Authoring Visual Studio Extensions

using System;
using System.ComponentModel.Design;
using Microsoft.VisualStudio.Shell;
using Task = System.Threading.Tasks.Task;

namespace HelloWorldExtension
{
    internal sealed class HelloWorldCommand
    {
        public const int CommandId = 0x0100;
        public static readonly Guid CommandSet = new Guid("d3f8c45a-7b3e-4b2a-9c6e-1a2b345cdef0");

        private readonly AsyncPackage package;

        private HelloWorldCommand(AsyncPackage package, OleMenuCommandService commandService)
        {
            this.package = package ?? throw new ArgumentNullException(nameof(package));
            var cmdID = new CommandID(CommandSet, CommandId);
            var menuItem = new MenuCommand(Execute, cmdID);
            commandService.AddCommand(menuItem);
        }

        public static async Task InitializeAsync(AsyncPackage package)
        {
            await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync(package.DisposalToken);
            var commandService = await package.GetServiceAsync(typeof(IMenuCommandService)) as OleMenuCommandService;
            new HelloWorldCommand(package, commandService);
        }

        private void Execute(object sender, EventArgs e)
        {
            ThreadHelper.ThrowIfNotOnUIThread();
            VsShellUtilities.ShowMessageBox(
                this.package,
                "Hello, World! Your extension is working.",
                "Hello World",
                OLEMSGICON.INFO,
                OLEMSGBUTTON.OK,
                OLEMSGDEFBUTTON.DEFAULT);
        }
    }
}