计算属性——computed
2019-04-17 本文已影响0人
啊肉怪
computed与methods的区别
- computed是响应式的，methods并非响应式。
- 调用方式不一样，computed定义的成员像属性一样访问，methods定义的成员必须以函数形式调用。
- computed是带缓存的，只有其引用的响应式属性发生改变时才会重新计算，而methods里的函数在每次调用时都要执行。
- computed中的成员可以只定义一个函数作为只读属性，也可以定义get/set变成可读写属性，这点是methods中的成员做不到的
- computed是以对象的属性方式存在的，在视图层直接调用就可以得到值，例如：<div>{{msg}}</div>，而methods必须以函数形式调用，例如：<div>{{msg()}}</div>, 可见，computed直接以对象属性方式调用，而methods必须要函数执行才可以得到结果。
接下来让我们用实例来详细学习计算属行吧
案例一：购物车价格计算
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Vue.js computed——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: 50%;
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">
{{goods.name}}
</div>
<div class="item-img">
<img :src="goods.photo">
</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: {
show: false,
goodsList: [{
id: 1,
photo: 'img/iphone8.png',
name: 'iPhone8',
price: 6000,
count: 1,
link: 'https://item.jd.com/6784496.html'
}, {
id: 2,
photo: 'img/xiaomi9.png',
name: '小米9',
price: 3429,
count: 1,
link: 'https://item.jd.com/41563312675.html'
}, {
id: 3,
photo: 'img/huawei20.png',
name: '华为',
price: 5999,
count: 1,
link: 'https://item.jd.com/100000986050.html'
}]
},
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>
结果图
image
案例二——搜索页面，过滤器
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Vue.js computed练习-搜索页面的实现</title>
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<link rel="stylesheet" type="text/css" href="css/font-awesome.min.css" />
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style type="text/css">
.container {
width: 80%;
margin: 0 auto;
}
.input-box {
width: 50%;
height: 45px;
margin-bottom: 10px;
border-radius: 10px;
outline: none;
border: 1px solid #EEEEEE;
}
.item {
display: flex;
height: 200px;
border: 1px solid #eee;
border-radius: 8px;
margin-bottom: 8px;
margin-top: 10px;
}
.item-title {
flex: 1 1 70%;
}
.item-thumbnail {
flex: 1 1 30%
}
.item-thumbnail img {
width: 100%;
height: 100%;
border-bottom-right-radius: 5px;
border-top-right-radius: 5px;
}
a {
text-decoration: none;
color: black;
}
a:hover {
text-decoration: underline;
color: #FF0000;
}
i {
position: relative;
margin-left: -30px;
}
</style>
</head>
<body>
<div id="app">
<div class="container">
<input id="text" type="text" placeholder="请输入内容:" class="input-box" />
<i class="icon-search" @click="handleClick()"></i>
<div class="item" v-for="article in filteredArticles" v-show="show">
<a :href="article.url" class="item-title">
{{article.title}}
</a>
<div class="item-thumbnail">
<img :src="article.image">
</div>
</div>
<!-- <div v-show="showNone" class="showNone">
没有搜索到您需要的内容
</div> -->
</div>
</div>
<script type="text/javascript">
var app = new Vue({
el: '#app',
data: {
searchString: "",
show: true,
// showNone: false,
// 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://img.haomeiwen.com/i11438996/56b25f32c9307b4b?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://img.haomeiwen.com/i3973862/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://img.haomeiwen.com/i858154/015a4b083685a3d1.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://img.haomeiwen.com/i16042993/168b2cb17fd7ec0c?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://img.haomeiwen.com/i3525704/c7293758fc59e56b.jpg?imageMogr2/auto-orient/strip%7CimageView2/2/w/960/format/webp"
}
]
},
methods: {
handleClick: function() {
this.searchString = document.getElementById("text").value;
}
},
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) {
// this.showNone = true;
return articles_array;
}
//搜索关键词去除无用空格,转换为小写
searchString = searchString.trim().toLowerCase();
articles_array = articles_array.filter(function(item) {
//找到了标题还有searchString的文章
if (item.title.toLowerCase().indexOf(searchString) !== -1) {
return item;
}
})
// 返回转化后的数组
return articles_array;
}
}
})
</script>
</body>
</html>
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