Display an error or warning message. In order to decouple UI from this module,
this function justs trigger one 'message' event through event bus instead of
showing one message directly. It is UI module's resposiblity to listen this event
and show message.
Display an error or warning message. In order to decouple UI from this module, this function justs trigger one 'message' event through event bus instead of showing one message directly. It is UI module's resposiblity to listen this event and show message.