about child dialog in taskpanel

in the demo "ToolBox",I add some code in order to add a child dialog in the taskpanel,but it can not display

CXTPTaskPanelGroup* pFolderWindows = m_wndTaskPanel.AddGroup (ID_TOOLBOXFOLDER_GENERAL);
 m_wndTaskPanel.SetTheme(xtpTaskPanelThemeNativeWinXPPl ain);
 CTaskPanelDlg m_dlgSize;  //the CTaskPanelDlg works well in the demo TaskPanel,
 m_dlgSize.Create(IDD_MYDLG, &m_wndTaskPanel);//IDD_MYDLG is the dialog resource with a child properte;
 CXTPTaskPanelGroupItem* pItem = pFolderWindows->AddControlItem(m_dlgSize);
 pItem->GetMargins().SetRect(0, 0, 0, 0);
 m_dlgSize.SetItem(pItem); pFolderWindows->SetE xpanded(TRUE);

maybe some mistake is made,but I don't know where.

thx,I have solved the problem,

CTaskPanelDlg m_dlgSize; //here the object is a local variable,should be declared a member of CMainFrame