Respond to key press events in SwiftUI

Question

I want to respond to key presses, such as the esc key on macOS/OSX, and when using an external keyboard on iPad. How can I do this?

I have thought of using @available/#available with SwiftUI's onExitCommand, which looked very promising, but unfortunately that is only for macOS/OSX. How can I respond to key presses in SwiftUI for more than just macOS/OSX?

Answer 1

Update: SwiftUI 2 now has .keyboardShortcut(_:modifiers:).

---

OLD ANSWER:

With thanks to @Asperi to pointing me in the right direction, I have now managed to get this working.

The solution was to use UIKeyCommand. Here is what I did, but you can adapt it differently depending on your situation.

I have an @EnvironmentObject called AppState, which helps me set the delegate, so they keyboard input can be different depending on the view currently showing.

protocol KeyInput {
    
    func onKeyPress(_ key: String)
}


class KeyInputController<Content: View>: UIHostingController<Content> {
    
    private let state: AppState
    
    init(rootView: Content, state: AppState) {
        self.state = state
        super.init(rootView: rootView)
    }
    @objc required dynamic init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    override func becomeFirstResponder() -> Bool {
        true
    }
    
    override var keyCommands: [UIKeyCommand]? {
        switch state.current {
        case .usingApp:
            return [
                UIKeyCommand(input: UIKeyCommand.inputEscape, modifierFlags: [], action: #selector(keyPressed(_:)))
            ]
            
        default:
            return nil
        }
    }
    
    @objc private func keyPressed(_ sender: UIKeyCommand) {
        guard let key = sender.input else { return }
        state.delegate?.onKeyPress(key)
    }
}

AppState (@EnvironmentObject):

class AppState: ObservableObject {

    var delegate: KeyInput?
    /* ... */
}

And the scene delegate looks something like:

let stateObject = AppState()
let contentView = ContentView()
    .environmentObject(stateObject)

// Use a UIHostingController as window root view controller.
if let windowScene = scene as? UIWindowScene {
    let window = UIWindow(windowScene: windowScene)
    window.rootViewController = KeyInputController(rootView: contentView, state: stateObject)

    /* ... */
}

This makes it really easy to now add functionality depending on the keys pressed.

Conform to KeyInput, e.g.:

struct ContentView: View, KeyInput {

    /* ... */

    var body: some View {
        Text("Hello world!")
            .onAppear {
                self.state.delegate = self
            }
    }
    
    func onKeyPress(_ key: String) {
        print(key)
        guard key == UIKeyCommand.inputEscape else { return }
        // esc key was pressed
        /* ... */
    }
}