title: iOS autolayout changes leading and trailing space
body: <p>I have some issues with auto layout, hopefully some of you can help me =).</p>
  
  <p>I add a UIView to an empty view controller, like this:
  <img src="https://i.stack.imgur.com/LvxcM.png" alt="enter image description here"></p>
  
  <p>Then I add constraints for leading and trailing space, like this:</p>
  
  <p><img src="https://i.stack.imgur.com/fEL8g.png" alt="enter image description here"></p>
  
  <p>Which results in this:</p>
  
  <p><img src="https://i.stack.imgur.com/jz1e5.png" alt="enter image description here"></p>
  
  <p>I can't understand why it sets them as equal to -16.0. If I change those values to 0, then Xcode complains about the width of the gray UIView.</p>
  
  <p>When I run the app on iPhone 5 simulator, it looks fine:
  <img src="https://i.stack.imgur.com/9lAEd.png" alt="enter image description here"></p>
  
  <p>However, when I run the app on iPhone 6 Plus simulator it adds white space on the left and on the right:</p>
  
  <p><img src="https://i.stack.imgur.com/qg6hD.png" alt="enter image description here"></p>
  
  <p>I don't want the gray UIView to have any space from the left of from the right no matter how big the screen is. How can I fix it? Thanks!</p>