UISplitView popup button not showing when put in a view controller

I took the apple standard example, MultiDetailView and just added a generic view controller in between the app delegate and the split view controller.

window > view controller > UISplitViewController

In terms of code, I just change from

[window addSubview:splitView.view];

to

[window addSubview:viewController.view];

and within the generic开发者_StackOverflow中文版 view controller subclass

[self.view addSubview:splitView.view];

However, the act of doing so makes the standard left popup button to disappear in portrait view.

How do I get the standard left popup button to appear again?