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Asked: 2026-06-02T22:13:59+00:00

I am using the following class found here to hook a keyboard combination globally

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I am using the following class found here to hook a keyboard combination globally in an app of mine.

Imports System.Runtime.InteropServices

Public Class KeyboardHook

<DllImport("User32.dll", CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall)> _
Private Overloads Shared Function SetWindowsHookEx(ByVal idHook As Integer, ByVal HookProc As KBDLLHookProc, ByVal hInstance As IntPtr, ByVal wParam As Integer) As Integer
End Function
<DllImport("User32.dll", CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall)> _
Private Overloads Shared Function CallNextHookEx(ByVal idHook As Integer, ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
End Function
<DllImport("User32.dll", CharSet:=CharSet.Auto, CallingConvention:=CallingConvention.StdCall)> _
Private Overloads Shared Function UnhookWindowsHookEx(ByVal idHook As Integer) As Boolean
End Function

<StructLayout(LayoutKind.Sequential)> _
Private Structure KBDLLHOOKSTRUCT
    Public vkCode As UInt32
    Public scanCode As UInt32
    Public flags As KBDLLHOOKSTRUCTFlags
    Public time As UInt32
    Public dwExtraInfo As UIntPtr
End Structure

<Flags()> _
Private Enum KBDLLHOOKSTRUCTFlags As UInt32
    LLKHF_EXTENDED = &H1
    LLKHF_INJECTED = &H10
    LLKHF_ALTDOWN = &H20
    LLKHF_UP = &H80
End Enum

Public Shared Event KeyDown(ByVal Key As Keys)
Public Shared Event KeyUp(ByVal Key As Keys)

Private Const WH_KEYBOARD_LL As Integer = 13
Private Const HC_ACTION As Integer = 0
Private Const WM_KEYDOWN = &H100
Private Const WM_KEYUP = &H101
Private Const WM_SYSKEYDOWN = &H104
Private Const WM_SYSKEYUP = &H105

Private Delegate Function KBDLLHookProc(ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer

Private KBDLLHookProcDelegate As KBDLLHookProc = New KBDLLHookProc(AddressOf KeyboardProc)
Private HHookID As IntPtr = IntPtr.Zero

Private Function KeyboardProc(ByVal nCode As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
    If (nCode = HC_ACTION) Then
        Dim struct As KBDLLHOOKSTRUCT
        Select Case wParam
            Case WM_KEYDOWN, WM_SYSKEYDOWN
                RaiseEvent KeyDown(CType(CType(Marshal.PtrToStructure(lParam, struct.GetType()), KBDLLHOOKSTRUCT).vkCode, Keys))
            Case WM_KEYUP, WM_SYSKEYUP
                RaiseEvent KeyUp(CType(CType(Marshal.PtrToStructure(lParam, struct.GetType()), KBDLLHOOKSTRUCT).vkCode, Keys))
        End Select
    End If
    Return CallNextHookEx(IntPtr.Zero, nCode, wParam, lParam)
End Function

Public Sub New()
    HHookID = SetWindowsHookEx(WH_KEYBOARD_LL, KBDLLHookProcDelegate, System.Runtime.InteropServices.Marshal.GetHINSTANCE(System.Reflection.Assembly.GetExecutingAssembly.GetModules()(0)).ToInt32, 0)
    If HHookID = IntPtr.Zero Then
        Throw New Exception("Could not set keyboard hook")
    End If
End Sub

Protected Overrides Sub Finalize()
    If Not HHookID = IntPtr.Zero Then
        UnhookWindowsHookEx(HHookID)
    End If
    MyBase.Finalize()
End Sub

End Class

It works nice even if the app has focus or not but i have a problem. My application is using 

 My.Computer.Network.UploadFile

During the upload the kayboard strokes stop responding. Mouse is ok.

How can i keep keyboard alive during other operations inside my application?

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1 Answer

  1. Editorial Team

    Yes, that’s asking for trouble. Windows can only call your hook callback method when your program is pumping the message loop. There is no other mechanism available to Windows to make a call on your main thread without causing drastic re-entrancy problems.

    That stops working well when your main thread goes off doing something else, like uploading a file. This is a general requirement for GUI apps, occupying the main UI thread with other tasks makes the user interface catatonic. It stops responding to input and stops painting. After a couple of seconds, the Windows window manager steps in and replaces your main window with the ‘ghost window’, with “Not Responding” in the title bar. You get your nose rubbed into it harder because this now also stops any keyboard input from getting processed, Window can’t call the hook callback.

    You need to perform long running tasks on another thread so the UI thread can remain responsive. Or in the specific case you are talking about, use UploadFileAsync() instead.

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