C# Signature:

[DllImport("oleaut32.dll", SetLastError=false, ExactSpelling=true)]
static extern int VarBstrFromDisp(IntPtr Disp, int lcid, int dwFlags, [MarshalAs(UnmanagedType.BStr)] out string pbstrOut);

VB Signature:

Declare Function VarBstrFromDisp Lib "oleaut32.dll" (Byval Disp as IntPtr, Byval lcid As Integer, Byref pbstrOut as String) As Integer

User-Defined Types:

None.

Alternative Managed API:

There is no alternative API in .NET except for Dispatch Invoke the default value (DispId == 0)

However, you could use the dynamic keyword. But this expects you to know the name of the default property. (Which can be Value but Text or any name as the original Dispatch interface developer (eg in VB6) had intended to).

Notes:

The sample cannot be used on DCOM (remote COM). It is not tested.

Tips & Tricks:

Please add some!

Sample Code:

object pComObject = rs.Fields[0]; // ADODB COM stuff

if (Marshal.IsComObject(pComObject)) // shows as System.__ComObject

{

   string pbstrOut;
   int hr = VarBstrFromDisp(Marshal.GetIDispatchForObjectInContext(pComObject), Thread.CurrentThread.CurrentCulture.LCID, 0, out pbstrOut);
   if (hr != 0)
   {
       Marshal.ThrowExceptionForHR(hr);
   }
}