Vuex基础-State

官方地址：https://vuex.vuejs.org/zh/guide/state.html

由于 Vuex 的状态存储是响应式的，从 store 实例中读取状态最简单的方法就是在计算属性中返回某个状态。

目录结构：

index.js:

import Vue from 'vue'
import Vuex from 'vuex'
import state from "./state"
import mutations from "./mutations"
import actions from "./actions"
import user from './module/user'

Vue.use(Vuex)

export default new Vuex.Store({
  state,
  mutations,
  actions,
  modules: {
    user
  }
})

state.js

const state = {
  appName:'admin'
}
export default state

user.js

const state = {
  //
  userName:'Caoqi'
}
const mutations = {
  //
}
const actions = {
  //
}
export default {
  state,
  mutations,
  actions
}

main.js

import Vue from 'vue'
import App from './App.vue'
import router from './router'
import store from './store'
import Bus from './lib/bus'

Vue.config.productionTip = false
Vue.prototype.$bus = Bus;

new Vue({
  router,
  store,
  render: h => h(App)
}).$mount('#app')

store.vue:

<template>
  <div>
    <a-input :value="inputValue" @input="handlerInput"></a-input>
    <p>appName: {{ appName }}</p>
    <p>userName : {{ userName }}</p>
  </div>
</template>
<script>
import AInput from "_c/AInput.vue";
import AShow from "_c/AShow.vue";

export default {
  name: "store",
  data() {
    return {
      inputValue: ""
    };
  },
  components: {
    AInput: AInput,
    AShow:AShow
  },
  computed:{
    appName () {
      return this.$store.state.appName
    },
    userName () {
      return this.$store.state.user.userName
    }
  },
  methods: {
    handlerInput(val) {
      this.inputValue = val;
    }
  }
};
</script>

效果：

根据官方说法：当一个组件需要获取多个状态时候，将这些状态都声明为计算属性会有些重复和冗余。为了解决这个问题，我们可以使用 mapState 辅助函数帮助我们生成计算属性，让你少按几次键：

上面的store.vue组件还可以这样写：

<template>
  <div>
    <a-input :value="inputValue" @input="handlerInput"></a-input>
    <p>appName: {{ appName }}</p>
    <p>userName : {{ userName }}</p>
  </div>
</template>
<script>
import AInput from "_c/AInput.vue";
import AShow from "_c/AShow.vue";
//变量的解构赋值，等同于import vuex from 'vuex'; const mapState=vuex.mapState;
import { mapState } from "vuex";
import { stat } from "fs";
export default {
  name: "store",
  data() {
    return {
      inputValue: ""
    };
  },
  components: {
    AInput: AInput,
    AShow: AShow
  },
  computed: {
    //ES6展开操作符 mapState展开会形成一个对象 使用对象展开运算符将此对象混入到外部对象中
    ...mapState({
      appName: state => state.appName,
      userName: state => state.user.userName
    })
  },
  methods: {
    handlerInput(val) {
      this.inputValue = val;
    }
  }
};
</script>

如果在模块中使用了命名空间，如在user.js中使用了命名空间：

const state = {
  //
  userName:'Caoqi'
}
const mutations = {
  //
}
const actions = {
  //
}
export default {
  namespaced:true,//有利于模块更加密闭，不受外界的干扰
  state,
  mutations,
  actions
}

则需要修改store.vue组件代码：

<template>
  <div>
    <a-input :value="inputValue" @input="handlerInput"></a-input>
    <p>appName: {{ appName }}</p>
    <p>userName : {{ userName }}</p>
  </div>
</template>
<script>
import AInput from "_c/AInput.vue";
import AShow from "_c/AShow.vue";
//变量的解构赋值，等同于import vuex from 'vuex'; const mapState=vuex.mapState;
import { mapState } from "vuex";
import { stat } from "fs";
export default {
  name: "store",
  data() {
    return {
      inputValue: ""
    };
  },
  components: {
    AInput: AInput,
    AShow: AShow
  },
  computed: {
    ...mapState({
      appName: state => state.appName
    }),
    ...mapState('user',{
      userName: state => state.userName
    })
  },
  methods: {
    handlerInput(val) {
      this.inputValue = val;
    }
  }
};
</script>