title: GPUImageStillCamera is not working
body: <p>I have a <code>UIViewController</code> which has a child hierarchy like this<br/>
  <img src="https://i.stack.imgur.com/veugg.png" alt="enter image description here"></p>
  
  <p>and then, I use this code to show camera preview<br/></p>
  
  <pre><code>stillCamera = [[GPUImageStillCamera alloc] init];
  stillCamera.outputImageOrientation = UIInterfaceOrientationPortrait;
  
  filter = [[GPUImageStretchDistortionFilter alloc] init];
  [filter prepareForImageCapture];
  [stillCamera addTarget:filter];
  GPUImageView *filterview = [[GPUImageView alloc] init];
  _preview = filterview;
  [filter addTarget:filterview];
  
  [stillCamera startCameraCapture];
  </code></pre>
  
  <p>variable <code>_preview</code> is a <code>UIView</code> whose class is set to <strong>"GPUImageView"</strong>. On the hierarchy image above, it is the selected one.</p>
  
  <p>When I showed the view, it showed nothing on <code>_preview</code>. Just a blank <code>UIView</code>. What did I do wrong?</p>
  
  <p>When I changed the line <code>_preview = filterview</code> to <code>self.view = filterview</code>, it worked as expected. Does it have to be <code>self.view</code>?</p>