title: How does ios manage ViewController's memory
body: <p>If i got three ViewControllers called VC1, VC2, VC3. And in every <code>ViewController</code>, there is lots of <code>ImageViews</code>.</p>
  
  <p>If i navigate these ViewControllers like this with <code>pushViewController</code> method:</p>
  
  <pre><code>VC1 -&gt; VC2 -&gt; VC3
  </code></pre>
  
  <p>So does the memory of image allocated in VC1 will be released? 
  If not, did we need to release and load image in VC1 when navigating to save memory?</p>