title: Hold NSOperationQueue until previous operation completes
body: <p>I want to perform few operations and need to start the next operation only upon completion of the previous one. The operation I'm adding will send async call to the server and receive data. I want to start the next operation only after the first call to the server finish receiving data from the server. How to do that?</p>
  
  <pre><code>{.... 
       PhotoDownloader *pd = [[PhotoDownloader alloc] init];
       [GetGlobalOperationQueue addOperation:pd]; 
  }
  </code></pre>
  
  <p>Inside the PhotoDownloader I will allocate the required parameters and call a Global function which handles all the request</p>
  
  <pre><code>[GlobalCommunicationUtil sendServerReq:reqObj withResponseHandler:self];
  </code></pre>
  
  <p>Inside the sendServerReq method I will construct the URL request and send it to the server and this call is a "sendAsynchronousRequest" call. The PhotoDownloader will have the CommunicationUtil's delegate methods.</p>