title: Yii cannot Instantiate controller
body: <p>As I see if we want to instantiate a Model (for example named <code>Post</code>), we just have to call:</p>
  
  <pre><code>$post = new Post();
  </code></pre>
  
  <p>Now, I also want to instantiate a <code>Controller</code> (for example named <code>Post</code>, and php file for this controller named <code>PostController.php</code>). So I use this code:</p>
  
  <pre><code>$postController = new PostController();
  </code></pre>
  
  <p>However, I get an error when running this code.</p>
  
  <p>I did some searching and found that it should be like the following to instantiate:</p>
  
  <pre><code>$postController = Yii::app()-&gt;createController('post/index');
  </code></pre>
  
  <p>It runs correctly. But I still wonder why the first approach doesn't work?</p>