Detecting (in VBA) when the window containing an excel instance becomes active

Question

I can see the WindowActivate events firing, at various levels, when I switch between windows within excel, but is there a way to fire an event when excel become

Answer 1

I modified @AndASM 's very nice solution to work in a 64 bit environment. Changes were

• changed API function call parameters from Long to LongLong parameters
• included PtrSafe attributes
• replaced Sheet1.[A1] = with range("a1").value = syntax

@andasm's code with mods follows

Option Explicit

Private Const EVENT_SYSTEM_FOREGROUND = &H3&
Private Const WINEVENT_OUTOFCONTEXT = 0

Private Declare PtrSafe Function SetWinEventHook Lib "user32.dll" (ByVal eventMin As Long, _
ByVal eventMax As Long, _
ByVal hmodWinEventProc As LongLong, _
ByVal pfnWinEventProc As LongLong, _
ByVal idProcess As Long, _
ByVal idThread As Long, _
ByVal dwFlags As Long) As Long
Private Declare PtrSafe Function GetCurrentProcessId Lib "kernel32" () As Long
Private Declare PtrSafe Function GetWindowThreadProcessId Lib "user32" (ByVal hWnd As Long, lpdwProcessId As Long) As Long

Private pRunningHandles As Collection

Public Function StartEventHook() As Long
  If pRunningHandles Is Nothing Then Set pRunningHandles = New Collection
  StartEventHook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND, EVENT_SYSTEM_FOREGROUND, 0&, AddressOf WinEventFunc, 0, 0, WINEVENT_OUTOFCONTEXT)
  pRunningHandles.Add StartEventHook
End Function

Public Sub StopEventHook(lHook As Long)
  Dim LRet As Long
  If lHook = 0 Then Exit Sub

  LRet = UnhookWinEvent(lHook)
End Sub

Public Sub StartHook()
    StartEventHook
End Sub

Public Sub StopAllEventHooks()
  Dim vHook As Variant, lHook As Long
  For Each vHook In pRunningHandles
    lHook = vHook
    StopEventHook lHook
  Next vHook
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
  'This function is a callback passed to the win32 api
  'We CANNOT throw an error or break. Bad things will happen.
  On Error Resume Next
  Dim thePID As Long

  If LEvent = EVENT_SYSTEM_FOREGROUND Then
    GetWindowThreadProcessId hWnd, thePID
    If thePID = GetCurrentProcessId Then
      Application.OnTime Now, "Event_GotFocus"
    Else
      Application.OnTime Now, "Event_LostFocus"
    End If
  End If

  On Error GoTo 0
End Function

Public Sub Event_GotFocus()
    Range("a1").Value = "Got Focus"
End Sub

Public Sub Event_LostFocus()
   Range("a1").Value = "Nope"
End Sub