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

Mon, 06 Aug 2007 07:24:37 Z

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

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

Mon, 06 Aug 2007 15:09:29 Z

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

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

Wed, 08 Aug 2007 11:44:49 Z

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

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

Tue, 16 Oct 2007 13:51:17 Z

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...

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

Tue, 16 Oct 2007 14:40:16 Z

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...

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

Tue, 16 Oct 2007 15:08:15 Z

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.

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

Tue, 16 Oct 2007 15:43:57 Z

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.

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

Tue, 16 Oct 2007 16:54:48 Z

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.

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

Fri, 29 Aug 2008 21:44:13 Z

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 !