Method Overloading in Excel COM Interop

Question

I am having a lot of troubles with method overloading here and have no idea why only one method gets called each time regardless the number of parameters I pass into. Below is the sample code.

[ClassInterface(ClassInterfaceType.AutoDual), ComVisible(true)]
public class myClass
{
    //constructor
    public myClass() {}

    //base method
    public string myfunction(string id, string pk) {return results;}

    //overloading method 1
    public string myfunction(string id, string pk, string param1) { return results;}

    //overloading method 2
    public string myfunction(string id, string pk, string param1, string param2) {return results;}



    [ComRegisterFunctionAttribute]
        public static void RegisterFunction(Type type)
        {

            Registry.ClassesRoot.CreateSubKey(
              GetSubKeyName(type, "Programmable"));
            RegistryKey key = Registry.ClassesRoot.OpenSubKey(
              GetSubKeyName(type, "InprocServer32"), true);
            key.SetValue("",
              System.Environment.SystemDirectory + @"\mscoree.dll",
              RegistryValueKind.String);
        }
        [ComUnregisterFunctionAttribute]
        public static void UnregisterFunction(Type type)
        {

            Registry.ClassesRoot.DeleteSubKey(
              GetSubKeyName(type, "Programmable"), false);
        }
        private static string GetSubKeyName(Type type,
          string subKeyName)
        {
            System.Text.StringBuilder s =
              new System.Text.StringBuilder();
            s.Append(@"CLSID\{");
            s.Append(type.GUID.ToString().ToUpper());
            s.Append(@"}\");
            s.Append(subKeyName);
            return s.ToString();
        }

}

So when I tested it in Excel, the base method worked fine and I could get the expected value. However, it would fail if I tried the rest two functions using method overloading. They simply didn't get called for some reason. Am I missing something in the code? Can anyone help me please? Thanks very much.

Edit:

Through some experiments, it occurs to me that there only 1 method can be recognized, which normally is the first method. So if I swap the order between base method and overloading method 1, the overloading method 1 will be called instead of the base method. Looks like the whole class just gets stuck in the first method and wouldn't go on.

Answer 1

Excelfriend, you can't polymorphize a a worksheet function. A worksheet function called, say, GETSALESFORWEEK can only have one entry point. If you provide two, say GETSALESFORWEEK(int WeekNumber) and GETSALESFORWEEK(string WeekName) then Excel 2007 will expose these functions as GETSALESFORWEEK and GETSALESFORWEEK_2.

Source: http://blogs.msdn.com/b/gabhan_berry/archive/2008/04/07/writing-custom-excel-worksheet-functions-in-c_2d00_sharp.aspx

Well I guess that answers my questions. Sadly, no method overloading for custom Excel functions :(

Solution:

[ClassInterface(ClassInterfaceType.AutoDual), ComVisible(true)]
public class myClass
{
    //constructor
    public myClass() {}

    //base method
    /**public string myfunction(string id, string pk) {return results;}**/

    //overloading method 1
    /**public string myfunction(string id, string pk, string param1) { return results;}**/

    //just use 1 method, but make the last two arguments optional by setting default values
    public string myfunction(string id, string pk, string param1 = "", string param2 = "") {return results;}

    [ComRegisterFunctionAttribute]
    public static void RegisterFunction(Type type)
    {
        Registry.ClassesRoot.CreateSubKey(
          GetSubKeyName(type, "Programmable"));
        RegistryKey key = Registry.ClassesRoot.OpenSubKey(
          GetSubKeyName(type, "InprocServer32"), true);
        key.SetValue("",
          System.Environment.SystemDirectory + @"\mscoree.dll",
          RegistryValueKind.String);
    }

    [ComUnregisterFunctionAttribute]
    public static void UnregisterFunction(Type type)
    {
        Registry.ClassesRoot.DeleteSubKey(
          GetSubKeyName(type, "Programmable"), false);
    }

    private static string GetSubKeyName(Type type, string subKeyName)
    {
        System.Text.StringBuilder s = new System.Text.StringBuilder();
        s.Append(@"CLSID\{");
        s.Append(type.GUID.ToString().ToUpper());
        s.Append(@"}\");
        s.Append(subKeyName);
        return s.ToString();
    }
}