Dynamic Delegate Registration

In come cases one might want to implement some kind of function wrapper or transformation at runtime. E.g. automatically wrapping and registering async Task / Rx functions.

The latest check-ins for Excel-DNA (check-in 79681 and eventually version 0.32) implement the support required to do this.

The key method that has been added is ExcelIntegration.RegisterDelegates(...), which allows you to pass in a list of delegates, together with lists of ExcelFunction / ExcelArgument attributes. Because this takes Delegates and not just MethodInfos, you can easily wrap an existing method with to include your processing code for the optional / default values.

A useful helper that complements this is ExcelIntegration.GetExportedAssemblies() which returns the Assemblies that were considered for registration by Excel-DNA - either from ExternalLibrary tags in the .dna file or from runtime-compiled source projects inside the .dna file.

The basic idea would be:

In your AutoOpen, call some kind of UpdateRegistrations() which works like this:

1. Get all the methods you’re interested in via Reflection (from the assemblies returned by ExcelIntegration.GetExportedAssemblies()).
2. Build delegates using lambda expressions that add the optional handling (or using the Expression Tree API for even more control).
3. Register the delegates with the right attributes via ExcelIntegration.RegisterDelegates.

This code should be a start:

<DnaLibrary Name="Dynamic Function Tests" Language="C#" RuntimeVersion="v4.0">
<Reference Name="System.Windows.Forms" />
<![CDATA[
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Windows.Forms;
using ExcelDna.Integration;

public class TestAddIn : IExcelAddIn
{
    public void AutoOpen()
    {
        try
        {
            MessageBox.Show("In AutoOpen");

            var helloDel = MakeDelegate("Hello ");
            var byeDel = MakeDelegate("Goodbye ");

            var helloAtt = new ExcelFunctionAttribute
            {
                Name = "delHello",
            };
            var helloArgAtt = new ExcelArgumentAttribute
            {
                Name = "theName",
                Description = "is the name of the person to say 'Hello' to."
            };

            var byeAtt = new ExcelFunctionAttribute
            {
                Name = "delGoodbye",
            };
            var byeArgAtt = new ExcelArgumentAttribute
            {
                Name = "theName",
                Description = "is the name of the person to say 'Goodbye' to."
            };

            var add3Del = MakeAddNumber(3);
            var add3Att = new ExcelFunctionAttribute
            {
                Name = "delAdd3",
                Description = "Adds 3 to a number",
                IsThreadSafe = true,
                IsExceptionSafe = true
            };
            var add3ArgAtt = new ExcelArgumentAttribute
            {
                Name = "theNumber",
                Description = "is the number to which the adding is done."
            };

            ExcelIntegration.RegisterDelegates(
              new List<Delegate> { helloDel, byeDel, add3Del },
              new List<object>   { helloAtt, byeAtt, add3Att },
              new List<List<object>> { new List<object> {helloArgAtt},
                                       new List<object> {byeArgAtt},
                                       new List<object> {add3ArgAtt},
                                     } );
        }
        catch (Exception ex)
        {
              MessageBox.Show(ex.ToString());
        }
    }

    public void AutoClose() {}

    static Func<string, string> MakeDelegate(string sayWhat)
    {
        Func<string, string> saySomethingToName = name => sayWhat + name;
        return saySomethingToName;
    }

    static Func<double, object> MakeAddNumber(double numberToAdd)
    {
      return x =>
      {
        try
        {
          return x + numberToAdd;
        }
        catch (Exception ex)
        {
          return double.NaN;
        }
      };
    }
}

]]>
</DnaLibrary>