无法有条件地渲染视图木偶

我不知道如何使用函数来决定在木偶中渲染哪个子视图。根据这里的文档,它似乎应该非常简单: https://marionettejs.com/docs/master/marionette.collectionview.html#collectionviews-childview

我发现复合视图文档中的页面推断使用函数定义子视图应该与集合视图和复合视图相同 https://marionettejs.com/docs/master/marionette.compositeview.html#compositeviews-childview )

然而,通过以下代码,我得到了错误消息“Uncaught TypeError:view.on不是函数”我的代码如下:

var Backbone = require('backbone');
var Marionette = require('backbone.marionette');

var ToDoModel = require('./models/todo');

var ToDo = Marionette.LayoutView.extend({
  tagName: 'li',
  template: require('./templates/todoitem.hbs')
});


var TodoList = Marionette.CompositeView.extend({
  el: '#app-hook',
  template: require('./templates/todolist.html'),

  childView: function(item) {
    return ToDo;
  },
  childViewContainer: 'ul',

  ui: {
    assignee: '#id_assignee',
    form: 'form',
    text: '#id_text'
  },

  triggers: {
    'submit @ui.form': 'add:todo:item'
  },

  collectionEvents: {
    add: 'itemAdded'
  },

  modelEvents: {
    invalid: 'itemInvalid'
  },

  onAddTodoItem: function() {
    this.model.set({
      assignee: this.ui.assignee.val(),
      text: this.ui.text.val()
    });

    if (this.model.isValid()) {
      var items = this.model.pick('assignee', 'text');
      this.collection.add(items);
    }
  },

  itemAdded: function() {
    this.model.set({
      assignee: '',
      text: ''
    });

    this.ui.assignee.val('');
    this.ui.text.val('');
  },

  itemInvalid: function() {
    console.log('this item is invalid!')
  }

});


var todo = new TodoList({
  collection: new Backbone.Collection([
    {assignee: 'Scott', text: 'Write a book about Marionette'},
    {assignee: 'Andrew', text: 'Do some coding'}
  ]),
  model: new ToDoModel()
});

todo.render();

为什么不呈现ToDo视图?