计算属性关键词：computed
- methods方法和computed的区别
methods和computed的区别.png
区别： - 可以使用 methods 来替代 computed
- computed 是基于它的依赖缓存，只有相关依赖发生改变时才会重新取值。而使用 methods ，在重新渲染的时候，函数总会重新调用执行。
- 使用 computed 性能会更好，但是如果你不希望缓存，可以使用 methods 属性
练习：购物车价格的计算
<html>
<head>
<meta charset="utf-8" />
<title>Vue.js computed练习——计算购物车总价</title>
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style type="text/css">
.container {
display: flex;
flex-direction: column;
width: 95%;
margin: 0 auto;
}
.item {
display: flex;
border: 1px solid #eee;
border-radius: 10px;
width: 95%;
height: 80px;
margin-bottom: 8px;
/* 垂直方向居中 */
align-items: center;
/* 水平方向居中 */
/* justify-content: center; */
padding-left: 10px;
padding-right: 10px;
}
.item-id {
flex: 1 1 10%;
}
.item-name {
flex: 1 1 20%;
}
.item-img {
flex: 1 1 20%
}
.item-img img {
width: 100%;
height: 100%;
}
.item-price {
flex: 1 1 15%;
}
.item-count {
flex: 1 1 35%;
}
.goods-count {
width: 20px;
text-align: center;
}
.settlement {
display: flex;
justify-content: space-between;
align-items: center;
}
.btn {
width: 100px;
height: 40px;
background-color: #FF5000;
border-radius: 10px;
border: none;
outline: none;
color: #FFF;
font-size: 16px;
}
</style>
</head>
<body>
<div id="app">
<div class="container">
<div class="item" v-for="goods in goodsList">
<div class="item-id">
{{goods.id}}
</div>
<div class="item-name">
<a :href="goods.url">{{goods.name}}</a>
</div>
<div class="item-img">
<img :src="goods.imgUrl">
</div>
<div class="item-price">
{{goods.price}}
</div>
<div class="item-count">
<button type="button" @click="goods.count-=1" :disabled="goods.count === 0">-</button>
<input type="text" class="goods-count" v-model="goods.count" />
<button type="button" @click="goods.count+=1">+</button>
</div>
</div>
<hr>
<div class="settlement">
<h3>总价：￥{{totalPrice}}</h3>
<button type="button" class="btn" @click="settlement()">结算</button>
</div>
<div class="result" v-if="show">
你购买了{{settlement}}件商品，需要支付总价为：{{totalPrice}}元
</div>
</div>
</div>
<script type="text/javascript">
var app = new Vue({
el: '#app',
data: {
goodsList: [{
id: 1,
name: 'iPhone 8',
url:'https://item.jd.com/6784500.html',
imgUrl: 'https://img14.360buyimg.com/n0/jfs/t17383/125/1470478028/71155/1cb53bc2/5acc5248N6a5f81cd.jpg',
price: 6000,
count: 1
},
{
id: 2,
name: 'iPhone X',
url:'https://item.jd.com/5089235.html',
imgUrl: 'https://img14.360buyimg.com/n0/jfs/t7297/154/3413903491/65679/45ae4902/59e42830N9da56c41.jpg',
price: 7000,
count: 1
},
{
id: 3,
name: 'iPhone xs Max',
url:'https://item.jd.com/100000287113.html',
imgUrl: 'https://img14.360buyimg.com/n0/jfs/t1/3/15/4536/138660/5b997bf8Ed72ebce7/819dcf182d743897.jpg',
price: 8000,
count: 1
}
],
show: false
},
methods: {},
computed: {
totalPrice: function() {
var totalPrice = 0;
var len = this.goodsList.length;
for (var i = 0; i < len; i++) {
totalPrice += this.goodsList[i].price * this.goodsList[i].count;
}
return totalPrice;
},
settlement: function() {
this.show = true;
var totalCount = 0;
var len = this.goodsList.length;
for (var i = 0; i < len; i++) {
totalCount += this.goodsList[i].count;
}
return totalCount;
}
}
})
</script>
</body>
</html>
购物车.png
练习： 搜索页面
<html>
<head>
<meta charset="utf-8" />
<title>Vue.js computed练习-搜索页面的实现</title>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style type="text/css">
.container {
width: 90%;
margin: 0 auto;
}
.input-box {
width: 50%;
height: 25px;
margin-bottom: 10px;
}
.item {
display: flex;
height: 100px;
border: 1px solid #eee;
border-radius: 8px;
margin-bottom: 8px;
}
.item-title {
flex: 1 1 80%;
}
.item-thumbnail {
flex: 1 1 20%
}
.item-thumbnail img {
width: 100%;
height: 100%;
}
</style>
</head>
<body bgcolor="lightpink">
<body>
<div id="app">
<div class="container">
<span>
<input type="text" v-model="searchString" placeholder="请输入搜索内容" class="input-box" /><input type="button" class="btn" value="搜索🔍"/>
</span>
<div class="item" v-for="article in filteredArticles">
<a :href="article.url" class="item-title">
{{article.title}}
</a>
<div class="item-thumbnail">
<img :src="article.image">
</div>
</div>
</div>
</div>
<script type="text/javascript">
var app = new Vue({
el: '#app',
data: {
searchString: "",
// 数据模型
articles: [{
"title": "堪称神器的3款在线工具，你一定用得上！",
"url": "https://www.jianshu.com/p/e83e7999346b",
"image": "https://upload-images.jianshu.io/upload_images/11438996-56b25f32c9307b4b?imageMogr2/auto-orient/strip%7CimageView2/2/w/640/format/webp"
},
{
"title": "经典面试题：从 URL 输入到页面展现到底发生什么？",
"url": "https://www.jianshu.com/p/45ba3e0d0c7e",
"image": "https://upload-images.jianshu.io/upload_images/3973862-d90954249a6f6ccd.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1000/format/webp"
},
{
"title": "如何免翻墙使用谷歌搜索和Chrome应用商店",
"url": "https://www.jianshu.com/p/484f8e6c88f6",
"image": "https://upload-images.jianshu.io/upload_images/858154-015a4b083685a3d1.jpg?imageMogr2/auto-orient/strip%7CimageView2/2/w/800/format/webp"
},
{
"title": "四款前所未有好用的黑科技APP，绝对的良心实用，赶紧告诉家人",
"url": "https://www.jianshu.com/p/2aec84d269fe",
"image": "https://upload-images.jianshu.io/upload_images/16042993-168b2cb17fd7ec0c?imageMogr2/auto-orient/strip%7CimageView2/2/w/640/format/webp"
},
{
"title": "坚持学英语的方法有哪些",
"url": "https://www.jianshu.com/p/0a6a61b0933c",
"image": "https://upload-images.jianshu.io/upload_images/3525704-c7293758fc59e56b.jpg?imageMogr2/auto-orient/strip%7CimageView2/2/w/960/format/webp"
}
]
},
computed: {
// 计算函数，匹配搜索
filteredArticles: function() {
var articles_array = this.articles,
searchString = this.searchString;
//搜索关键词为空,则返回原始数据集
if (!searchString) {
return articles_array;
}
//搜索关键词去除无用空格,转换为小写
searchString = searchString.trim().toLowerCase();
//过滤数组中每个元素,如果
articles_array = articles_array.filter(function(item) {
if (item.title.toLowerCase().indexOf(searchString) !== -1) {
return item;
}
})
// 返回转化后的数组
return articles_array;;
}
}
})
</script>
</body>
</html>
搜索.png
