title: weird gap when using uiscrollview and uilabel
body: <p>here is the problem i have a tow muti-line label with many content, so I use a scroll view to show them all</p>
  
  <p>then I follow this to do the autolayout: <a href="https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/AutoLayoutbyExample/AutoLayoutbyExample.html#//apple_ref/doc/uid/TP40010853-CH5-SW2" rel="nofollow noreferrer">https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/AutoLayoutbyExample/AutoLayoutbyExample.html#//apple_ref/doc/uid/TP40010853-CH5-SW2</a></p>
  
  <p>basic idea is to make a container view outside the scroll view to make sure the labels can fill the scroll view no matter what direction it is.</p>
  
  <p>here is the hierarchy and constraint:
  <img src="https://i.stack.imgur.com/RsUrk.png" alt="enter image description here"></p>
  
  <p>and the portrait mode works well:
  <img src="https://i.stack.imgur.com/NNhZt.png" alt="enter image description here"></p>
  
  <p><strong>but when it change to landscape mode some wired gap pops up!</strong>
  <img src="https://i.stack.imgur.com/I3kPH.png" alt="enter image description here"></p>
  
  <p>and the more text i put in the label the higher gap i got!
  my question is what should i do to kill those gap?
  please give me some explicit solution or just give me an example, thank you!</p>
  
  <p>and i am using autolayout in ios7, so some solution without coding are preferred!</p>