VUE框架 子组件传递数据给父组件/父组件向子组件传递数据

<template>
  <div>
    <ul>
      <li v-for="menu in menu_list"><a :href="menu.link">{{ menu.name }}</a></li>
      <li>
        &nbsp;&nbsp;&nbsp; <span>所在地：</span><select v-model="city" name="" id="">
        <option value="北京">北京</option>
        <option value="上海">上海</option>
        <option value="深圳">深圳</option>
      </select>
      </li>
    </ul>

  </div>
</template>

<script>
export default {
  name: "Nav",
  data() {
    return {
      menu_list: [
        {name: "百度", "link": "http://www.baidu.com"},
        {name: "腾讯", "link": "http://www.qq.com"},
        {name: "小米", "link": "http://www.xiaomi.com"},
      ],
     city:"北京",
    }
  },
  created(){
    this.$emit("getCity", this.city);
  },
  watch:{
    city(newVal,oldVal){
        console.log(newVal,oldVal)
        this.$emit("getCity", newVal);
    }
  },

}
</script>

<style scoped>
ul, li {
  list-style: none;
  padding: 0;
  margin: 0;
}

ul::after {
  overflow: hidden;
  clear: both;
  display: block;
  content: "";
}

li {
  float: left;
  margin: 0 20px;
}

a {
  text-decoration: none;
  color: #666;
}
</style>

<template>
    <h1>天气预报</h1>
    <p> <input type="text" placeholder="请输入查询城市" v-model="choose_city">
        <button @click="sendAjax">查询</button>
    </p>
    <div>{{forecast}}</div>

    <table border="1" v-if="forecasts.length>1">
        <tr>
            <td>日期</td>
            <td>类型</td>
            <td>最高气温</td>
            <td>最低气温</td>
            <td>风向</td>
        </tr>

        <tr v-for="day_forecast in forecasts">
            <td>{{day_forecast.date}}</td>
            <td>{{day_forecast.type}}</td>
            <td>{{day_forecast.high}}</td>
            <td>{{day_forecast.low}}</td>
            <td>{{day_forecast.fengxiang}}</td>
        </tr>
    </table>
</template>

<script>
import axios from "axios";
export default {
  name: "Forecast",
  data(){
    return{
        forecasts: [],
    }
  },
          methods: {
            sendAjax(){
                var that = this;
                axios.get("http://wthrcdn.etouch.cn/weather_mini",{
                    params: {
                        city: that.choose_city,
                    }
                }).then(function (response) {
                    console.log("response",response);
                    that.forecasts = response.data.data.forecast
                })
            }
        },
        created(){
            this.sendAjax()
        },
        watch:{
            choose_city(newVal,oldVal){
                this.sendAjax()
            }
        },
        props: {
            choose_city: {
                default: "北京",
                type: String,
            }
        },
  }
</script>

<style scoped>
        tr td{
            padding: 10px;
             100px;
        }
        table{
            margin: 0 auto;
        }
</style>

<template>
  <div class="home">
  <Nav @getCity="callBack"></Nav>
  <p>选中的城市:北京</p>
  <Forecast :choose_city="city"></Forecast>


  </div>
</template>

<script>
// @ is an alias to /src
import Nav from '@/components/Nav.vue'
import Forecast from '@/components/Forecast.vue'
export default {
  name: 'HomeView',
  components: {
    Nav,
    Forecast,

  },
  methods: {
    callBack(choose_city){
        this.city = choose_city
    },
  }
}
</script>