Keydown

Imports System.Runtime.InteropServices
Imports System.Reflection
Imports System.Drawing
Imports System.Threading

Module Keyboard
  Public Declare Function UnhookWindowsHookEx Lib "user32" _
    (ByVal hHook As Integer) As Integer

  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

  Private Declare Function GetAsyncKeyState Lib "user32" _
    (ByVal vKey As Integer) As Integer

  Private Declare Function CallNextHookEx Lib "user32" _
    (ByVal hHook As Integer, _
    ByVal nCode As Integer, _
    ByVal wParam As Integer, _
    ByVal lParam As KBDLLHOOKSTRUCT) As Integer

  Public Structure KBDLLHOOKSTRUCT
    Public vkCode As Integer
    Public scanCode As Integer
    Public flags As Integer
    Public time As Integer
    Public dwExtraInfo As Integer
  End Structure

  ' Low-Level Keyboard Constants
  Private Const HC_ACTION As Integer      = 0
  Private Const LLKHF_EXTENDED As Integer = &H1
  Private Const LLKHF_INJECTED As Integer = &H10
  Private Const LLKHF_ALTDOWN As Integer  = &H20
  Private Const LLKHF_UP As Integer       = &H80

  ' Virtual Keys
  Public Const VK_TAB     = &H9
  Public Const VK_CONTROL = &H11
  Public Const VK_ESCAPE  = &H1B
  Public Const VK_DELETE  = &H2E

  Private Const WH_KEYBOARD_LL As Integer = 13&
  Public KeyboardHandle As Integer


  ' Implement this function to block as many
  ' key combinations as you'd like
  Public Function IsHooked( _
    ByRef Hookstruct As KBDLLHOOKSTRUCT) As Boolean

    Debug.WriteLine("Hookstruct.vkCode: " & Hookstruct.vkCode)
    Debug.WriteLine(Hookstruct.vkCode = VK_ESCAPE)
    Debug.WriteLine(Hookstruct.vkCode = VK_TAB)

    If (Hookstruct.vkCode = VK_ESCAPE) And _
      CBool(GetAsyncKeyState(VK_CONTROL) _
      And &H8000) Then

      Call HookedState("Ctrl + Esc blocked")
      Return True
    End If

    If (Hookstruct.vkCode = VK_TAB) And _
      CBool(Hookstruct.flags And _
      LLKHF_ALTDOWN) Then

      Call HookedState("Alt + Tab blockd")
      Return True
    End If

    If (Hookstruct.vkCode = VK_ESCAPE) And _
      CBool(Hookstruct.flags And _
        LLKHF_ALTDOWN) Then

      Call HookedState("Alt + Escape blocked")
      Return True
    End If

    Return False
  End Function

  Private Sub HookedState(ByVal Text As String)
    Debug.WriteLine(Text)
  End Sub

  Public Function KeyboardCallback(ByVal Code As Integer, _
    ByVal wParam As Integer, _
    ByRef lParam As KBDLLHOOKSTRUCT) As Integer

    If (Code = HC_ACTION) Then
      Debug.WriteLine("Calling IsHooked")

      If (IsHooked(lParam)) Then
        Return 1
      End If

    End If

    Return CallNextHookEx(KeyboardHandle, _
      Code, wParam, lParam)

  End Function


  Public Delegate Function KeyboardHookDelegate( _
    ByVal Code As Integer, _
    ByVal wParam As Integer, ByRef lParam As KBDLLHOOKSTRUCT) _
                 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")
    Else
      Debug.WriteLine("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