Adding a Menu Bar extra (icon) to a Flutter macOS app

AppDelegate.swift

import Cocoa
import FlutterMacOS
import SwiftUI

// Relevant blog post: https://blog.whidev.com/menu-bar-extra-flutter-macos-app

struct Shortcut {
    var combination: String
    var description: String
    var createdAt: Int
}

@NSApplicationMain
class AppDelegate: FlutterAppDelegate {
    var statusBar: NSStatusItem?
    var flutterViewController: FlutterViewController?
    var popover = NSPopover()
    
    override func applicationWillFinishLaunching(_ notification: Notification) {
        let flutterViewController = NSApplication.shared.windows.first?.contentViewController as? FlutterViewController
        self.flutterViewController = flutterViewController
    }
    
    override func applicationDidFinishLaunching(_ aNotification: Notification) {
        statusBar = NSStatusBar.system.statusItem(withLength: CGFloat(NSStatusItem.variableLength))
        if let button = statusBar?.button {
            button.image = NSImage(named: "MenuBarIcon")
            button.action = #selector(togglePopover(_:))
        }
    }
    
    @objc func togglePopover(_ sender: AnyObject) {
        if let button = statusBar?.button {
            if popover.isShown {
                popover.performClose(sender)
            } else {
                let frontmostAppName = NSWorkspace.shared.frontmostApplication?.localizedName
                if let flutterViewController = flutterViewController {
                    let statusBarChannel = FlutterMethodChannel(name: "com.sk.statusbar", binaryMessenger: flutterViewController.engine.binaryMessenger)
                    statusBarChannel.invokeMethod("getShortcutsForApp", arguments: frontmostAppName) { (result: Any?) in
                        if let error = result as? FlutterError {
                            print("Error Occurred: \(error.message ?? "")")
                        } else if let shortcutsJSON = result as? [[String: Any]] {
                            var shortcuts: [Shortcut] = []
                            
                            shortcutsJSON.forEach { item in
                                if let combination = item["combination"] as? String,
                                   let createdAt = item["createdAt"] as? Int,
                                   let description = item["description"] as? String {
                                    shortcuts.append(Shortcut(combination: combination,  description: description, createdAt: createdAt ))
                                }
                            }
                            if #available(macOS 10.15, *) {
                                let contentView = PopoverContentView(appName: frontmostAppName!, shortcuts: shortcuts)
                                let popover = NSPopover()
                                popover.contentSize = NSSize(width: 300, height: 400)
                                popover.contentViewController = NSHostingController(rootView: contentView)
                                popover.behavior = .transient
                                popover.show(relativeTo: button.bounds, of: button, preferredEdge: NSRectEdge.minY)
                                self.popover = popover
                            }
                        }
                    }
                }
            }
        }
    }
}

struct PopoverContentView: View {
    var appName: String
    var shortcuts: [Shortcut]
    
    init(appName: String, shortcuts: [Shortcut]) {
        self.appName = appName
        self.shortcuts = shortcuts
    }
    
    var body: some View {
        ZStack {
            VStack{
                Text("\(appName) shortcuts:")
                    .font(.headline)
                    .padding()
                
                if shortcuts.isEmpty {
                    VStack {
                        Text("No shortcuts saved for \(appName).").font(.headline)
                        Text("Go to Shortcut Keeper to \n add shortcuts for this app.")
                            .multilineTextAlignment(.center).padding()
                    }.padding()
                } else {
                    shortcutsList
                }
            }
        }
    }
    
    var shortcutsList: some View {
        List(shortcuts, id: \.createdAt) { item in
            HStack {
                Text(item.combination)
                    .font(.subheadline)
                    .bold()
                    .frame(maxWidth: .infinity, alignment: .leading)
                Text(item.description)
                    .font(.subheadline)
                    .frame(maxWidth: .infinity, alignment: .leading)
            }
        }
    }
}

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  const platform = MethodChannel('com.sk.statusbar');
  platform.setMethodCallHandler((MethodCall call) async {
    if (call.method == "getShortcutsForApp") {
      try {
        String appName = call.arguments.toString();
        //final shortcutsList = getShortcutsForApp(appName);
        final shortcutsList = [
          {
            "combination": "Shift-Command-I",
            "description": "Open Developer Tools",
            "app": "Microsoft Visual Studio Code",
            "createdAt": 1686733115884
          },
          {
            "combination": "Control-Command-T",
            "description": "Tile tabs vertically",
            "app": "Microsoft Visual Studio Code",
            "createdAt": 1686733115883
          },
          {
            "combination": "Control-Shift-Command-T",
            "description": "Tile tabs horizontally",
            "app": "Microsoft Visual Studio Code",
            "createdAt": 1686733115882
          }
        ];
        return shortcutsList;
      } catch (e, stackTrace) {
        debugPrint("Error Occurred: $e\nStackTrace: $stackTrace");
        return null;
      }
    }
  });
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter macOS with menu bar icon',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter macOS with menu bar icon'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), 
    );
  }
}