Value passing problem of VUE2.0 components

##Transfer between Vue1.0 components

Use $on() to listen for events;

Use $emit() to trigger events on it;
Use $dispatch() to dispatch events, which bubble along the parent chain;
Use $broadcast() to broadcast events, and events are propagated downward to all descendants

After Vue2.0, $dispatch() and $broadcast() are deprecated, see https://cn.vuejs.org/v2/guide/migration.html#dispatch-and-broadcast-replacement

1. Pass the value from the child component to the parent component:

##Child.vue

<template>
  <p class="child">
    <h1>子组件</h1>
    <button v-on:click="childToParent">想父组件传值</button>
  </p>
</template>
<script>
  export default{
    name: 'child',
    data(){
      return {}
    },
    methods: {
      childToParent(){
        this.$emit("childToParentMsg", "子组件向父组件传值");
      }
    }
  }
</script>parent.vue

<template>
  <p class="parent">
    <h1>父组件</h1>
    <Child v-on:childToParentMsg="showChildToParentMsg" ></Child>
  </p>
</template>
<script>
  import Child from './child/Child.vue'
  export default{
      name:"parent",
    data(){
      return {
      }
    },
    methods: {
      showChildToParentMsg:function(data){
        alert("父组件显示信息："+data)
      }
    },
    components: {Child}
  }
</script>

2. Parent component passes value to child component

parent.vue

<template>
  <p class="parent">
    <h1>父组件</h1>
    <Child v-bind:parentToChild="parentMsg"></Child>
  </p>
</template>
<script>
  import Child from './child/Child.vue'
  export default{
     name:"parent",
    data(){
      return {
        parentMsg:'父组件向子组件传值'
      }
    },
    components: {Child}
  }
</script>

child.vue

<template>
  <p class="child">
    <h1>子组件</h1>
    <span>子组件显示信息：{{parentToChild}}</span><br>
  </p>
</template>
<script>
  export default{
    name: 'child',
    data(){
      return {}
    },
    props:["parentToChild"]
  }
</script>

3. Use eventBus.js to pass value ---Brother Value transfer between components

##eventBus.js

import Vue from 'Vue'
export default new Vue()

App.vue

<template>
  <p id="app">
    <secondChild></secondChild>
    <firstChild></firstChild>
  </p>
</template>

<script>
import FirstChild from &#39;./components/FirstChild&#39;
import SecondChild from &#39;./components/SecondChild&#39;

export default {
  name: &#39;app&#39;,
  components: {
    FirstChild,
    SecondChild,
  }
}
</script>

FirstChild.vue

<template>
  <p class="firstChild">
    <input type="text" placeholder="请输入文字" v-model="message">
    <button @click="showMessage">向组件传值</button>
    <br>
    <span>{{message}}</span>
  </p>
</template>
<script>
  import bus from &#39;../assets/eventBus&#39;;
  export default{
    name: &#39;firstChild&#39;,
    data () {
      return {
        message: &#39;你好&#39;
      }
    },
    methods: {
      showMessage () {
       alert(this.message)        bus.$emit(&#39;userDefinedEvent&#39;, this.message);//传值
      }
    }
  }
</script>

SecondChild.vue

<template>
    <p id="SecondChild">
        <h1>{{message}}</h1>
    </p>
</template>
<script>
    import bus from &#39;../assets/eventBus&#39;;
    export default{
        name:&#39;SecondChild&#39;,
        data(){
            return {
                message: &#39;&#39;
            }
        },
        mounted(){
            var self = this;            
            bus.$on(&#39;userDefinedEvent&#39;,function(message){                
            self.message = message;//接值            
            });
        }
    }

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