How to lock orientation in portrait for an iPhone SwiftUI app running on iPad?

Question

I have a SwiftUI iPhone-only app with its orientation locked in portrait, which works great. However, when the same app is run on an iPad (in emulation mode; iPad is not a target) the lock has no effect: the UI rotates with the device, which is unintended as it breaks the UI. It fails in the simulator and on an actual device.

I can reproduce this issue using an empty SwiftUI project with only a single view:

struct ContentView: View {
    var body: some View {
        Text("Hello, world!")
    }
}

iPhone works as expected:

iPad does not respect orientation lock:

I have the following in my Info.plist, but no success. The UI still rotates on the iPad.

<key>UISupportedInterfaceOrientations</key>
<array>
    <string>UIInterfaceOrientationPortrait</string>
</array>
<key>UISupportedInterfaceOrientations~ipad</key>
<array>
    <string>UIInterfaceOrientationPortrait</string>
</array>

Then I defined an AppDelegate. Still no success, the UI keeps rotating on the iPad.

class AppDelegate: NSObject, UIApplicationDelegate {
    func application(_ application: UIApplication, supportedInterfaceOrientationsFor window: UIWindow?) -> UIInterfaceOrientationMask {
        return UIInterfaceOrientationMask.portrait
    }
}

@main
struct orientationApp: App {
    @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

What is interesting:

• When I enable iPad as a target the orientation lock works out of the box. However, I do not want to offer the app for the iPad. I just want to fix the UI for users who deliberately install iPhone apps on their iPad.
• When I test the AppDelegate approach on an iPhone it works even if I allow all device orientations in Info.plist, so it seems to do the right thing (just not on the iPad).

I'm using Xcode 12.5 and Swift 5.

Answer 1

Unticking Supports multiple windows solved the problem for me