'On click ok, change the workspace in the app with out selection
and destroy.'

def on_click_ok(self, button=None):

    selection = self.ws_view.get_selection()
    (model, iter_) = selection.get_selected()
    if (model and iter_):
        ws_name = model[iter_][0]
        self.change_ws_callback(ws_name)
        self.destroy()
