WindowImplBase::OnSysCommand-------duilib在最大化和还原间切换

virtual	LRESULT OnSysCommand(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
	{
		if( wParam == SC_CLOSE ) {
			::PostQuitMessage(0L);
			bHandled = TRUE;
			return 0;
		}
		BOOL bZoomed = ::IsZoomed(*this);
		LRESULT lRes = CWindowWnd::HandleMessage(uMsg, wParam, lParam);
		if( ::IsZoomed(*this) != bZoomed ) {
			if( !bZoomed ) {
				CControlUI* pControl = static_cast<CControlUI*>(m_PaintManager.FindControl(_T("maxbtn")));
				if( pControl ) pControl->SetVisible(false);
				pControl = static_cast<CControlUI*>(m_PaintManager.FindControl(_T("restorebtn")));
				if( pControl ) pControl->SetVisible(true);
			}
			else {
				CControlUI* pControl = static_cast<CControlUI*>(m_PaintManager.FindControl(_T("maxbtn")));
				if( pControl ) pControl->SetVisible(true);
				pControl = static_cast<CControlUI*>(m_PaintManager.FindControl(_T("restorebtn")));
				if( pControl ) pControl->SetVisible(false);
			}
		}
		return lRes;
	}