To create the modeless dialog as sibling, follow this link.

Follow these steps:

1. Create a new dialog resource and use the Class Wizard for making a new CDialog based class for it; let's call it CDropDialog
2. In your CFormView-derived class, add a (private) member variable of type CDropDialog* as a container for the modeless dialog class, let's call it m_pModeless. In the constructor of your view, make sure you initialize m_pModeless to NULL
3. In your appropriate message handler, let's call it OnModeless, do the following:

   void CInterfaceView::OnModeless() 
   {
       // Display the modal dialog box
   
       if (!m_pModeless)
           m_pModeless = new CDropDialog;
   
       if (!::IsWindow(m_pModeless->GetSafeHwnd()))
           m_pModeless->Create(IDD_DIALOG1, this);
   
       m_pModeless->ShowWindow(SW_SHOW); 
   }

CInterfaceView::~CInterfaceView()
{
    if (m_pModeless)
    {
        if (::IsWindow(m_pModeless->GetSafeHwnd()))
            m_pModeless->EndDialog(IDCANCEL);
        delete m_pModeless;
    }
}