title: change the uiview frame when it has some constraints
body: <p>There is a subview (UIView) on the main view, I want change the size of the subview (_test).</p>
  
  <p><code>_test</code> has two constraints:</p>
  
  <ol>
  <li>top space to main view: 20</li>
  <li>trailling space to main view: 136</li>
  </ol>
  
  <p>When I want change the size of _test (subview),but this seems not work:</p>
  
  <pre><code>self._test.frame = CGRectMake(self._test.frame.origin.x + 10, 
                                self._test.frame.origin.y, 
                                self._test.frame.size.width - 10, 
                                self._test.frame.size.height);
  </code></pre>
  
  <p>I think this is because constraints, but, how can I do that?</p>