Prevent Windows Suspend Mode

Category:

System/API

Type:

Snippets

Difficulty:

Intermediate

Author:

Merrion Computing

Version Compatibility: Visual Basic 6, Visual Basic 5

More information:

Most laptop PCs (and some green desktop PCs) will go into a suspended mode to reduce their power consumption after a preset period of user inactivity. However this may interfere with the normal operation of your application if it is watching a named pipe or performing a long operation etc.

The following code prevents windows (NT/2000 and 9x) going into suspended mode.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
'In a Module Option Explicit Public oldProcAddress As Long Public Enum enPowerBroadcastType PBT_APMQUERYSUSPEND = &H0 PBT_APMQUERYSTANDBY = &H1 PBT_APMQUERYSUSPENDFAILED = &H2 PBT_APMQUERYSTANDBYFAILED = &H3 PBT_APMSUSPEND = &H4 PBT_APMSTANDBY = &H5 PBT_APMRESUMECRITICAL = &H6 PBT_APMRESUMESUSPEND = &H7 PBT_APMRESUMESTANDBY = &H8 End Enum Public Const BROADCAST_QUERY_DENY = &H424D5144 Public Const WM_POWER = &H48 Public Const WM_POWERBROADCAST = &H218 Public Const PWR_SUSPENDREQUEST = 1 Public Const GWL_WNDPROC = (-4) Public Const PWR_FAIL = (-1) Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long Public 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

Code:

'\\ In a .BAS file:
'\\ --[VB_WindowProc]--------------------------------------------
'\\ 'typedef LRESULT (CALLBACK* WNDPROC)(HWND, UINT, WPARAM, 
'\\ LPARAM);
'\\ Parameters:
'\\ hwnd - window handle receiving message
'\\ wMsg - The window message (WM_..etc.)
'\\ wParam - First message parameter
'\\ lParam - Second message parameter
'\\ Note:
'\\ When subclassing a window proc using this, set the
'\\  eventhandlerhOldWndProc property to the window's previous 
'\\ window proc address.
'\\ -------------------------------------------------------------'\\ You have a royalty free right to use, reproduce, modify, 
'\\ publish and mess with this code
'\\ I'd like you to visit http://www.merrioncomputing.com for
'\\  updates, but won't force you
'\\ ----------------------------------------------------------

Public Function VB_WindowProc(ByVal hWnd As Long, ByVal wMsg As _
  Long, ByVal wParam As Long, ByVal lParam As Long) As Long

On Local Error Resume Next
Dim lRet As Long

'\\ If its a power suspending broadcast, kill it...
If wMsg = WM_POWER And wParam = PWR_SUSPENDREQUEST Then
   '\\ This is the message in Windows NT/2000
    VB_WindowProc = PWR_FAIL
ElseIf wMsg = WM_POWERBROADCAST And wParam = _
      PBT_APMQUERYSUSPEND Then
    VB_WindowProc = BROADCAST_QUERY_DENY
Else
VB_WindowProc = CallWindowProc(oldProcAddress, hWnd, wMsg,_
       wParam, lParam)
End If

End Function

'\\ In your app's MAIN form:
Private Sub Form_Load()

oldProcAddress = SetWindowLong(Me.hWnd, GWL_WNDPROC, _
      AddressOf VB_WindowProc)

End Sub

Private Sub Form_Unload(Cancel As Integer)

Call SetWindowLong(Me.hWnd, GWL_WNDPROC, oldProcAddress)

End Sub