title: Wait for Parse query to complete before updating UI
body: <p>First of all, I'm using Storyboards, the Parse backend and objective-c (IOS8 project)</p>
  
  <p>I've a got a ViewController that downloads a specific column from the row that is currently open. I also got a container within this ViewController that sends a new query, but that query needs the column value from VC1. As this doesn't download before the container launches, an exception is thrown as it tries to compare with (null).</p>
  
  <p><strong>Like so: (valueFromMainVC is null until VC1 completes its download)</strong></p>
  
  <pre><code>[query whereKey:@"MyColumn" equalTo:valueFromMainVC];
  </code></pre>
  
  <p>this happens in the -(PFQuery *)queryForTable method</p>
  
  <pre><code>-(PFQuery *)queryForTable {
  }
  </code></pre>
  
  <p>How can I solve this? I tried to use a while(){} statement so that it wouldn't begin until valueFromMainVC is downloaded, but I didn't have any success with that.</p>
  
  <p>(I'm using Singleton to share valueFromMainVC between ViewControllers. As well as other values)</p>
  
  <p>Help is much appreciated!</p>
  
  <p>Thanks!
  Erik</p>