main_page.js

Todos.mainPage = SC.Page.design({
  mainPane: SC.MainPane.design({
    childViews: 'middleView'.w(),

    middleView: SC.ScrollView.design({
      childViews: 'contentView'.w(),

      contentView: SC.ListView.design({
        contentBinding: 'Todos.tasksController.arrangedObjects' //ADDED THIS
      })
    })
  })
});