title: Auto Layout with UITabBarController
body: <p>I'm trying to shift to Auto Layout in my app, but I'm having some trouble with my <code>UITabBarController</code>. Basically, I have two buttons on my home screen, and I want them to have equal sizes, one 50 pixels from the top of the screen and one 50 pixels from the bottom.</p>
  
  <p>The issue is that when I do this:</p>
  
  <pre><code>NSArray* verticalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-50-
      [buttonOne(150)]" options:0 metrics:nil 
      views:NSDictionaryOfVariableBindings(buttonOne)];
  [self.view addConstraints:verticalConstraints];
  
  verticalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:
      [buttonTwo(==buttonOne)]-50-|" options:0 metrics:nil 
      views:NSDictionaryOfVariableBindings(buttonOne, buttonTwo)];
  [self.view addConstraints:verticalConstraints];
  </code></pre>
  
  <p>The bottom button is 50 pixels from the bottom of the view, which is 568 points tall, when the height of <code>self.view</code> should be the screen height minus the tab bar's height (the navigation bar is hidden). The majority of this padding is eaten up by the height of the tab bar.</p>
  
  <p><strong>My questions is: Why is my view controller's view not resizing so that it doesn't count the space <em>under</em> my tab bar as part of its height?</strong></p>