how to show only a image without a text for a toolitem in toolbar?

[明覺 <shi minjue gmail com>]

I created a toolbar by this string:
    Glib::ustring ui_info =
    "<ui>"
    "  <toolbar name='ToolBar'>"
    "    <toolitem action='NewSurface'/>"
    "    <toolitem action='ImportSurface'/>"
    "    <toolitem action='ExportSurface'/>"
    "  </toolbar>"
    "</ui>";
it will show a image with a text below it for each toolitem, how could
i remove the text below the image? thanks


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