Create a modeless dialog box as sibling of the app's main window

It's nearly as short as the child version of modeless dialogs

Follow these steps:

1. Create a new dialog resource and use the Class Wizard for making a new CDialog based class COtherDropDialog
2. In the class maintaining the modeless dialog (here it's CInterfaceView) add a member variable of type pointer to CWinThread and make sure you have a destructor:

   <font color="#000080">class</font> CInterfaceView : public CView
   {
   ...
       CWinThread *m_pDlgThread
       ~CInterfaceView();
   ...
   }

3. Use ClassWizard to create a new CWinThread-based class COtherDropDialogThread
4. Override COtherRopDialogThread::InitInstance():
   If you forget to change the m_pMainWnd variable, the dialog will stay modal!

   BOOL COtherDropDialogThread::InitInstance()
   {
       COtherDropDialog dlg;
   
       m_pMainWnd = &dlg;
       dlg.DoModal();  <font color="#008000">// returning false will make MFC doing the cleanup for us :)</font>
             
       return FALSE;
   }

5. In your appropriate message handler, do the following:

   <FONT COLOR=#008080>void</FONT> CInterfaceView::OnFileOthermodeless() 
   {
       <FONT COLOR=#008000>// this block determines if we have our dialog already</FONT>
       <FONT COLOR=#008000>// displayed and not yet closed. You can't rely on </FONT>
       <FONT COLOR=#008000>// m_pDlgThread to be NULL, because if you already have displayed </FONT>
       <FONT COLOR=#008000>// and closed it, the pointer is not NULL but invalid	 </FONT>
       <FONT COLOR=#804040>if</FONT> (AfxIsValidAddress(m_pDlgThread, <FONT COLOR=#804040>sizeof</FONT>(CWinThread)) &&
           AfxIsValidAddress(m_pDlgThread->m_pMainWnd, <FONT COLOR=#804040>sizeof</FONT>(CWnd)))
       {
           <FONT COLOR=#804040>if</FONT> (::IsWindow(m_pDlgThread->m_pMainWnd->GetSafeHwnd()))
           {    m_pDlgThread->GetMainWnd()->SetWindowPos(
   	                &wndTop, <FONT COLOR=#aa6400>0</FONT>,<FONT COLOR=#aa6400>0</FONT>,<FONT COLOR=#aa6400>0</FONT>,<FONT COLOR=#aa6400>0</FONT>,SWP_NOMOVE|SWP_NOSIZE|SWP_SHOWWINDOW);
                <FONT COLOR=#804040>return</FONT>;
           }
       }
       <FONT COLOR=#008000>// OK, we need to create a new thread</FONT>
       m_pDlgThread=AfxBeginThread( RUNTIME_CLASS(COtherDropDialogThread) );	
   }
   
   

6. If you like your top-level window to have an icon displayed in the taskbar, add the following to COtherDropDialog:: OnInitDialog (ommited in the sample):

   BOOL COtherDropDialog::OnInitDialog() 
   {
       CDialog::OnInitDialog();
       m_hIcon = AfxGetApp()->LoadIcon(IDI_MYICON);
       SetIcon(m_hIcon, TRUE);
       SetIcon(m_hIcon, FALSE);
   <font color="#008000">    // and all the other stuff
       //...
   </font>}

7. Don't forget to do the clean-up in the destructor:

   CInterfaceView::~CInterfaceView()
   {
       <font color="#000080">if</font> (AfxIsValidAddress(m_pDlgThread, <font color="#000080">sizeof</font>(CWinThread)) &&
   	AfxIsValidAddress(m_pDlgThread->m_pMainWnd, <font color="#000080">sizeof</font>(CWnd)))
       {
   	// retrieve the threads main window
   	CDialog *pDlg = (CDialog *)m_pDlgThread->m_pMainWnd;
   
   	<font color="#000080">if</font> (::IsWindow(pDlg->GetSafeHwnd()))
   	{
   <font color="#008000">	    // make sure we have a CDialog-derived main 
   	    // thread window then terminate it
   </font>	    ASSERT(pDlg->IsKindOf(RUNTIME_CLASS(CDialog)));
   	    pDlg->EndDialog(IDCANCEL);
   
   <font color="#008000">	    // now give the thread some time to end, 
   	    // 2 second should be enough. You may 
   	    // able to use INFINITE as wait value, if you dare...
   </font>	    WaitForSingleObject(m_pDlgThread->m_hThread, 2000);
   	    m_pDlgThread=NULL;
   	}
       }
   }