day07 computed方法

作者: 黑桃_06ea | 来源:发表于2019-03-15 13:40 被阅读0次

day07 computed方法
七、computed的使用 ------ 2020-05-07
5.计算属性
【Vue】举例解析Vue中computed与method的区别
8.computed和methods的区别
computed && watch && methods
vue2.0不再支持v-html中使用过滤器了怎么办？
2017/09/15 VUE class与style绑定
computed, watch, created, mounte
Vue中 computed、methods和watch的区别

computed和methods

在vue.js中，有methods和computed两种方式来动态当作方法来用的:首先最明显的不同就是调用的时候，methods要加上（）;我们可以使用 methods 来替代 computed，效果上两个都是一样的，但是 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

代码

<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
        <title>computed练习</title>
        <!-- 开发环境版本，包含了有帮助的命令行警告 -->
        <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    </head>
    <body>
        <!-- vue-app的根容器 -->
        <div id="app">
            
            <button type="button" @click="show2">调用methods</button>
            <button tuype="button" @click="show1">调用computed</button>
        </div>
        <script type="text/javascript">
            var app=new Vue({
                el:'#app',
                data:{
                    name1:'methods',
                    name2:'这是Vue.jsd的computed计算练习'
                },
                methods:{
                    show2:function(){
                        alert(this.name1);
                        
                    }
                    },
                computed:{
                    show:function(){
                        alert(this.name2);
                        
                    }
                }   
                
            })
        </script>
    </body>
</html>

简单购物车

<html>
    <head>
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
        <title></title>
        <title>购物车练习</title>
        <!-- 开发环境版本，包含了有帮助的命令行警告 -->
        <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
        <style type="text/css">
            .a{
                width: 40%;
                margin: 0 auto;
            }
            .container{
                display: flex;
                flex-direction: column;
            }
            .item{
                display: flex;
                border: 1px solid #008000;
                border-radius: 10px;
                width: 350px;
                height: 50px;
                margin-bottom: 10px;
                /* 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 20%;
            }
            .item-name{
                flex: 1 1 20%;
            }
            .item-price{
                flex: 1 1 30%;
            }
            .item-count{
                /* display: flex; */
                flex: 1 1 30%;
            }
            .goods-count{
                width: 15px;
            }
            .btn{
                border: 1px #3083ff solid;
                border-radius: 4px;
                background-color: #3487ff;
                box-shadow: 0 5px 8px 0 rgba(24,95,255,.1);
                color: #fff;
                text-align: center;
                font-weight: lighter;
                background-image: linear-gradient(0deg,#398bff,#3083ff);
                width: 60px;
                height: 40px;
                /* margin: 40px 0 8px; */
                font-size: 18px;
            }
            img{
                width: 45px;
                height: 45px;
            }
            .item-img{
                flex: 1 1 30%;
            }
            .commit{
                width: 350px;
                display: flex;
                justify-content: space-between;
                align-content: center;
            }
            a:link{
                text-decoration: none;
            }
        </style>
    </head>
    <body>
        <!-- vue-app的根容器 -->
        <div id="app" class="a">
            <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.image" />
                    </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" v-model="goods.count" class="goods-count"/>
                        <button type="button" @click="goods.count+=1">+</button>
                    </div>
                </div>
            </div>
            <hr/>
            <div class="commit">
                <p>总价：￥{{totalPrice}}</p>
                <button type="button" class="btn" @click="settl">结算</button>
            </div>
        </div>
        <script type="text/javascript">
            var app=new Vue({
                el:'#app',
                data:{
                    goodsList:[{
                        id:1,
                        name:'iPhone7',
                        price:5000,
                        count:1,
                        image:'img/iPhone7-2.jpg',
                        url:'https://item.jd.com/3133811.html'
                    },
                    {
                        id:2,
                        name:'iPhoneX',
                        price:7000,
                        count:2,
                        image:'img/iPhoneX.jpg',
                        url:'https://item.jd.com/5089253.html'
                    },
                    {
                        id:3,
                        name:'iPhone8',
                        price:6000,
                        count:1,
                        image:'img/iPhone8.jpg',
                        url:'https://item.jd.com/5089269.html'
                    }
                    ]
                },
                methods:{
                    settl:function(){
                        alert("您好，您本次购买手机"+this.totalCount+"部,共消费"+this.totalPrice+"元。");
                    }
                    },
                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;
                    },
                    totalCount: 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>

效果图：

day07-1.png

文章搜索

<html>
    <head>
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
        <title>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: 60%;
                margin: 0 auto;
            }

            .input-box {
                width: 50%;
                height: 25px;
                margin-bottom: 10px;
            }
            .btn{
                width: 50px;
                height: 25px;
                border: 1px #3083ff solid;
                border-radius: 4px;
                background-color: #3487ff;
                box-shadow: 0 5px 8px 0 rgba(24,95,255,.1);
                text-align: center;
                font-weight: lighter;
                background-image: linear-gradient(0deg,#398bff,#3083ff);
                font-size: 18px;
                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%;
            }
            a:link{
                color:#333333;
                text-decoration: none;
            }
        </style>
    </head>
    <body>
        <div id="app">
            <div class="container">
                <input type="text" v-model="searchString" placeholder="请输入" class="input-box" />
                <!-- <button type="button" class="btn" @click="filteredArticles">搜索</button> -->
                <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://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"
                        }
                    ]
                },
                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
                        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>

效果图：

day07-2.png

day07-3.png

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