How do you disable the alt key?????

Question

Hi, i'm new at this, how would you stop someone using the alt key, like alt+F4, alt+ctrl+delete OR alt+tab

Answer 1

I'll tell you, but only if you PROMISE you aren't going to write an app which is so so self-important that it thinks it must be always on top

Answer 2

Hi,

 

I hope that this will get you started; watch for word wrap:

 

Code Snippet

Imports System.Runtime.InteropServices

Imports System.Reflection

Module mKeyboard

#Region "Declarations"

    Private Const HC_ACTION As Integer = 0

    Private Const WH_KEYBOARD_LL As Integer = 13&

 

    Private Structure KBDLLHookStruct

        Public vkCode As Integer

        Public scanCode As Integer

        Public flags As Integer

        Public time As Integer

        Public dwExtraInfo As Integer

    End Structure

 

    <MarshalAs(UnmanagedType.FunctionPtr)> _

    Private callback As KeyboardHookDelegate

    Private mbBlockKeys As Boolean = True

    Private miKeyboardHandle As Integer = 0

 

    Private Delegate Function KeyboardHookDelegate(ByVal Code As Integer, _

        ByVal wParam As Integer, ByRef lParam As KBDLLHookStruct) 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

 

    Private 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 UnhookWindowsHookEx Lib "user32" ( _

        ByVal hHook As Integer) As Integer

#End Region

 

#Region "Properties"

    Public Property BlockKeyCombinations() As Boolean

        Get

            Return mbBlockKeys

        End Get

        Set(ByVal value As Boolean)

            mbBlockKeys = value

        End Set

    End Property

 

    Public ReadOnly Property IsHooked() As Boolean

        Get

            Return miKeyboardHandle <> 0

        End Get

    End Property

#End Region

 

    Public Function IsInIDE() As Boolean

        Return System.Diagnostics.Debugger.IsAttached

    End Function

 

    Public Sub HookKeyboard()

        ' Release any existing keyboard hook.

        UnhookKeyboard()

 

        If Not IsInIDE() Then

            callback = New KeyboardHookDelegate(AddressOf KeyboardCallback)

            miKeyboardHandle = SetWindowsHookEx(WH_KEYBOARD_LL, callback, _

            Marshal.GetHINSTANCE([Assembly].GetExecutingAssembly.GetModules()(0)).ToInt32, 0)

        End If

    End Sub

 

    Public Sub UnhookKeyboard()

        If (IsHooked()) Then Call UnhookWindowsHookEx(miKeyboardHandle)

    End Sub

 

    Private Function BlockKeyCombination( _

        ByVal Hookstruct As KBDLLHookStruct) As Boolean

 

        Dim bResult As Boolean = False

 

        If mbBlockKeys Then

            Select Case Hookstruct.vkCode

                Case System.ConsoleKey.Escape

                    If My.Computer.Keyboard.CtrlKeyDown Then

                        Debug.Print("Blocking: Ctrl-Esc")

                        bResult = True

                    ElseIf My.Computer.Keyboard.AltKeyDown Then

                        Debug.Print("Blocking: Alt-Esc")

                        bResult = True

                    End If

                Case System.ConsoleKey.Tab

                    If My.Computer.Keyboard.AltKeyDown Then

                        Debug.Print("Blocking: Alt-Tab")

                        bResult = True

                    End If

                Case System.ConsoleKey.RightWindows, System.ConsoleKey.LeftWindows

                    Debug.Print("Blocking: Windows Key")

                    bResult = True

                Case System.ConsoleKey.Applications

                    Debug.Print("Blocking: Application Key")

                    bResult = True

                Case System.ConsoleKey.F4

                    If My.Computer.Keyboard.AltKeyDown Then

                        Debug.Print("Blocking: Alt-F4")

                        bResult = True

                    End If

                Case Else

            End Select

        End If

 

        Return bResult

    End Function

 

    Private Function KeyboardCallback(ByVal Code As Integer, _

        ByVal wParam As Integer, ByRef lParam As KBDLLHookStruct) As Integer

 

        Dim lResult As Integer = 0

        If (Code = HC_ACTION) AndAlso (BlockKeyCombination(lParam)) Then

            lResult = 1

        Else

            lResult = CallNextHookEx(miKeyboardHandle, Code, wParam, lParam)

        End If

 

        Return lResult

    End Function

End Module

 

 

Answer 3

James,

 

I am having a very similar issue to Simone1.  I will try this out and see if it addresses the problem.

 

Thank you for the help...

 

Answer 4

James,

 

I got the code into my program, but what do I do with it?  What do I call/pass so that input is checked?

 

I have it as a module available to the whole program.  I can call the HookKeyboard public sub - but when I debug the code, pressing the keys that your code should trap, nothing happens...

 

Answer 5

Hi,

Call mKeyboard.HookKeyboard in the application startup. 

Call mKeyboard.UnhookKeyboard when shutting down.

Change mKeyboard.BlockKeyCombination to disallow key combinations.

Set mKeyboard.BlockKeyCombinations to True to block the defined key combinations.

 

That should get you going.  Keep in mind that HookKeyboard will not install a new keyboard hook when running in Debug mode.  Try running in release mode.

 

If you are still stuck, please let me know.

Answer 6

kandaras0 wrote:

Hi, i'm new at this, how would you stop someone using the alt key, like alt+F4, alt+ctrl+delete OR alt+tab

 

You can perhaps aslo use the SystemParametersInfo API here.  This API will block all these keys ( except for Alt + Ctrl + Del ).  The reaon for this is that whether or not you specify it, the Task manager ( on Windows XP ) will still show.

That will be your biggest headache.

You can disable the Taskmanager by adding a Timer to your Form, and keep bringing your form to the fron ( ok, it won't disable tha taskmanager, but it will hide it )

To really disable the Taskmanager from showing by editing the registry key :

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\LogonType

 

or you could get the Taskmanager's Process Id with the GetWindowThreadProcessId API, then terminate it with the TerminateProcess API.

 

To be honest.  I'm not if any of my comments were illegal in this forum, so mods, feel free to edit / delet as you see fit.

 

Another comment kandaras, is that it is very impractical and illogical  why anyone would need to hide the taskmanager completely.  The Task Manager exists for a reason.

Answer 7

HanneSThEGreaT wrote:

Another comment kandaras, is that it is very impractical and illogical  why anyone would need to hide the taskmanager completely.  The Task Manager exists for a reason.

 

I agree that most applications should not prevent Task Manager from popping up nor should they block key combinations.  Instead, policies are probably a better way to go.  In my particular case, the applications I write control machinery.  Forcibly killing the application or doing other tasks in Windows could cause machine malfunctions.  Since we do not always have have access to change policies, it was easier/quicker to disable "stuff" within the application.  That being said, we do allow that ability to be configured by user access (operators can't exit the app, but admins can for example).

 

I am, however, always open to different solutions.

Answer 8

Hello James,


I had to change the visibility of BlockKeyCombination to Public because i couldn't call it from my window.

Also, when i call the BlockKeyCombination function, no parameters pulls out thru IntelliSense.

What should i specify in the KBDLLHookStruct structure ?


I have seen this :

KBDLLHOOKSTRUCT Structure

http://msdn.microsoft.com/en-us/library/ms644967(VS.85).aspx

But it doesn't tell what values are for the desired key ... etc


Help please,

Thank you !