Can Xcode Document-based app be set to always open in a new tab

Question

I have an macOS xcode swiftui document-based app. I can see that if I, "view->show tab bar" in the app, I get multiple tabs for free. However, if I do a "file open ...", it creates a new window. Now I eventually found that holding down option when selecting the file will open it in a new tab of an existing window. Does anyone know if it is possible to configure a document-based app to always open in a new tab rather than a new window each time?

Answer 1

Set window.tabbingMode to preferred in makeWindowControllers().

override func makeWindowControllers() {
    // Create the SwiftUI view that provides the window contents.
    let contentView = ContentView()

    // Create the window and set the content view.
    let window = NSWindow(
        contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
        styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
        backing: .buffered, defer: false)
    window.isReleasedWhenClosed = false
    window.center()
    window.contentView = NSHostingView(rootView: contentView)
    
    window.tabbingMode = .preferred // open new document in tab
    
    let windowController = NSWindowController(window: window)
    self.addWindowController(windowController)
}