Passing string array from VB6 to C#.net

Question

How to pass a VB6 string array [Assume, s =Array("a", "b", "c", "d")] to C#.Net through COM Interop?

I tried to implement passing C# string array to VB and VB string array to C# as below C#->VB working fine but other way (VB=>C#) giving a compile error called "Function or interface marked as restricted, or the function uses an automation type not supported in visual basic" . My code below

C#

    public interface ITest   
    { 
         string[] GetArray();
         void SetArray(string[] arrayVal );
    }

    public class Test : ITest 
    {
        string[] ITest.GetArray() {                                //Working fine
            string[] stringArray = { "red ", "yellow", "blue" };
            return stringArray;
        }
    }

    void ITest.SetArray(string[] arrayVal) //Giving an issue
    {
       string[] stringArray1 = arrayVal;
    }

VB

 Dim str As Variant
    Debug.Print ".NET server returned: "    
    For Each str In dotNETServer.GetArray      'dotNETServer=TestServer.Test
            Debug.Print str
    Next

    Dim arr(3) As String
    arr(1) = "Pahee"
    arr(2) = "Tharani"
    arr(3) = "Rathan"

    dotNETServer.SetArray (arr)         'This one causing the compile error which I mentioned earlier

Update: ::::::

We need to pass the array as reference in C#. Change it in the interface and method

void SetArray(ref string[] arrayVal ); //ref added

Answer 1

Marshaling to appropriate type will solve your problem. Note marshaling and ref keyword change below

void ITest.SetArray([MarshalAs(UnmanagedType.SafeArray, SafeArraySubType=VT_BSTR)] ref string[] arrayVal)
{
   string[] stringArray1 = arrayVal;
}

I made this solution based on your code and issue that you are not able to fetch data from VB6. If above solution does not work for you the do try finding the array type/subtype suitable for your application here http://msdn.microsoft.com/en-us/library/z6cfh6e6(v=vs.110).aspx

Answer 2

Your issue was in the Vb6 code:

dotNETServer.SetArray (arr)

This is actually forcing arr to be passed by value because it is enclosed by parentheses with no Call keyword.

You want to do this:

Call dotNETServer.SetArray(arr)

or

dotNETServer.SetArray arr