COM visible List from C# to vb6

Question

I have ClassLibrary (in visual studio 2010 C#) with a class Car:

[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Car")]
public class Car
{
    public Car()
    {
        Name = "";
        Parts = new List<string>();
    }

    public string Name { get; set; }

    public List<string> Parts { get; set; }
}

But when I use it in vb6 project: there is no property "Parts": https://i.sstatic.net/nMfEi.jpg

What can I do to make property List<> visible?

Of course, the file "AssemblyInfo.cs" contains:

[assembly: ComVisible(true)]

P.S. I really do not want to create for each List the class, like this:

public class Parts
{
    private List<string> _parts;

    public Parts()
    {
        _parts = new List<string>();
    }

    public void Add(string part)
    {
        _parts.Add(part);
    }

    public string GetAt(int index)
    {
        if (0 <= index && index < _parts.Count)
            return _parts[index];
        return "";
    }

    public void Clear()
    {
        _parts.Clear();
    }

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

because there are too many.

D Stanley · Accepted Answer · 2014-06-19 14:20:38Z

3

COM does not support generic collections; you'll have to use an array or ArrayList instead:

[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Car")]
public class Car
{
    public Car()
    {
        Name = "";
        Parts = new string[];
    }

    public string Name { get; set; }

    public string[] Parts { get; set; }
}

If you want to use a List behind-the-scenes you could use a List<string> as a backing variable, then change the property accessors to translate the list to/from an array:

[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Car")]
public class Car
{

    private List<string> _Parts;

    public Car()
    {
        Name = "";
        _Parts = new List<string>();
    }

    public string Name { get; set; }

    public string[] Parts 
    { 
        get
        {
            return _Parts.ToArray();
        } 
        set
        {
            _Parts = new List<string>(value);
        } 
    }
}

answered Jun 19, 2014 at 14:20

D Stanley

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3 Comments

Jon Egerton Over a year ago

Out of interest, if you just inherit from the generic to make a concrete definition (ie class Parts : List<Part>) and add the attributes, would that be acceptable for Com Visibility?

zhigarartem Over a year ago

I added class:

[ClassInterface(ClassInterfaceType.AutoDual)]     [ProgId("Modem_TAO_Well3DView.Parts")]     public class Parts : List<string>     {         public Parts()         {             MaxCount = 50;         }          public static int MAX_COUNT = 50;          public int GetMaxCount()         {             return 50;         }          public int MaxCount { get; set; }     }

But nothing is visible (properties, fields, etc). Perhaps you meant IList<Part>

zhigarartem Over a year ago

I hope - there is a class attribute that allows access to the property List

zhigarartem · Accepted Answer · 2014-06-20 10:11:39Z

I did not want to do so, but had:

[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Car")]
public class Car
{
    public Car()
    {
        Name = "";
        Parts = new Parts();
    }

    public string Name { get; set; }

    public Parts Parts { get; set; }
}

[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Parts")]
public class Parts : IList<string>
{
    private List<string> _parts;

    public Parts()
    {
        _parts = new List<string>();
    }

    #region IList<string> Members

    public int IndexOf(string item)
    {
        return _parts.IndexOf(item);
    }

    public void Insert(int index, string item)
    {
        _parts.Insert(index, item);
    }

    public void RemoveAt(int index)
    {
        _parts.RemoveAt(index);
    }

    public string this[int index]
    {
        get
        {
            return _parts[index];
        }
        set
        {
            _parts[index] = value;
        }
    }

    #endregion

    #region ICollection<string> Members

    public void Add(string item)
    {
        _parts.Add(item);
    }

    public void Clear()
    {
        _parts.Clear();
    }

    public bool Contains(string item)
    {
        return _parts.Contains(item);
    }

    public void CopyTo(string[] array, int arrayIndex)
    {
        _parts.CopyTo(array, arrayIndex);
    }

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

    public bool Remove(string item)
    {
        return _parts.Remove(item);
    }

    #endregion

    #region ICollection<string> Members


    public bool IsReadOnly
    {
        get { throw new NotImplementedException(); }
    }

    #endregion

    #region IEnumerable<string> Members

    public IEnumerator<string> GetEnumerator()
    {
        throw new NotImplementedException();
    }

    #endregion

    #region IEnumerable Members

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }

    #endregion
}

In vb6:

Option Explicit
Dim car As New ClassLibrary1.car
Dim parts As New ClassLibrary1.parts

Private Sub Form_Load()

    parts.Add "wheel"
    parts.Add "door"
    parts.Add "hood"
    parts.Add "trunk"

    car.Name = "GAS-24"
    Set car.parts = parts
    car.parts.RemoveAt (0)
End Sub

Drawback of this approach is a lot of code:(

Let me know, if anyone knows something like this:

//**[MakeVisibleListInVB6]**
[ClassInterface(ClassInterfaceType.AutoDual)]
[ProgId("ClassLibrary1.Car")]
public class Car
{
    public Car()
    {
        Name = "";
        Parts = new Parts();
    }

    public string Name { get; set; }

    public List<string> Parts { get; set; }
}

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