I have searched the web tirelessly and tried every possible solution I have come across; yet cannot find a working solution.

I have a mouse hook that I have been using for a long time now and it works great except for when I try to distinguish forward/back mouse wheel messages.

I have seen the mouseData member of the MSLLHOOKSTRUCT structure declared as an Integer and UInteger. Either way I declare it, I am unable to get the HIWORD for the WM_MOUSEWHEEL message to distinguish forwards from back because the value is always the same when I wheel forward or back.

Test Output:

Wheel Forward:

mouseData: 23074474
HIWORD: 352

Wheel Back:

mouseData: 23074474
HIWORD: 352

Code:

    <Extension>
    Public Function HIWORD(value As Integer) As Integer
        Return BitConverter.ToInt16(BitConverter.GetBytes(value), 2)
    End Function

    Private Shared MouseHookProcedure As HookProcHandler
    Private Shared PreviousCallback As Object()
    Private Shared ProcPtrSet As Boolean
    Private Shared HookHandle As IntPtr

    Public Shared Function Start() As Boolean
        If HookHandle <> IntPtr.Zero Then Return True
        If Not ProcPtrSet Then
            ProcPtrSet = True
            MouseHookProcedure = New HookProcHandler(AddressOf HookProc)
        End If
        Using p As Process = Process.GetCurrentProcess()
            Using m As ProcessModule = p.MainModule
                SetWindowsHookEx(HOOKTYPE.WH_MOUSE, MouseHookProcedure, Pinvoke.Kernel32.Functions.GetModuleHandle(m.ModuleName), Pinvoke.Kernel32.Functions.GetCurrentThreadId)
            End Using
        End Using
        If HookHandle = 0 Then Return False Else Return True
    End Function

    Public Shared Function [Stop]() As Boolean
        Return UnhookWindowsHookEx(HookHandle)
    End Function

    Private Shared Function HookProc(nCode As Integer, wParam As IntPtr, lParam As IntPtr) As Integer
        Dim MSLLHS As MSLLHOOKSTRUCT = Marshal.PtrToStructure(lParam, GetType(MSLLHOOKSTRUCT))
        If nCode < 0 Then
            Return CallNextHookEx(HookHandle, nCode, wParam, lParam)
        Else
            ' Catch duplicate messages caused by the default behavior of the MouseProc function.
            Dim Msg As MouseMessages = CType(wParam, MouseMessages)
            If PreviousCallback IsNot Nothing Then
                If CType(PreviousCallback(0), MouseMessages) = Msg AndAlso CompairMSLLHOOKSRUCT(PreviousCallback(1), MSLLHS) AndAlso CType(PreviousCallback(2), Date) = Now Then
                    GoTo NextCallback
                End If
            End If
            ' Raise Event
            Select Case Msg
                Case MouseMessages.MouseWheel
                    Msg = If(CType(MSLLHS.mouseData, Integer).HIWORD > 0, MouseMessages.MouseWheelForward, MouseMessages.MouseWheelBack)
                    RaiseEvent Message(Msg MSLLHS)
                Case Else
                    RaiseEvent Message(Msg, MSLLHS)
            End Select
            PreviousCallback = New Object(2) {CType(wParam, MouseMessages), MSLLHS, Now}
NextCallback:
            Try
                Return CallNextHookEx(HookHandle, nCode, wParam, lParam)
            Catch ex As Exception
                Return [Stop]()
            End Try
        End If
    End Function

    Private Shared Function CompairMSLLHOOKSRUCT(left As MSLLHOOKSTRUCT, right As MSLLHOOKSTRUCT) As Boolean
        Return left.pt.X = right.pt.X AndAlso left.pt.Y = right.pt.Y AndAlso left.mouseData = right.mouseData AndAlso left.flags = right.flags AndAlso left.time = right.time AndAlso left.dwExtraInfo = right.dwExtraInfo
    End Function

Pinvoke:

Public Delegate Function HookProcHandler(nCode As Integer, wParam As IntPtr, lParam As IntPtr) As Integer

<DllImport(User32, CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall, SetLastError:=True)>
Public Shared Function UnhookWindowsHookEx(idHook As IntPtr) As Boolean
End Function

<DllImport(User32, CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall, SetLastError:=True)>
Public Shared Function SetWindowsHookEx(idHook As Integer, lpfn As HookProcHandler, hInstance As IntPtr, threadId As Integer) As IntPtr
End Function

<DllImport(User32, CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall, SetLastError:=True)>
Public Shared Function CallNextHookEx(hhk As IntPtr, nCode As Integer, wParam As IntPtr, lParam As IntPtr) As IntPtr
End Function

<DllImport(Kernel32, CharSet:=CharSet.Auto, SetLastError:=True)>
Public Shared Function GetModuleHandle(lpModuleName As String) As IntPtr
End Function

<StructLayout(LayoutKind.Sequential)>
Public Structure MSLLHOOKSTRUCT    
    Public pt As POINT
    Public mouseData As UInteger
    Public flags As UInteger
    Public time As UInteger
    Public dwExtraInfo As IntPtr
End Structure

<StructLayout(LayoutKind.Sequential)>
Public Structure POINT
    Public X As Integer
    Public Y As Integer
    Public Sub New(ByVal X As Integer, ByVal Y As Integer)
        Me.X = X
        Me.Y = Y
    End Sub
End Structure

Public Enum MouseMessages As UInteger
    MouseWheel = WindowsMessages.WM_MOUSEWHEEL ' &H20E
    ' Etc...
End Enum