MFC Document changed

Hi everyone,
I created a MFC MDI Application. I want to manage it in order to check, every time a View get focus, that its Document has been changed or not (for example using another hinstance of the same application or a text editor), notifying with a MessageBox something like this "(file name): this file has been modified by another program, do you want to reload it?".
How can I manage this behaviour?

Thanks a lot for your help.

You can handle WM_MDIACTIVATE message and get the last modified time of the document's file.
Example

Code:

---

void CChildFrame::OnMDIActivate(BOOL bActivate, CWnd* pActivateWnd, CWnd* pDeactivateWnd)
{
  CMDIChildWnd::OnMDIActivate(bActivate, pActivateWnd, pDeactivateWnd);
       
  if(bActivate)
  {
      CDocument* pDoc = ((CFrameWnd*)pActivateWnd)->GetActiveDocument();
      const CString& strFile = pDoc->GetPathName();
      if(!strFile.IsEmpty())
      {
        CFileStatus fileStatus;
        VERIFY(CFile::GetStatus(strFile, fileStatus));
        CTime m_TimeModified = fileStatus.m_mtime;
        // Next, compare the actual modified time with last modified time,
        // which may be one previously stored in document's class.
        // ...
      }
  }
}

---

It works, except that this update is not on application focus, but on Document switching. Anyway, I put this code in CMainFrame::OnActivateApp and it works perfectly!
Thanks a lot.