Imports System.Runtime.InteropServices
Imports System.Threading

Public Class OleMessageFilter
    Implements IOleMessageFilter

    Public Shared Sub Register()
        Dim newFilter As IOleMessageFilter = New OleMessageFilter()
        Dim oldFilter As IOleMessageFilter = Nothing
        Dim iRetVal As Integer

        If (Thread.CurrentThread.GetApartmentState() = ApartmentState.STA) Then
            iRetVal = CoRegisterMessageFilter(newFilter, oldFilter)
        Else
            Throw New COMException("Unable to register message filter because the current thread apartment state is not STA.")
        End If

    End Sub

    Public Shared Sub Revoke()
        Dim oldFilter As IOleMessageFilter = Nothing
        CoRegisterMessageFilter(Nothing, oldFilter)
    End Sub

    Private Function HandleInComingCall(ByVal dwCallType As Integer, _
                                        ByVal hTaskCaller As System.IntPtr, _
                                        ByVal dwTickCount As Integer, _
                                        ByVal lpInterfaceInfo As System.IntPtr) _
                                        As Integer Implements IOleMessageFilter.HandleInComingCall

        Return SERVERCALL.SERVERCALL_ISHANDLED
    End Function

    Private Function RetryRejectedCall(ByVal hTaskCallee As System.IntPtr, _
                                       ByVal dwTickCount As Integer, _
                                       ByVal dwRejectType As Integer) _
                                       As Integer Implements IOleMessageFilter.RetryRejectedCall

        If dwRejectType = SERVERCALL.SERVERCALL_RETRYLATER Then
            Return 99
        End If

        Return -1
    End Function

    Private Function MessagePending(ByVal hTaskCallee As System.IntPtr, _
                                    ByVal dwTickCount As Integer, _
                                    ByVal dwPendingType As Integer) _
                                    As Integer Implements IOleMessageFilter.MessagePending

        Return PENDINGMSG.PENDINGMSG_WAITDEFPROCESS
    End Function

    <DllImport("Ole32.dll")> _
    Private Shared Function CoRegisterMessageFilter(ByVal newFilter As IOleMessageFilter, _
                                                    ByRef oldFilter As IOleMessageFilter) _
                                                    As Integer
    End Function
End Class

Enum SERVERCALL
    SERVERCALL_ISHANDLED = 0
    SERVERCALL_REJECTED = 1
    SERVERCALL_RETRYLATER = 2
End Enum

Enum PENDINGMSG
    PENDINGMSG_CANCELCALL = 0
    PENDINGMSG_WAITNOPROCESS = 1
    PENDINGMSG_WAITDEFPROCESS = 2
End Enum

<ComImport(), _
Guid("00000016-0000-0000-C000-000000000046"), _
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)> _
Interface IOleMessageFilter
    <PreserveSig()> _
    Function HandleInComingCall(ByVal dwCallType As Integer, _
                                ByVal hTaskCaller As IntPtr, _
                                ByVal dwTickCount As Integer, _
                                ByVal lpInterfaceInfo As IntPtr) _
                                As Integer

    <PreserveSig()> _
    Function RetryRejectedCall(ByVal hTaskCallee As IntPtr, _
                               ByVal dwTickCount As Integer, _
                               ByVal dwRejectType As Integer) _
                               As Integer

    <PreserveSig()> _
    Function MessagePending(ByVal hTaskCallee As IntPtr, _
                            ByVal dwTickCount As Integer, _
                            ByVal dwPendingType As Integer) _
                            As Integer
End Interface