MessageFilter.cs

// Taken from https://download.beckhoff.com/download/Document/automation/twincat3/AutomationInterface_pdf_EN.pdf
namespace EnvDteUtils
{
    using System;
    using System.Runtime.InteropServices;
    public class MessageFilter : IOleMessageFilter
    {
        public static void Register()
        {
            IOleMessageFilter newFilter = new MessageFilter();
            IOleMessageFilter oldFilter = null;
            CoRegisterMessageFilter(newFilter, out oldFilter);
        }
        public static void Revoke()
        {
            IOleMessageFilter oldFilter = null;
            CoRegisterMessageFilter(null, out oldFilter);
        }
        int IOleMessageFilter.HandleInComingCall(int dwCallType, System.IntPtr hTaskCaller, int dwTickCount,
        System.IntPtr lpInterfaceInfo)
        {
            return 0;
        }
        int IOleMessageFilter.RetryRejectedCall(System.IntPtr hTaskCallee, int dwTickCount, int
        dwRejectType)
        {
            if (dwRejectType == 2)
            {
                return 99;
            }
            return -1;
        }
        int IOleMessageFilter.MessagePending(System.IntPtr hTaskCallee, int dwTickCount, int dwPendingType)
        {
            return 2;
        }
        [DllImport("Ole32.dll")]
        private static extern int CoRegisterMessageFilter(IOleMessageFilter newFilter, out IOleMessageFilter
        oldFilter);
    }

    [ComImport(), Guid("00000016-0000-0000-C000-000000000046"),
    InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
    interface IOleMessageFilter
    {
        [PreserveSig]
        int HandleInComingCall(int dwCallType, IntPtr hTaskCaller, int dwTickCount, IntPtr lpInterfaceInfo);
        [PreserveSig]
        int RetryRejectedCall(IntPtr hTaskCallee, int dwTickCount, int dwRejectType);
        [PreserveSig]
        int MessagePending(IntPtr hTaskCallee, int dwTickCount, int dwPendingType);
    }
}