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MDI application - switch between documents

In an MDI application, can I know when the user switches between documents? More precisely, can a document know when it becomes active and/or inactive?

The reason I want this is the following: when working with a document, a user can call a modeless dialog which displays some info for him. Since the dialog is modeless, the user can then open another document. However, because it is still a dialog, its "priority" is higher than that any view. I want to write something like this:

  if (Dialog && IsWindow(Dialog->m_hWnd))

  if (Dialog && IsWindow(Dialog->m_hWnd))

Is it at all possible?
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1 Solution
I believe you'll have to handle the WM_ACTIVATE message in the MDI child window. The window should receive that message whenever the window gets the focus in the application.
// This is a delphi routine, so hopefully you can translate it...

Procedure WndProc(var Message: TMessage);
  if Message.Msg=WM_Activate then begin
    // Do something with NotActive here...

Value of the low-order word of wParam. Specifies whether the window is being activated or deactivated. This parameter can be one of the following values:

Value      Meaning
WA_ACTIVE      Activated by some method other than a mouse click (for example, by a call to the SetActiveWindow function or by use of the keyboard interface to select the window).
WA_CLICKACTIVE      Activated by a mouse click.
WA_INACTIVE      Deactivated.

// Here's what TMessage should look like...
  TMessage = packed record
    Msg: Cardinal;
    case Integer of
      0: (
        WParam: Longint;
        LParam: Longint;
        Result: Longint);
      1: (
        WParamLo: Word;
        WParamHi: Word;
        LParamLo: Word;
        LParamHi: Word;
        ResultLo: Word;
        ResultHi: Word);
LeschaAuthor Commented:
Correct except for the "click" part. MFC doesn't have this distinction. Never mind, I don't this distinction, anyway.

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