A question about creating toolbar in childframe with MFC

protected:
    CMFCToolBar       m_wndChildToolBar;

public:
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);

BEGIN_MESSAGE_MAP(CChildFrame, CMDIChildWndEx)
    ON_WM_CREATE()
END_MESSAGE_MAP()

int CChildFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CMDIChildWndEx::OnCreate(lpCreateStruct) == -1)
        return -1;
    if (!m_wndChildToolBar.CreateEx(this, TBSTYLE_FLAT,WS_OVERLAPPED| WS_CHILD | WS_VISIBLE | CBRS_LEFT | CBRS_GRIPPER | CBRS_TOOLTIPS | CBRS_FLYBY | CBRS_SIZE_DYNAMIC) ||
        !m_wndChildToolBar.LoadToolBar(IDR_TOOLBAR1))
    {
        TRACE0("Failed to create toolbar\n");
        return -1;      // fail to create
    }
    // TODO:  Add your specialized creation code here
    m_wndChildToolBar.EnableDocking(CBRS_ALIGN_ANY);
    EnableDocking(CBRS_ALIGN_ANY);

    DockPane(&m_wndChildToolBar);
    return 0;
}