Open UISplitViewController to Master View rather than Detail

Swift

UISplitViewController display master view above detail in portrait orientation is not about showing the Master view, it is about presenting the Detail view in full width, underneath the Master view.

UISplitViewController in portrait on iPhone shows detail VC instead of master is about the principle of the collapse mechanism.

This present answer addresses:

• Master → Detail (Compact width)
  • iPhone 4s, 5, 5s, SE, 6, 6s, 7 (any orientation)
  • iPod Touch
  • any iPhone Plus (portrait)
• side-by-side (all other sizes)
  • iPad
  • any iPhone Plus (landscape)

You must set preferredDisplayMode. You would want is .primaryVisible if it existed! Using .allVisible, iOS picks Detail if only 1 view fits (Compact width); in that size, the code below will pick Master.

The trick is to change both the preferredDisplayMode to .allVisible and to return true in collapseSecondary:onto.

class PrimarySplitViewController: UISplitViewController,
                                  UISplitViewControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.delegate = self
        self.preferredDisplayMode = .allVisible
    }

    func splitViewController(
             _ splitViewController: UISplitViewController,
             collapseSecondary secondaryViewController: UIViewController,
             onto primaryViewController: UIViewController) -> Bool {
        // Return true to prevent UIKit from applying its default behavior
        return true 
    }
}

iOS 14

I wasn't getting a callback for splitViewController(_:collapseSecondary:onto:) and instead used the following new method.

func splitViewController(_ svc: UISplitViewController, topColumnForCollapsingToProposedTopColumn proposedTopColumn: UISplitViewController.Column) -> UISplitViewController.Column {
    return .primary
}