vuex如何修改状态state的方法

const state = {
  num:0
}
const mutations = {
  SET_NUM(state, payload) {
    state.num= payload;
  },
}
export default new Vuex.Store({
  state,
  mutations
})

<template>
  ...
</template>
<script>
  export default{
    data(){
      return{
        num:1
      }
    },
    methods:{
	  doSomething(){
	    this.$store.commit('SET_NUM',this.num);
	  }	
	}
  }
</script>

 doSomething(){
   this.$store.state.num = this.num;
 }	

// 在JS中使用
this.$store.state.变量名        // 不分模块
this.$store.state.模块名.变量名 // 分模块//在模板上使用
$store.state.变量名        // 不分模块
$store.state.模块名.变量名 // 分模块

import { mapState } from 'vuex'
export default {
    computed: {
        ...mapState(['state属性名'])              // 不分模块，不修改属性名
        ...mapState({'新属性名称':'state属性名'}) // 不分模块，修改属性名
        ...mapState('模块名', ['state属性名'])    // 分模块，不修改属性名
    }
}

import Vue from 'vue';
import Vuex from 'vuex';Vue.use(Vuex);
const counterStore = new Vuex.Store(
    {
        state: {
            count: 10
        },
    }
);export default counterStore;

<template>
  <div class="outer">
    <h3>父组件</h3>
    <component-b></component-b>
  </div>
</template><script>
import ComponentB from "./ComponentB";export default {
  name: 'Parent',
  components: {ComponentB},
}
</script><style scoped>
.outer {
  margin: 20px;
  border: 2px solid red;
  padding: 20px;
}
</style>

<template>
  <div class="container">
    <h3>ComponentB</h3>
    计数器的值：{{thisCount}}
    <!--也可以这么写：-->
    <!--计数器的值：{{this.$store.state.count}}-->
  </div>
</template><script>
export default {
  computed:{
    thisCount() {
      return this.$store.state.count;
    }
  }
}
</script><style scoped>
.container {
  margin: 20px;
  border: 2px solid blue;
  padding: 20px;
}
</style>

import Vue from 'vue'
import Router from 'vue-router'
import Parent from "../components/Parent";Vue.use(Router)export default new Router({
  routes: [
    {
      path: '/parent',
      name: 'Parent',
      component: Parent,
    }
  ],
})