From: mayayana on
Here's a sample of SetWinEventHook. I don't know
what issues might be involved with a server-hosted
program. You'd need to test that. It seems to work fine
for me testing it locally.
Basically this sets up a system-wide hook that informs
you when the focused window is changing. The callback
includes the hWnd of the window involved, so you can
easily tell whether your window is involved.

You can actually get event notification for specific
ranges of events. The first two parameters of the
function give the lower and upper range of constant
value to monitor. By setting both values to SYS_FOREGROUND
you should only be informed when the foreground
window changes.

One note: Don't do anything like put a msgbox
in the event sub. That could catch you in a loop
of focus - msgbox - focus -msgbox - etc.

Code in form named F1:
Friend Sub GettingFocus(IfFocused As Boolean)
'-- F1 has a label named Lab1
Lab1.Caption = CStr(IfFocused)
End Sub

Private Sub Form_Load()
End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
End Sub
'----------------end form code -----------

'------- code in .bas module ---------------
Public Const SYS_FOREGROUND = 3&
Public Declare Function SetWinEventHook Lib "user32.dll" (ByVal eventMin As
Long, ByVal eventMax As Long, ByVal hmodWinEventProc As Long, ByVal
pfnWinEventProc As Long, ByVal idProcess As Long, ByVal idThread As Long,
ByVal dwFlags As Long) As Long
Public Declare Function UnhookWinEvent Lib "user32.dll" (ByVal LHandle As
Long) As Long

Public LHook As Long

Public Sub StartEventHook()
LHook = SetWinEventHook(SYS_FOREGROUND, SYS_FOREGROUND, 0&, AddressOf
WinEventFunc, 0, 0, 0)
End Sub

Public Sub StopEventHook()
Dim LRet As Long
If LHook = 0 Then Exit Sub
LRet = UnhookWinEvent(LHook)
End Sub

Public Function WinEventFunc(ByVal HookHandle As Long, ByVal LEvent As Long,
ByVal hWnd As Long, ByVal idObject As Long, ByVal idChild As Long, ByVal
idEventThread As Long, ByVal dwmsEventTime As Long) As Long
If hWnd = F1.hWnd Then
F1.GettingFocus True
F1.GettingFocus False
End If
End Function
'---------end .bas code ------------------

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