Initial window with no width in application using Storyboards

Question

I am trying to understand Storyboard in XCode. I have created a new Mac OS X Application from template and defined a simple Storyboard, like in the following image:

The problem is that when I run the application, my window looks like this:

I have to resize it to see RIGHT and LEFT part of vertical split view. I have defined height and with of my window so I don't know why is this happening and I really don't know why is this window correctly shown with view controller below instead of split view controller.

What I am doing wrong with split view controller?

Answer 1

A solution is to add width constraints with a minimum width to the views in each side of the SplitView.

I got the idea from this answer to a similar question.