is active program installed for the first time, this method returns the url. But in the iOS9 installation for the first time, it returns nil, only the second startup program, did not return to the url,why?</p>