十三、Vue条件渲染v-for遍历数据

for循环，经常使用到的一种循环结构，那么vue中也是如此，v-for指令基于一个数组来渲染一个列表，其语法格式为item in imtes，其中items是源数据源数组，而item是被迭代的数组元素的别名。

v-for渲染一个基于数组的列表

<span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">div</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">id</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"app"</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(84, 110, 122)"><!--基本渲染--></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">v-for</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"item in items"</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">:key</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"item.name"</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span>{{ item.name}}<span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(84, 110, 122)"><!--带索引的渲染，索引从0开始--></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">v-for</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"(item,index) in items"</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span>{{ index }} - {{ item.name }}<span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">div</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">script</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(199, 146, 234)">var</span> <span style="box-sizing: border-box">app</span> <span style="box-sizing: border-box">=</span> <span style="box-sizing: border-box;color: rgb(199, 146, 234)">new</span> <span style="box-sizing: border-box;color: rgb(130, 177, 255)">Vue</span>({</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span style="box-sizing: border-box;color: rgb(128, 203, 174)">el</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"#app"</span>,</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span style="box-sizing: border-box;color: rgb(128, 203, 174)">data</span>:{</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">            <span style="box-sizing: border-box;color: rgb(128, 203, 174)">items</span>:[</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">                {<span style="box-sizing: border-box;color: rgb(128, 203, 174)">name</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"PHP"</span>},</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">                {<span style="box-sizing: border-box;color: rgb(128, 203, 174)">name</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"Vue"</span>},</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">                {<span style="box-sizing: border-box;color: rgb(128, 203, 174)">name</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">'JavaScript'</span>}</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">            ]</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        }</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    });</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">script</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span>

v-for渲染一个基于对象的列表

<span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">div</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">id</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"app"</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span> <span style="box-sizing: border-box;color: rgb(255, 203, 107)">v-for</span>=<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"v in object"</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span>{{ v }}<span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">li</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">ul</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">div</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"><</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">script</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(199, 146, 234)">var</span> <span style="box-sizing: border-box">app</span> <span style="box-sizing: border-box">=</span> <span style="box-sizing: border-box;color: rgb(199, 146, 234)">new</span> <span style="box-sizing: border-box;color: rgb(130, 177, 255)">Vue</span>({</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span style="box-sizing: border-box;color: rgb(128, 203, 174)">el</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">"#app"</span>,</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        <span style="box-sizing: border-box;color: rgb(128, 203, 174)">data</span>:{</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">            <span style="box-sizing: border-box;color: rgb(128, 203, 174)">object</span>:{</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">                <span style="box-sizing: border-box;color: rgb(128, 203, 174)">title</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">'自如初'</span>,</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">                <span style="box-sizing: border-box;color: rgb(128, 203, 174)">desc</span>:<span style="box-sizing: border-box;color: rgb(195, 232, 141)">'一个专注于技术的博客'</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">            }</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">        }</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">    });</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)"></</span><span style="box-sizing: border-box;color: rgb(255, 83, 112)">script</span><span class="cm-tag cm-bracket" style="box-sizing: border-box;color: rgb(255, 83, 112)">></span></span>

v-for中key属性

在渲染基于数组的列表中，可以看到:key，那么它有什么作用？官方文档中是这样介绍的：

key 的特殊 attribute 主要用在 Vue 的虚拟 DOM 算法，在新旧 nodes 对比时辨识 VNodes。如果不使用 key，Vue 会使用一种最大限度减少动态元素并且尽可能的尝试就地修改/复用相同类型元素的算法。而使用 key 时，它会基于 key 的变化重新排列元素顺序，并且会移除 key 不存在的元素。

有相同父元素的子元素必须有独特的 key。重复的 key 会造成渲染错误。

key值得作用：增加唯一性,更高效的更新虚拟DOM，便于diff算法的更新，key值得唯一性更快的更新虚拟DOM。

diff算法对DOM进行原地复用，减少DOM性能耗费。

简单的来说，这个key就是为了保证这个值在这个数组中是唯一的。

我是小白，期待和优秀的你一起同行!

小白

2020年12月03日