this.listenTo(this.collection, 'add', this.renderBook);renderBook: function (item) {        var bookView = new app.BookView({            model: item        });        this.$el.append(bookView.render().el);}

当我们给collection添加一个model的时候，如果绑定了collection的add事件，那么该事件的回调函数会接收三个参数。

第一个参数是：当前被add到collection的model对象；

第二个参数是：当前collection对象。

第三个参数是可选项，具体是什么官方也没有介绍。

其它的事件回调类似。以下附上官方事件列表。

• "add" (model, collection, options) — when a model is added to a collection.
• "remove" (model, collection, options) — when a model is removed from a collection.
• "reset" (collection, options) — when the collection's entire contents have been replaced.
• "sort" (collection, options) — when the collection has been re-sorted.
• "change" (model, options) — when a model's attributes have changed.
• "change:[attribute]" (model, value, options) — when a specific attribute has been updated.
• "destroy" (model, collection, options) — when a model is .
• "request" (model, xhr, options) — when a model (or collection) has started a request to the server.
• "sync" (model, resp, options) — when a model (or collection) has been successfully synced with the server.
• "error" (model, xhr, options) — when a model's  call fails on the server.
• "invalid" (model, error, options) — when a model's  fails on the client.
• "route:[name]" (params) — Fired by the router when a specific route is matched.
• "route" (router, route, params) — Fired by history (or router) when any route has been matched.
• "all" — this special event fires for any triggered event, passing the event name as the first argument.