title: Adding Subviews on the top of MainViewController
body: <p>I am working to get user survey before user starts using my app, it is a typically collection of data for my research.</p>
  
  <p>My problem is to add subview on the top of mainviewcontroller.</p>
  
  <p>I have two subviewcontroller as you can see in the first screenshoots. I would like to add first subview on the mainviewcontroller, and whenever user clicks on next customized button, then firstsubview disappear and secondsubview appear on the top of mainviewcontroller.</p>
  
  <p>firstsubview implemented as follows:</p>
  
  <pre><code>    CGRect rect = [firstSurveyViewController.view frame];
      rect.origin.x = 5;
      rect.origin.y = 5;
      [firstSurveyViewController.view  setFrame:rect];
      [self.view addSubview:firstSurveyViewController.view];
  </code></pre>
  
  <p>But I want to drop the firstsubview and add the second when user clicks on next button.
  How could I implement?</p>
  
  <p><img src="https://i.stack.imgur.com/7GO8S.png" alt="firstSubview">
  <img src="https://i.stack.imgur.com/kWwJw.png" alt="secondSubView">
  <img src="https://i.stack.imgur.com/geIaP.png" alt="mainViewController + mainViewController"></p>