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How to detect device rotation

Paul Hudson    @twostraws   

Updated for Xcode 12.5

SwiftUI doesn’t have a built-in way to detect the user rotating their device between portrait and landscape orientation, but we can make one using a custom modifier by responding to the UIDevice.orientationDidChangeNotification notification.

First, we’re going to create a custom view modifier that watches for orientation changes and runs a callback function when it happens. It’s not required, but we’re going to make the callback accept a UIDeviceOrientation as its only parameter, just in case you need to know the current orientation.

Add this code now:

struct DeviceRotationViewModifier: ViewModifier {
    let action: (UIDeviceOrientation) -> Void

    func body(content: Content) -> some View {
        content
            .onAppear()
            .onReceive(NotificationCenter.default.publisher(for: UIDevice.orientationDidChangeNotification)) { _ in
                action(UIDevice.current.orientation)
            }
    }
}

Tip: At the time of writing view modifiers do not work with onReceive() unless you first add onAppear(), which is why it appears above. Yes, it’s empty, but it acts as a workaround for the problem.

Second, we’re going to wrap that view modifier up in a View extension so that it’s easier to call:

extension View {
    func onRotate(perform action: @escaping (UIDeviceOrientation) -> Void) -> some View {
        self.modifier(DeviceRotationViewModifier(action: action))
    }
}

And now

struct ContentView: View {
    @State private var orientation = UIDeviceOrientation.unknown

    var body: some View {
        Group {
            if orientation.isPortrait {
                Text("Portrait")
            } else if orientation.isLandscape {
                Text("Landscape")
            } else if orientation.isFlat {
                Text("Flat")
            } else {
                Text("Unknown")
            }
        }
        .onRotate { newOrientation in
            orientation = newOrientation
        }
    }
}

Please remember that device orientation isn’t quite as useful as you might expect. Yes, on iPhone a landscape orientation means you have more horizontal space than vertical, but on iPad it’s possible for your app to be running in landscape while in split-screen mode – technically the whole screen still has a larger width than height, but the actual space allocated to our app is only a small slice of that width.

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