Detailed explanation of the operation of $emit and $on parent-child sibling components in vue-JS Tutorial-php.cn

This time I will bring you a detailed explanation of the operation of $emit and $on parent-child and brother components in vue. What are the precautions for the operation of $emit and $on parent-child and brother components in vue. The following is a practical case. Let’s take a look.

There are three main transmission methods:

1. Communication from parent component to child component

2. Communication from child component to parent component

3. Communication between sibling components

1. Parent component passes value to child component

Parent component passes values to child component using props

//父组件：parent.vue
<template>
  <p>
    <child :vals = "msg"></child>
  </p>
</template>
<script>
import child from "./child";
export default {
  data(){
    return {
      msg:"我是父组件的数据，将传给子组件"
    }
  },
  components:{
    child
  }
}
</script>
//子组件：child.vue
<template>
  <p>
    {{vals}}
  </p>
</template>
<script>
export default {
   props:{ //父组件传值 可以是一个数组，对象
    vals:{
      type:String,//类型为字符窜
     default:"123" //可以设置默认值
    }
  },
}
</script>

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2. Communication from child component to parent component

Use $emit(eventname,option) Trigger event,

Parameter 1: Customize the event name, written in lowercase or connected with -, such as event, event-name cannot be written in camel case (eventName)

The sub-component passes the value to the parent component and can be used in the sub-component The value of the event triggered by $emit is passed out, and the parent component obtains the data through event monitoring.

However, there is a problem here.

1. It is the child component that actively transmits data to the parent component. The parent component listens and receives (it is determined by the operation in the child component when to pass the value)

2. Or it is the parent component that determines when the child component passes the value to the parent component, and then listens and receives (it is determined by the operation in the parent component) When to pass the value)

Both cases exist

2.1: $meit event trigger, customized through event trigger inside sub-component Event $emit

2.2: The $meit event is triggered. The custom event $emit

can be triggered by the event of the parent component operating the child component (ref). The first case:

//父组件：parent.vue
<template>
  <p>
    <child v-on:childevent=&#39;wathChildEvent&#39;></child>
    <p>子组件的数据为：{{msg}}</p>
  </p>
</template>
<script>
import child from "./child";
export default {
  data(){
    return{
      msg:""
    }
  },
  components:{
    child
  },
  methods:{
    wathChildEvent:function(vals){//直接监听 又子组件触发的事件，参数为子组件的传来的数据
      console.log(vals);//结果：这是子组件的数据，将有子组件操作触发传给父组件
      this.msg = vlas;
    } 
  }
}
</script>
//子组件：child.vue
<template>
  <p>
    <input type="button" value="子组件触发" @click="target">
  </p>
</template>
<script>
export default {
  data(){
      return {
      texts:'这是子组件的数据，将有子组件操作触发传给父组件'
      }
  },
  methods:{
    target:function(){ //有子组件的事件触发 自定义事件childevent
      this.$emit('childevent',this.texts);//触发一个在子组件中声明的事件 childEvnet
    }
  },
}
</script>

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Second case:

//父组件：parent.vue
<template>
  <p>
    <child v-on:childevent=&#39;wathChildEvent&#39; ref="childcomp"></child>
    <input type="button" @click="parentEnvet" value="父组件触发" />
    <p>子组件的数据为：{{msg}}</p>
  </p>
</template>
<script>
import child from "./child";
export default {
  data(){
    return{
      msg:""
    }
  },
  components:{
    child
  },
  methods:{
    wathChildEvent:function(vals){//直接监听 又子组件触发的事件，参数为子组件的传来的数据
      console.log(vals);//这是子组件的数据，将有子组件操作触发传给父组件
      this.msg = vlas;
    },
    parentEnvet:function(){
      this.$refs['childcomp'].target(); //通过refs属性获取子组件实例，又父组件操作子组件的方法触发事件$meit
    }
  }
}
</script>
//子组件：child.vue
<template>
  <p>
   <!-- dothing..... -->
  </p>
</template>
<script>
export default {
  data(){
      return {
      texts:'这是子组件的数据，将有子组件操作触发传给父组件'
      }
  },
  methods:{
    target:function(){ //又子组件的事件触发 自定义事件childevent
      this.$emit('childevent',this.texts);//触发一个在子组件中声明的事件 childEvnet
    }
  },
}
</script>

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Comparing the two situations, the difference lies in whether the $emit custom event is triggered by a parent component or a child component To trigger

The first way is to define a click event in the child component to trigger the custom event $emit, and then listen to it in the parent component

The second way is to use it in the parent component For the first click event, obtain the instance method through refs in the component to directly trigger the event, and then listen in the parent component

3. Communication between sibling components

(1) , Transfer data between brothers through events

(2) Create a new Vue instance so that each brother shares the same event mechanism. (Key points)

(3) When passing data, $emit (method name, passed data) is triggered through events.

(4) The data receiving party triggers the event $on (method name, callback (received data)) in the mounted() hook function (mounted instance). At this time, this in the callback function Changes have been made to use arrow functions.

//建立一个空的Vue实例,将通信事件挂载在该实例上
//emptyVue.js
import Vue from 'vue'
export default new Vue()
//兄弟组件a:childa.vue
<template>
  <p>
    <span>A组件->{{msg}}</span>
    <input type="button" value="把a组件数据传给b" @click ="send">
  </p>
</template>
<script>
import vmson from "./emptyVue"
export default {
  data(){
    return {
      msg:"我是a组件的数据"
    }
  },
  methods:{
    send:function(){
      vmson.$emit("aevent",this.msg)
    }
  }
}
</script>
//兄弟组件b:childb.vue
<template>
   <p>
    <span>b组件,a传的的数据为->{{msg}}</span>
  </p>
</template>
<script>
import vmson from "./emptyVue"
export default {
 data(){
    return {
      msg:""
    }
  },
  mounted(){
    vmson.$on("aevent",(val)=>{//监听事件aevent，回调函数要使用箭头函数;
      console.log(val);//打印结果：我是a组件的数据
      this.msg = val;
    })
  }
}
</script>
//父组件：parent.vue
<template>
  <p>
    <childa><childa>
    <childb></childb>
  </p>
</template>
<script>
import childa from "./childa";
import childb from "./childb";
export default {
  data(){
    return{
      msg:""
    }
  },
  components:{
    childa,
    childb
  },
}
</script>

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I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!