Why detailViewController is not in UISplitViewController.viewControllers anymore?

Question

I use UISplitViewController to build my app. Both the master view controller and detail view controller are UINavigationControllers, as illustrated in the Figure.

In the viewDidLoad() functions of both master vc and detail vc, the following code is inserted:

    println(self.splitViewController!.viewControllers.count)
    for vc in self.splitViewController!.viewControllers {
        println(vc.hashValue)
    }

The result is:

master vc.viewDidLoad()

2
140692681984032
140692680836304

detaiVC.viewDidLoad()

1
140692681984032

It turns out that in detaiVC.viewDidLoad(), detailVC is not in splitViewController.viewControllers any more. Why?

Answer 1

When running your app in a compact width, the splitviewcontroller will be compacted. ie the var viewControllers property only contains 1 view controller.

From the documentation:

When the split view interface is expanded, this property contains two view controllers; when it is collapsed, this property contains only one view controller.

https://developer.apple.com/library/ios/documentation/UIKit/Reference/UISplitViewController_class/#//apple_ref/occ/instp/UISplitViewController/viewControllers