数据：三层嵌套

index.wxml 页面

!-- 菜单标签 --view class='menu_label'    view class='label_ul'        view wx:for="{{ menuList }}" wx:key='' class="{{ label_index == index ? 'label_lis' : 'label_li' }}" bindtap='menuList' id="{{ index }}"{{ item.title }}/view    /view/view!-- 图书内容 --view class='book_sec'    view class='book_ul' wx:for="{{ bookUl }}" wx:key='' wx:for-item="secUl"  wx:if="{{ label_index == index }}" id="{{ index }}"        view class='book_li' wx:for='{{ secUl.bookSec }}' wx:key='' wx:for-item="secLi"            view class='book_ol'                view class='book_ol_li' wx:for='{{ secLi.bookList }}' wx:key='' wx:for-item="item"                    view class='book_free b'免费阅读/view                    image src='{{ item.img }}'/image                    view class='book_people b'100006人在读/view                /view            /view        /view    /view/view

index.js页面

Page({        /**         * 页面的初始数据         */        data: {            menuList: [                { title: '全部' },                { title: '文学' },                { title: '技术类' },                { title: '社会科学' },                { title: '设计' },                { title: '技术类' },                { title: '社会科学' },            ],            label_index: 0,            bookUl: [                {                    bookSec: [                        {                            bookList: [                                { img: '../../img/img1_icon.png' },                                { img: '../../img/img2_icon.png' },                                { img: '../../img/img3_icon.png' },                            ]                        },                        {                            bookList: [                                { img: '../../img/img4_icon.png' },                                { img: '../../img/img5_icon.png' },                            ]                        }                    ]                },                {                    bookSec: [                        {                            bookList: [                                { img: '../../img/img6_icon.png' },                                { img: '../../img/img5_icon.png' },                                { img: '../../img/img4_icon.png' }                            ]                        },                        {                            bookList: [                                { img: '../../img/img7_icon.png' }                            ]                        }                    ]                },                {                    bookSec: [                        {                            bookList: [                                { img: '../../img/img7_icon.png' },                                { img: '../../img/img2_icon.png' },                                { img: '../../img/img1_icon.png' },                            ]                        },                        {                            bookList: [                                { img: '../../img/img3_icon.png' },                                { img: '../../img/img4_icon.png' },                                { img: '../../img/img6_icon.png' }                            ]                        }                    ]                },            ]                        /**             * 菜单点击切换内容             */                    menuList: function (e) {                let that = this;                // console.log(e);                var id = e.target.id;                                that.setData({                    label_index: id                })            }         },    })

如果列表中项目的位置会动态改变或者有新的项目添加到列表中，并且希望列表中的项目保持自己的特征和状态（如 input/ 中的输入内容，switch/ 的选中状态），需要使用 wx:key 来指定列表中项目的唯一的标识符。

如不提供 wx:key，会报一个 warning， 如果明确知道该列表是静态，或者不必关注其顺序，可以选择忽略。

wx:key 的值以两种形式提供
1）字符串，代表在 for 循环的 array 中 item 的某个 property，该 property 的值需要是列表中唯一的字符串或数字，且不能动态改变。
2）保留关键字 *this 代表在 for 循环中的 item 本身，这种表示需要 item 本身是一个唯一的字符串或者数字，如：
当数据改变触发渲染层重新渲染的时候，会校正带有 key 的组件，框架会确保他们被重新排序，而不是重新创建，以确保使组件保持自身的状态，并且提高列表渲染时的效率。

最后效果图