title: NSFileManager unique file names
body: <p>I need a quick and easy way to store files with unique file names on iOS.  I need to prefix the file with a string, and then append the generated unique identifier to the end.  I was hoping <code>NSFileManager</code> had some convenient method to do this, but I can't seem to find it.</p>
  
  <p>I was looking at <code>createFileAtPath:contents:attributes:</code>, but am unsure if the attributes will give me that unique file name.</p>