Adding an "Open in New Window" Feature to SwiftUI on macOS

What is this?

A guide to opening a new window using SwiftUI when developing an app for macOS.

Implementation example

Environment

Apple Silicon M1 MacBook Air
16 Gb
macOS Sequoia 15.0
Xcode Version 16.0 (16A242d)

Steps

This time we'll build something where tapping a button in ContentView.swift opens PopupWindow.swift.

Set up the window

First, set up the window you want to open.
Here I'm using an arbitrary file name, PopupWindow.swift.

//
//  PopupWindow.swift
//  sample
//
//

import SwiftUI
import AVKit

struct PopupWindow: View {


    var body: some View {
        VStack {
           Text("ポップアップウィンドウです")
        }
        .padding()
        .frame(minWidth: 440, minHeight: 480)
    }
}

#Preview {
    PopupWindow()
}

Add a WindowGroup

Open the AppName App.swift file that gets created automatically when you create a project.

Add the following to it.

//
//  アプリ名App.swift
//  sample
//
//

import SwiftUI

@main
struct FolderCustomizerApp: App {

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        // ここを追記した
        WindowGroup(id: "popup") {
            PopupWindow()
        }
    }
}

Add the button

Finally, add a button to ContentView.Swift.

省略

Button(action: {
    openWindow(id: "popup")
    }) {
    Label("help", systemImage: "keyboard.macwindow")
}

省略

And that's it! This should work now.

If what you're actually after is expanding multiple pieces of info in a sidebar when clicked, check out Apple's official session on the topic — it's explained clearly with sample code:
https://developer.apple.com/jp/videos/play/wwdc2022/10061/