I wanted to call the GetIdsOfNames function from a COM object that implements the IDispatch interface in c#. I've written the following code but it fails with the DISP_E_UNKNOWNNAME. Is this the correct approach to do this?
Object so = Activator.CreateInstance(Type.GetTypeFromProgID("ProgID"));
Object[] args = new Object[5];
string[] rgsNames = new string[1];
rgsNames[0] = "PrintNormal";
uint LOCALE_SYSTEM_DEFAULT = 0x0800;
uint lcid = LOCALE_SYSTEM_DEFAULT;
int cNames = 1;
int[] rgDispId = new int[1];
args[0] = IntPtr.Zero;
args[1] = rgsNames;
args[2] = cNames;
args[3] = lcid;
args[4] = rgDispId;
Object result = so.GetType().InvokeMember("GetIDsOfNames", BindingFlags.InvokeMethod, null, so, args);
Thanks,
Richard
Yes, doesn't work, the RCW doesn't expose the IDispatch methods. You have to obtain the IDispatch interface reference explicitly. This worked well:
using System;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
class Program {
static void Main() {
Object so = Activator.CreateInstance(Type.GetTypeFromProgID("SAPI.SpVoice"));
string[] rgsNames = new string[1];
int[] rgDispId = new int[1];
rgsNames[0] = "Speak";
IDispatch disp = (IDispatch)so;
Guid dummy = Guid.Empty;
disp.GetIDsOfNames(ref dummy, rgsNames, 1, 0x800, rgDispId);
Console.WriteLine(rgDispId[0]);
}
[ComImport, InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("00020400-0000-0000-C000-000000000046")]
private interface IDispatch {
int GetTypeInfoCount();
[return: MarshalAs(UnmanagedType.Interface)]
ITypeInfo GetTypeInfo([In, MarshalAs(UnmanagedType.U4)] int iTInfo, [In, MarshalAs(UnmanagedType.U4)] int lcid);
void GetIDsOfNames([In] ref Guid riid, [In, MarshalAs(UnmanagedType.LPArray)] string[] rgszNames, [In, MarshalAs(UnmanagedType.U4)] int cNames, [In, MarshalAs(UnmanagedType.U4)] int lcid, [Out, MarshalAs(UnmanagedType.LPArray)] int[] rgDispId);
}
}
No you cannot, because InvokeMember internally uses GetIDsOfNames, and this one only checks actual methods, not the first 6 in IDispatch. Or in other words, GetIDsOfNames cannot be invoked using IDispatch's method Invoke. That is how COM works.
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