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MCL Global Hotkey ActiveX control

, 12 May 2003 CPOL 67.7K 1.1K 18
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A system wide hotkey control written in VB6


The attached source code is for a system-wide global hotkey control written in Visual Basic 6, originally posted on the Merrion Computing Downloads.

Registering a hotkey

There are two API calls concerned with registering a system wide hotkey: RegisterHotkey and UnregisterHotkey - the declarations are:

To register the hotkey, you need to specify hwnd - the window which will be notified when the hotkey combination is pressed, id - the unique identifier for the hotkey, fsModifiers - the modifiers of the hotkey (i.e. whether ALT, SHIFT, CTRL or WIN keys are pressed) and finally vKey - the virtual key code for the hot key. The modifiers which can be combined together are:

Listening Out for the hotkey

When a hotkey which has been registered successfully is pressed, the window specified in the hwnd is posted a WM_HOTKEY registered window message. Additionally the lParam parameter holds the modifier and virtual key code in its high and low words respectively.

Visual Basic does not handle the WM_HOTKEY message by default which means that you need to subclass the window hwnd in order to respond to it. To do this, you use the API call SetWindowLong with the index GWL_WNDPROC to replace the existing window procedure with yours.

Using the Control in your Application

To use this control in a Visual Basic application, compile the attached source code and then add an instance of the resulting OCX to your project. Add an instance of the MCLHotkey control to your form and press F4 to set the properties. Then add the code that you want executed when the hotkey is pressed to the HotkeyPressed event:

Private Sub MCLHotkey1_HotkeyPressed()
  Debug.Print "You pressed the hotkey at " & Now
End Sub
'\\ API Calls used in subclassing windows....
Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" _
	(ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal msg As Long, _
	ByVal wParam As Long, ByVal lParam As Long) As Long
Private Declare Function DefWindowProc Lib "user32" Alias "DefWindowProcA" _
	(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
	ByVal lParam As Long) As Long
'\\ Window specific information
Private Declare Function GetWindowLongApi Lib "user32" Alias "GetWindowLongA" _
	(ByVal hwnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLongApi Lib "user32" Alias "SetWindowLongA" _
	(ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Const GWL_WNDPROC = (-4)
Public Function VB_WindowProc(ByVal hwnd As Long, ByVal wMsg As Long, _
	ByVal wParam As Long, ByVal lParam As Long) As Long

Dim VKey As Long
Dim Modifier As Long

If wMsg = WM_HOTKEY Then
    VKey = HiWord(lParam)
    Modifier = LoWord(lParam)
    '\\ Raise an event here to respond to the hotkey
End If

If sWindow.OldWndProc = 0 Then
    VB_WindowProc = DefWindowProc(hwnd, wMsg, wParam, lParam)
    VB_WindowProc = CallWindowProc(sWindow.OldWndProc, hwnd, wMsg, wParam, lParam)
End If

End Function
Public Enum enHotkeyModifiers
    MOD_ALT = &H1
    MOD_SHIFT = &H4
    MOD_WIN = &H8
End Enum
Private Declare Function RegisterHotKey Lib "user32" (ByVal hwnd As Long, _
    ByVal id As Long, ByVal fsModifiers As Long, ByVal vk As Long) As Long
Private Declare Function UnregisterHotKey Lib "user32" (ByVal hwnd As Long, _
    ByVal id As Long) As Long


  • 12th May, 2003: Initial post


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Duncan Edwards Jones
Software Developer (Senior)
Ireland Ireland
C# / SQL Server developer
Microsoft MVP 2006, 2007
Visual Basic .NET

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Comments and Discussions

Generalmisbehave on window vista Pin
arunkumar.1658330-Jan-09 22:19
memberarunkumar.1658330-Jan-09 22:19 
Generalthis is great but Pin
Leerz5-Dec-06 6:16
memberLeerz5-Dec-06 6:16 
GeneralRe: this is great but Pin
Duncan Edwards Jones8-Feb-07 3:51
memberDuncan Edwards Jones8-Feb-07 3:51 
GeneralExcellent Control but a couple of problems Pin
AvoSoftwareTeam29-Oct-05 2:38
memberAvoSoftwareTeam29-Oct-05 2:38 
I found this control to be very good, however there where a couple of problems that meant I had to edit the original code.

The problems all arise if you wish to use more than one Global Hotkey.

1) If you try and use a second Hotkey it Unregisters the previous.

This is caused because the Atom is a shared variable and it is decremented and then incremented when you register a new Hotkey. This results in each control using the same Atom.

To resolve this I created a new member Variable in SystemWideHotkeyComponent

Private _MyAtom As Int32 = 0

and when I setup the Hotkey the new atom is asigned to this member variable. I also check whether it was previously assigned so only one atom is assigned per control.

from StartHotkeyWatch:

If _MyAtom = 0 Then
mhAtom += 1
_MyAtom = mhAtom
End If

This code ensures that a unique Atom is assigned once per control.

2) The event handlers for each control receive all Hotkey presses.

This is because the event is fired for any Hotkey press and not the individual hotkey relatting to the control. I had to change the Message handler in GlobalHotkeyListener to check whether the correct hotkey had been pressed. Only if the hotkey in LParam matches the listening hotkey does it fire the event.

Add this member variable:
Private _KeyMask As Integer

Add this to New()
_KeyMask = vkey << 16 Or fsModifiers

Finally modify the function bellow:

Public Function PreFilterMessage(ByRef m As System.Windows.Forms.Message) As Boolean Implements System.Windows.Forms.IMessageFilter.PreFilterMessage
Select Case (m.Msg)
If m.LParam.ToInt32 = _KeyMask Then
OnHotkeyPressed(New HotkeyEventArgs(_Key, _Modifier))
End If
End Select

Return False

End Function

Onve you make these changes it all works beautifully.

-- modified at 8:40 Saturday 29th October, 2005
GeneralRe: Excellent Control but a couple of problems Pin
Duncan Edwards Jones29-Oct-05 6:32
memberDuncan Edwards Jones29-Oct-05 6:32 
GeneralDisable the [Ctrl]+[Esc] keys Pin
Anonymous13-Jan-05 11:46
sussAnonymous13-Jan-05 11:46 
GeneralGreat but... Pin
Q_HAL2-Aug-04 4:36
memberQ_HAL2-Aug-04 4:36 
GeneralNice Ariticle:reason why I rated this excellent Pin
Ipog Gates18-Jan-04 0:45
memberIpog Gates18-Jan-04 0:45 
General.NET Version Pin
Merrion13-Jun-03 0:45
memberMerrion13-Jun-03 0:45 
GeneralRe: .NET Version Pin
Jehosephat22-Nov-04 10:34
memberJehosephat22-Nov-04 10:34 
GeneralRe: .NET Version Pin
Merrion22-Nov-04 12:14
memberMerrion22-Nov-04 12:14 

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