title: on iOS using Parse, how to save two PFFiles to a PFObject in background
body: <p>My app creates an object (PFUSER) for each user, and an (PF) object for each event they participate in. This works fine. then i have two files associated with that event. i save the first file to a PFFile, then associate it to the event pfobject. when i use blocks and do this in the background, how can then make sure control continues to do the same for the second file?</p>
  
  <p>I am new to blocks so maybe it would be clearer to me why its not working with callbacks, but it seems the block runs the save in another thread and the current one is abandoned before the next steps are taken.  </p>
  
  <p>Of course i'd like to do both of these as "save eventually" to allow offline use.</p>
  
  <p>any guidance / examples you can point me to greatly appreciated.</p>
  
  <p>thanks!</p>