SwiftUI macOS app with `App` protocol deep linking opens new app instance

Question

This is in a SwiftUI macOS app using the new App protocol and @main.

Usage flow:

• User launches app and clicks a button which opens a particular webpage
• Webpage eventually redirects to the app's URL scheme, opening the app and invoking onOpenURL(_:)

Expected behaviour: The deep link is sent to the existing, currently open app instance

Actual behaviour: A new app instance is launched, causing two instances of the app to be active

Note: There isn't really any code to add since the problem is just dependent on adding a URL scheme to the app and having a webpage go to it.

Aerophyte

Running two instances of an app isn’t possible on macOS, unless you have multiple copies of the app installed (e.g., one in Applications and another in Xcode’s build directory). If you have both apps running, try right-clicking each one and selecting “Show in finder”, which will show you where the app is located. If there’s a second app installed, delete it. – Incorporeal

Answer 1

onOpenURL(_:) is not actually launching a new app instance, it is creating a new window within the existing instance. The documentation would suggest this only happens on macOS (because iOS only supports a single window).

You need to use the .handlesExternalEvents(preferring:allowing:) modifier on a higher order view. Calling handlesExternalEvents will override the default behaviour which is what is creating the new window in your app on macOS. Something like:

@main
struct myApp: App {    
    var body: some Scene {
        WindowGroup {
            ContentView()
            .handlesExternalEvents(preferring: ["myscheme"], allowing: ["myscheme"])
        }
    }
}

An then in a child view (e.g. ContentView()):

var body: some View {
    VStack {
        // your UI
    }
    .onOpenUrl{ url in
        // do something with the deep link url
    }
}

Cocoon