条件渲染的相关指令
一 概念
- v-if：值true会被渲染，值false不会被渲染
```html
<div id="app">
<div v-if='isShow'>div div div</div>
<button @click='isShow = !isShow'>改变</button>
</div>
<script>
new Vue({
el: '#app',
data: {
isShow: true
}
})
</script>
```
- v-else：与v-if结合使用形成对立面
```html
<div id="app">
<div v-if='isShow'>div div div</div>
<div v-else='isShow'>DIV DIV DIV</div>
<button @click='isShow = !isShow'>改变</button>
</div>
<script>
new Vue({
el: '#app',
data: {
isShow: true
}
})
</script>
```
- v-else-if：变量的多情况值判断
```html
<div id="app">
<div v-if='tag == 0'>if if if</div>
<div v-else-if='tag == 1'>else if else</div>
<div v-else='tag == 2'>else else else</div>
<input type='number' min='0' max='2' v-model='tag' />
</div>
<script>
new Vue({
el: '#app',
data: {
tag: 0
}
})
</script>
```
- template：不被渲染的vue结构标签
```html
<template v-if="isShow">
<p>用template嵌套</p>
<p>可以为多行文本</p>
<p>同时显隐</p>
<p>且template标签不会被vue渲染到页面</p>
</template>
```
- v-show：一定会被渲染到页面，以display属性控制显隐
- key：为v-if方式的显隐创建缓存，提高效率
```html
<div id="app">
<div v-if='tag == 0' key='0'>if if if</div>
<div v-else-if='tag == 1' key='1'>else if else</div>
<div v-else='tag == 2' key='2'>else else else</div>
<input type='number' min='0' max='2' v-model='tag' />
</div>
<script>
new Vue({
el: '#app',
data: {
tag: 0
}
})
</script>
```二 代码示范
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>条件渲染</title>
<script src="js/vue-2.5.17.js"></script>
<style type="text/css">
.box {
width: 200px;
height: 200px;
}
.r {background-color: red}
.o {background-color: orange}
</style>
<style type="text/css">
ul {
margin: 0;
padding: 0;
list-style: none;
}
.wrap, .main {
width: 500px;
height: 240px;
}
li {
float: left;
background-color: #666;
margin-right: 20px;
}
ul:after {
content: "";
display: block;
clear: both;
}
.red {background-color: red}
.green {background-color: green}
.blue {background-color: blue}
</style>
</head>
<body>
<div id="app">
<button @click="toggle">显隐切换</button>
<!-- v-if -->
<div class="box r" v-if="isShow"></div>
<!-- v-show -->
<div class="box o" v-show="isShow"></div>
<!-- 1.条件渲染的值为true|false -->
<!-- 2.true代表标签显示方式渲染 -->
<!-- 3.false v-if不渲染到页面,v-show以display:none渲染到页面,但也不会显示 -->
<!-- v-if v-else-if v-else -->
<ul>
<li @mouseover="changeWrap(0)">red</li>
<li @mouseover="changeWrap(1)">green</li>
<li @mouseover="changeWrap(2)">blue</li>
</ul>
<!-- red页面逻辑结构 -->
<div class="wrap red" v-if="tag == 0" key="0">...</div>
<!-- green页面逻辑结构 -->
<div class="wrap green" v-else-if="tag == 1" key="1">...</div>
<!-- blue页面逻辑结构 -->
<div class="wrap blue" v-else key="2">...</div>
<!-- v-if相关分支操作,在未显示情况下,是不会被渲染到页面中 -->
<!-- 通过key全局属性操作后,渲染过的分支会建立key对应的缓存,提高下一次渲染速度 -->
<ul>
<li @mouseover="changeMain(0)">red</li>
<li @mouseover="changeMain(1)">green</li>
<li @mouseover="changeMain(2)">blue</li>
</ul>
<!-- red页面逻辑结构 -->
<div class="main red" v-show="whoShow(0)">...</div>
<!-- green页面逻辑结构 -->
<div class="main green" v-show="whoShow(1)">...</div>
<!-- blue页面逻辑结构 -->
<div class="main blue" v-show="whoShow(2)">...</div>
</div>
</body>
<script type="text/javascript">
new Vue({
el: "#app",
data: {
isShow: false,
tag: 0,
flag: 0
},
methods: {
toggle () {
this.isShow = !this.isShow;
},
changeWrap (num) {
this.tag = num;
},
changeMain (num) {
// this.flag num
this.flag = num;
},
whoShow (num) {
// this.flag num
return this.flag == num;
}
}
})
</script>
</html>
