How do I use auto layout to start a view in the half of its superview?

Question

I have a view inside a view:

+--------------+
|              |
|       +-----+|
|       |     ||
|       +-----+|
+--------------+

I’d like the inner view to always start right in the middle of the outer view horizontally, and span the whole remaining half to the right edge:

innerView.frame.size.width = outerView.frame.size.width/2;
innerView.frame.origin.x = outerView.frame.size.width/2;

How can I express that using auto layout?

Answer 1

You actually can do this in IB/Storyboards as far back as Xcode 5.1 (potentially earlier)

1. Create a width constraint between the view and the super view
2. Set it's relationship to "Equal"
3. Set it's constant to "0"
4. Set it's multiplier to "2:1" or "1:2" (depending on item order in the constraint)

IB, apparently, only allows multipliers to be set to integers or ratios, not floating point numbers. Here's a screen cap for more clarity

Note: if "First Item" and "Second Item" are flipped, the ratio is "2:1"