def createMainWidget(argv):
    """
    Function to create the main widget.
    
    @param argv list of commandline parameters (list of strings)
    @return reference to the main widget (QWidget)
    """
    from Tools.UIPreviewer import UIPreviewer
    if len(argv) > 1:
        fn = argv[1]
    else:
        fn = None
    previewer = UIPreviewer(fn, None, 'UIPreviewer')
    return previewer
