@Command //@Command annotates a command method 
	@NotifyChange({"selectedTodo","subject"}) //@NotifyChange annotates data changed notification after calling this method 
	public void addTodo(){
		if(Strings.isBlank(subject)){
			Clients.showNotification("Subject is blank, nothing to do ?");
		}else{
			//save data
			selectedTodo = todoListService.saveTodo(new Todo(subject));
			//update the model, by using ListModelList, you don't need to notify todoListModel change
			//it is efficient that only update one item of the listbox
			todoListModel.add(selectedTodo);
			todoListModel.addToSelection(selectedTodo);
			
			//reset value for fast typing.
			subject = null;
		}
	}