Wrong number of arguments or invalid property assignment (VB6) when returning a C# tuple?

Question

I have a VB6 app and a C# Wrapper for a C object.

It works fine as built, however now I am trying to Return two values from the C# wrapper back to the VB6 app instead of the original one value being returned, and now I am getting the message - Wrong number of arguments or invalid property assignment.

I am guessing I just don't know how to correctly return multiple values. I have googled of course and applied a few ideas but still no go.

The working code looks like this.

VB6 app

Dim Result_ As BioxScan_Status

Result_ = ObjWinBio.OpenDevice

C# DLL

public BioxScan_Status OpenDevice()
{
.........

return BioxScan_Status.Connected ;
}


public enum BioxScan_Status
{
    Connected,
    Disconnected,
    Idle,
    Busy,
    Completed,
    Error,
    CaptureComplete
}

The above code works fine, the VB6 app calls the C# fucntion and gets the Return value of BioxScan_Status.Connected

However ...

What I am now trying to do is get Two values returned. One String value, One Int value, namely BioxScan_Status.Connected and also a UnitID

Here is what I have tried

C# DLL

public (string, string) OpenDevice()
{
.........

return (Convert.ToString(BioxScan_Status.Connected), Convert.ToString(_unitId));
}


public interface IWinbioWrap
{
    [DispId(1)]
    //BioxScan_Status OpenDevice(); // done
    (string, string) OpenDevice();

    ..........
 }

VB6 App

Dim Res()
Res = ObjWinBio.OpenDevice("", "")

On this line - Wrong number of arguments or invalid property assignment

Appreciate any thoughts.

Cheers

Answer 1

In VB6, you can't directly return a tuple. However, you can work by returning a custom class. Here's the modified C# code:

public class BioxScanResult
{
    public string Status { get; set; }
    public string UnitId { get; set; }
}

public BioxScanResult OpenDevice()
{
 ...

    var result = new BioxScanResult
    {
        Status = BioxScan_Status.Connected.ToString(),
        UnitId = _unitId.ToString()
    };

    return result;
}

Now, you can update your VB6 code to work with the BioxScanResult class:

Dim Res As Object
Set Res = ObjWinBio.OpenDevice()

Dim Status As String
Dim UnitId As String

Status = Res.Status
UnitId = Res.UnitId