C # COM implements enum without reference MSCORLIB

"The thing is, I don't want the C ++ client application to import mscorlib.tlb."

This is not possible as you are creating your COM class with .NET, which automatically brings mscorlib.tlb and mscoree.dll into play. Try this with a simple object that can only add two integers.

As Hans Passant pointed out, you don't need an interface at all IEnumVARIANT

. Any COM collection must be based on a C # collection, for example List<T>

. This C # collection has a method GetEnumeration()

that spits out an object IEnumeration

that serves as a IEnumVARIANT

COM. All you have to do is include IEnumerator GetEnumerator();

in the interface and delegate the implementation to GetEnumeration()

the C # collection method .

I am showing this in a complete example. Consider a class bank that manages a set of accounts. I need points for the Bank, Account and AllAccounts collection.

I'll start with the key account AllAccounts:

//AllAccounts.cs:
using System;
using System.Collections;
using System.Runtime.InteropServices;

namespace BankServerCSharp
{
  [ComVisible(true)]  // This is mandatory.
  [InterfaceType(ComInterfaceType.InterfaceIsDual)]
  public interface IAllAccounts
  {
    int Count{ get; }

    [DispId(0)]
    IAccount Item(int i);

    [DispId(-4)]
    IEnumerator GetEnumerator();

    Account AddAccount();

    void RemoveAccount(int i);

    void ClearAllAccounts();
  }

  [ComVisible(true)]  // This is mandatory.
  [ClassInterface(ClassInterfaceType.None)]
  public class AllAccounts:IAllAccounts 
  {
    private AllAccounts(){ } // private constructor, coclass noncreatable
    private List<IAccount> Al = new List<IAccount>();
    public static AllAccounts MakeAllAccounts() { return new AllAccounts(); }
    //public, but not exposed to COM

    public IEnumerator GetEnumerator() { return Al.GetEnumerator();  }

    public int Count { get { return Al.Count; } }

    public IAccount Item(int i)  { return (IAccount)Al[i - 1];  }

    public Account AddAccount() { Account acc = Account.MakeAccount();
                                        Al.Add(acc); return acc; }

    public void RemoveAccount(int i) {  Al.RemoveAt(i - 1);  }

    public void ClearAllAccounts() { Al.Clear(); }

  }
}

      

        
        
        
      

    

Values DispId

equal to 0 and -4 are required for the default Item

method and for the method GetEnumerator()

. Two other files:

Account.cs:
using System.Runtime.InteropServices;

namespace BankServerCSharp
{
  [ComVisible(true)]  // This is mandatory.
  [InterfaceType(ComInterfaceType.InterfaceIsDual)]
  public interface IAccount
  {
    double Balance { get; } // A property
    void Deposit(double b); // A method
  }

  [ComVisible(true)]  // This is mandatory.
  [ClassInterface(ClassInterfaceType.None)]
  public class Account:IAccount
  {
    private double mBalance = 0;
    private Account() { }     // private constructor, coclass noncreatable

    public static Account MakeAccount() { return new Account(); }
    //MakeAccount is not exposed to COM, but can be used by other classes

    public double Balance  { get {  return mBalance; } }
    public void Deposit(double b) { mBalance += b; }
  }
}

Bank.cs:
using System.Runtime.InteropServices;

namespace BankServerCSharp
{
  [ComVisible(true)]  // This is mandatory.
  [InterfaceType(ComInterfaceType.InterfaceIsDual)]
  public interface IBank { IAllAccounts Accounts { get; }  }

  [ComVisible(true)]  // This is mandatory.
  [ClassInterface(ClassInterfaceType.None)]
  public class Bank:IBank
  {
    private readonly AllAccounts All;
    public Bank() {  All = AllAccounts.MakeAllAccounts(); } 
    public IAllAccounts Accounts {  get { return All; } }
  }
}

      

        
        
        
      

    

You must register the server with the x64 version of Regasm.

Server test with C ++:

#include "stdafx.h"
#include <string>
#import  "D:\Aktuell\CSharpProjects\BankServerCSharp\BankServerCSharp\bin\Release\BankServerCSharp.tlb"
//this is the path of my C# project bin\Release folder
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_errorex(x, nullptr, ID_NULL);}
int main()
{
  try
  {
    TESTHR(CoInitialize(0));
    BankServerCSharp::IBankPtr BankPtr = nullptr;
    TESTHR(BankPtr.CreateInstance("BankServerCSharp.Bank"));
    BankServerCSharp::IAllAccountsPtr AllPtr = BankPtr->Accounts;
    BankServerCSharp::IAccountPtr FirstAccountPtr = AllPtr->AddAccount();
    TESTHR(FirstAccountPtr->Deposit(47.11));
    AllPtr->AddAccount();
    TESTHR(AllPtr->Item[2]->Deposit(4711));

    CStringW out, add;
    for (int i = 1; i <= AllPtr->Count; i++)
    {
      add.Format(L"Balance of account %d: %.2f.\n", i, AllPtr->Item[i]->Balance);
      out += add;
    }

    out += L"\n";
    AllPtr->RemoveAccount(1);
    for (int i = 1; i <= AllPtr->Count; i++)
    {
      add.Format(L"Balance of account %d: %.2f.\n", i, AllPtr->Item[i]->Balance);
      out += add;
    }

    AllPtr->ClearAllAccounts();
    add.Format(L"Number of accounts: %ld.\n", AllPtr->Count);
    out += L"\n" + add;
    MessageBoxW(NULL, out, L"Result", MB_OK);

    //Raise an exception:
    AllPtr->RemoveAccount(1);
  }
  catch (const _com_error& e)
  {
    MessageBoxW(NULL, L"Oops! Index out of range!", L"Error", MB_OK);
  }
  CoUninitialize();// Uninitialize COM
  return 0;
}

      

        
        
        
      

    

Note: Item

is a vector in C ++. I have no idea how to change it to its normal functional form, i.e. Item(i)

instead of Item[i]

.

In VBA, you can use your favorite loop For Each

:

Sub CSharpBankTest()
 On Error GoTo Oops

  Dim Out As String
  Dim Bank As New BankServerCSharp.Bank            'New!

  Dim AllAccounts As BankServerCSharp.AllAccounts  'No New!
  Set AllAccounts = Bank.Accounts

  Dim AccountOne As BankServerCSharp.Account       'No New
  Set AccountOne = AllAccounts.AddAccount
  AccountOne.Deposit 47.11

  AllAccounts.AddAccount
  AllAccounts(2).Deposit 4711

  Dim i As Long
  Dim ac As BankServerCSharp.Account
  For Each ac In AllAccounts
    i = i + 1
    Out = Out & "Balance of account " & i & ": " & ac.Balance & vbNewLine
  Next
  Exit Sub
Oops:
  MsgBox "Error Message : " & Err.Description, vbOKOnly, "Error"
End Sub