keyboard hooking reporting twice!

[death_entry]

I found some code which shows the keys that have been hooked. I have simplified the code alot from the example, but it seems to report the hooked keys twice and I need this only to happen once. I am have been looking at it for sometime but I can't see what is making it report the hook twice and not once.

The best way to see this happening is by pressing a key and the output message will be displayed twice.

I thought perhaps its reporting the keydown and keyup events maybe not sure whats going on.

Also can anyone explain to me why WH_KEYBOARD_LL has to = 13? How do you know it's 13 and not some other number, can't seem to find a referance to this anywhere.

Imports System.Runtime.InteropServices
Imports System.Reflection
Imports System.Drawing
Imports System.Threading
 
Module Keyboard
 
    Public Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" (ByVal idHook As Integer, ByVal lpfn As KeyboardHookDelegate, ByVal hmod As Integer, ByVal dwThreadId As Integer) As Integer
    Public Declare Function UnhookWindowsHookEx Lib "user32" (ByVal hHook As Integer) As Integer
    Declare Function keybd_event Lib "user32" Alias "keybd_event" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long) As Long
 
    Public Structure keyboardStructure
        Public vkCode As Integer
        Public scanCode As Integer
        Public flags As Integer
        Public time As Integer
        Public dwExtraInfo As Integer
    End Structure
 
 
 
 
 
    Private Const WH_KEYBOARD_LL As Integer = 13&
    Public KeyboardHandle As Integer
 
 
    Public Sub checkKeys(ByRef Hookstruct As keyboardStructure)
 
        Debug.WriteLine("Hookstruct.vkCode: " & Hookstruct.vkCode)
 
        If (Hookstruct.vkCode = 49) Then
            keybd_event(50, 0, 0, 0)
        End If
 
    End Sub
 
 
    Private Sub hookOutput(ByVal Text As String)
        Debug.WriteLine(Text)
 
    End Sub
 
 
    Public Function keyboardCallback(ByVal Code As Integer, ByVal wParam As Integer, ByRef lParam As keyboardStructure) As Integer
        checkKeys(lParam)
    End Function
 
 
    Public Delegate Function KeyboardHookDelegate(ByVal Code As Integer, ByVal wParam As Integer, ByRef lParam As keyboardStructure) As Integer
 
    <MarshalAs(UnmanagedType.FunctionPtr)> Private callback As KeyboardHookDelegate
 
    Public Sub HookKeyboard()
        callback = New KeyboardHookDelegate(AddressOf keyboardCallback)
 
        KeyboardHandle = SetWindowsHookEx(WH_KEYBOARD_LL, callback, Marshal.GetHINSTANCE([Assembly].GetExecutingAssembly.GetModules()(0)).ToInt32, 0)
 
        Call CheckHooked()
    End Sub
 
    Public Sub CheckHooked()
        If (Hooked()) Then
            '' Debug.WriteLine("Keyboard hooked")
            MessageBox.Show("Keyboard hooked")
        Else
            ''Debug.WriteLine("Keyboard hook failed: " & Err.LastDllError)
            MessageBox.Show("Keyboard hook failed: " & Err.LastDllError)
        End If
    End Sub
 
    Private Function Hooked()
        Hooked = KeyboardHandle <> 0
    End Function
 
    Public Sub UnhookKeyboard()
        If (Hooked()) Then
            Call UnhookWindowsHookEx(KeyboardHandle)
        End If
    End Sub
 
End Module