How do I create a real-time Excel automation add-in in C# using RtdServer?

Question

I was tasked with writing a real-time Excel automation add-in in C# using RtdServer for work. I relied heavily on the knowledge that I came across in Stack Overflow. I have decide to express my thanks by writing up a how to document that ties together all that I have learned. Kenny Kerr's Excel RTD Servers: Minimal C# Implementation article helped me get started. I found comments by Mike Rosenblum and Govert especially helpful.

Answer 1

(As an alternative to the approach described below you should consider using Excel-DNA. Excel-DNA allows you to build a registration-free RTD server. COM registration requires administrative privileges which may lead to installation headaches. That being said, the code below works fine.)

To create a real-time Excel automation add-in in C# using RtdServer:

1) Create a C# class library project in Visual Studio and enter the following:

using System;
using System.Threading;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using Microsoft.Office.Interop.Excel;

namespace StackOverflow
{
    public class Countdown
    {
        public int CurrentValue { get; set; }
    }

    [Guid("EBD9B4A9-3E17-45F0-A1C9-E134043923D3")]
    [ProgId("StackOverflow.RtdServer.ProgId")]
    public class RtdServer : IRtdServer
    {
        private readonly Dictionary<int, Countdown> _topics = new Dictionary<int, Countdown>();
        private Timer _timer;

        public int ServerStart(IRTDUpdateEvent rtdUpdateEvent)
        {
            _timer = new Timer(delegate { rtdUpdateEvent.UpdateNotify(); }, null, TimeSpan.Zero, TimeSpan.FromSeconds(5));
            return 1;
        }

        public object ConnectData(int topicId, ref Array strings, ref bool getNewValues)
        {
            var start = Convert.ToInt32(strings.GetValue(0).ToString());
            getNewValues = true;

            _topics[topicId] = new Countdown { CurrentValue = start };

            return start;
        }

        public Array RefreshData(ref int topicCount)
        {
            var data = new object[2, _topics.Count];
            var index = 0;

            foreach (var entry in _topics)
            {
                --entry.Value.CurrentValue;
                data[0, index] = entry.Key;
                data[1, index] = entry.Value.CurrentValue;
                ++index;
            }

            topicCount = _topics.Count;

            return data;
        }

        public void DisconnectData(int topicId)
        {
            _topics.Remove(topicId);
        }

        public int Heartbeat() { return 1; }

        public void ServerTerminate() { _timer.Dispose(); }

        [ComRegisterFunctionAttribute]
        public static void RegisterFunction(Type t)
        {
            Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(@"CLSID\{" + t.GUID.ToString().ToUpper() + @"}\Programmable");
            var key = Microsoft.Win32.Registry.ClassesRoot.OpenSubKey(@"CLSID\{" + t.GUID.ToString().ToUpper() + @"}\InprocServer32", true);
            if (key != null)
                key.SetValue("", System.Environment.SystemDirectory + @"\mscoree.dll", Microsoft.Win32.RegistryValueKind.String);
        }

        [ComUnregisterFunctionAttribute]
        public static void UnregisterFunction(Type t)
        {
            Microsoft.Win32.Registry.ClassesRoot.DeleteSubKey(@"CLSID\{" + t.GUID.ToString().ToUpper() + @"}\Programmable");
        }
    }
}

2) Right click on the project and Add > New Item... > Installer Class. Switch to code view and enter the following:

using System.Collections;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace StackOverflow
{
    [RunInstaller(true)]
    public partial class RtdServerInstaller : System.Configuration.Install.Installer
    {
        public RtdServerInstaller()
        {
            InitializeComponent();
        }

        [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
        public override void Commit(IDictionary savedState)
        {
            base.Commit(savedState);

            var registrationServices = new RegistrationServices();
            if (registrationServices.RegisterAssembly(GetType().Assembly, AssemblyRegistrationFlags.SetCodeBase))
                Trace.TraceInformation("Types registered successfully");
            else
                Trace.TraceError("Unable to register types");
        }

        [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand)]
        public override void Install(IDictionary stateSaver)
        {
            base.Install(stateSaver);

            var registrationServices = new RegistrationServices();
            if (registrationServices.RegisterAssembly(GetType().Assembly, AssemblyRegistrationFlags.SetCodeBase))
                Trace.TraceInformation("Types registered successfully");
            else
                Trace.TraceError("Unable to register types");
        }

        public override void Uninstall(IDictionary savedState)
        {
            var registrationServices = new RegistrationServices();
            if (registrationServices.UnregisterAssembly(GetType().Assembly))
                Trace.TraceInformation("Types unregistered successfully");
            else
                Trace.TraceError("Unable to unregister types");

            base.Uninstall(savedState);
        }
    }
}

3) Right click on the project Properties and check off the following: Application > Assembly Information... > Make assembly COM-Visible and Build > Register for COM Interop

3.1) Right click on the project Add Reference... > .NET tab > Microsoft.Office.Interop.Excel

4) Build Solution (F6)

5) Run Excel. Go to Excel Options > Add-Ins > Manage Excel Add-Ins > Automation and select "StackOverflow.RtdServer"

6) Enter "=RTD("StackOverflow.RtdServer.ProgId",,200)" into a cell.

7) Cross your fingers and hope that it works!