如何在 Vuex 2 中设置初始状态？

Question

我正在为一个小应用程序使用 Vue.js 2.0 和 Vuex 2.0。我正在通过调用从 API 检索初始状态的操作来初始化根 Vue 实例的 'created' 生命周期挂钩中的商店......就像在我的 中一样根组件：

const app = new Vue({
    el: "#app",
    router,
    store,
    data: {
        vacation: {},
    },
    components: {
        'vacation-status': VacationStatus,
    },
    created() {
        //initialize store data structure by submitting action.
        this.$store.dispatch('getVacation');
    },
    computed: {},
    methods: {}
});

这工作得很好。这是我在此处调用的对我商店的操作：

getVacation({ commit }) {
    api.getVacation().then(vacation => commit(UPDATE_VACATION, vacation))
}

这里是用'UPDATE_VACATION'进行的突变：

[UPDATE_VACATION] (state, payload) {
   state.vacation = payload.vacation;
},

我的问题： 当我加载应用程序时，我的所有组件都是 'getting' 来自商店的值，我试图访问 'undefined' 值在商店。也就是说state还没有初始化。

例如，我有一个组件在 子组件 中有吸气剂，如下所示：

computed: {
    arrival() {
        return this.$store.getters.arrival
    },
    departure() {
        return this.$store.getters.departure
    },
    countdown: function() {
        return this.$store.getters.countdown
    }
}

所有这些 getter 都会导致错误，因为 'vacation' 在状态对象上未定义。对我来说这似乎是一个异步问题，但可能是错误的。 我是否在错误的位置初始化我的商店状态？

Vue.use(Vuex);

export default new Vuex.Store({
    state: {},
    getters: {
        getVacation: state => {
            return state.vacation
        },
        guests: state => {
            return state.vacation.guests
        },
        verifiedGuests: state => {
            return state.vacation.guests.filter(guest => guest.verified)
        },
        emergencyContacts: state => {
            return state.emergency_contacts
        },
        arrival: state => {
            return state.vacation.check_in
        },
        departure: state => {
            return state.vacation.check_out
        },
        countdown: state => {
            let check_in = new Date(state.vacation.check_in);
            let now = new Date();

            if ((now - check_in) > 0) {
                return 'This vacation started on ' + check_in;
            }

            let difference = check_in - now;
            let day = 1000 * 60 * 60 * 24;

            return Math.ceil(difference / day) + " days until your vacation";
        }
    },
    mutations: {
        [UPDATE_VACATION](state, payload) {
            state.vacation = payload.vacation;
        },
        [ADD_GUEST](state, payload) {
            state.vacation.guests.push(payload.guest);
        },
        [REMOVE_GUEST](state, payload) {
            state.vacation.guests.filter(guest => {
                debugger;
                return guest.id != payload.guest.id
            })
        },
        [UPDATE_GUEST](state, payload) {
            state.vacation.guests.map(guest => {
                // Refactor Object.assign to deep cloning of object
                return guest.id === payload.guest.id ? Object.assign({}, guest, payload.guest) : guest;
            })
        },
        [ADD_EMERGENCY](state, payload) {
            state.vacation.emergency_contacts.push(payload.emergency_contact)
        },
        [REMOVE_EMERGENCY](state, payload) {
            state.vacation.emergency_contacts.filter(contact => contact.id !== payload.emergency_contact.id)
        },
        [UPDATE_EMERGENCY](state, payload) {
            state.vacation.emergency_contacts.map(contact => {
                // Refactor not needed because emergency_contact is a shallow object.
                return contact.id === payload.emergency_contact.id ? Object.assign({}, contact, payload.emergency_contact) : contact;
            });
        }
    },
    actions: {
        getVacation({
            commit
        }) {
            api.getVacation().then(vacation => commit(UPDATE_VACATION, vacation))
        },
        addGuest({
            commit
        }, guest) {
            commit(ADD_GUEST, guest);
        },
        removeGuest({
            commit
        }, guest) {
            commit(REMOVE_GUEST, guest);
        },
        updateGuest({
            commit
        }, guest) {
            commit(UPDATE_GUEST, guest);
        },
        addEmergency({
            commit
        }, guest) {
            commit(ADD_EMERGENCY, contact)
        },
        removeEmergency({
            commit
        }, contact) {
            commit(REMOVE_EMERGENCY, contact)
        },
        updateEmergency({
            commit
        }, contact) {
            commit(UPDATE_EMERGENCY, contact)
        },
        updateServer(store, payload) {
            return api.saveVacation(payload)
        }
    }
});

只是为了让其他人清楚解决方案：

我没有在商店中正确设置我的初始状态。我正在提取数据，并正确更新商店，但需要像这样初始化商店：

export default new Vuex.Store({
    state: {
        vacation: {} //I added this, and then justed updated this object on create of the root Vue Instance
    },
});

Answer 1

我认为你做的一切都是对的。也许您只是没有正确创建 getter（在您的代码中看不到任何定义）。或者您设置的初始状态不正确（在您的代码段中也不可见）。

我会使用 mapState 让状态属性在组件中可用。

在演示中，只需将 users 添加到 mapState 方法参数中的数组，用户数据将在组件中可用。（我刚刚添加了 getter users 来展示它是如何工作的。如果您使用的是 mapState，则不需要。）

请看下面的演示或这个fiddle。

const api =
  'https://jsonplaceholder.typicode.com/users'

const UPDATE_USERS = 'UPDATE_USERS'
const SET_LOADING = 'SET_LOADING'

const store = new Vuex.Store({
  state: {
    users: {},
    loading: false
  },
  mutations: {
    [UPDATE_USERS](state, users) {
      console.log('mutate users', users)
      state.users = users;
      console.log(state)
    }, [SET_LOADING](state, loading) {
      state.loading = loading;
    }
  },
  getters: {
    users(state) {
      return state.users
    }
  },
  actions: {
    getUsers({commit}) {
      commit(SET_LOADING, true);
      return fetchJsonp(api)
        .then((users) => users.json())
        .then((usersParsed) => {
          commit(UPDATE_USERS, usersParsed)
          commit(SET_LOADING, false)
        })
    }
  }
})

const mapState = Vuex.mapState;

const Users = {
  template: '<div><ul><li v-for="user in users">{{user.name}}</li></ul></div>',
  computed: mapState(['users'])
}

new Vue({
  el: '#app',
  store: store,
  computed: {
    ...mapState(['loading']),
      //...mapState(['users']),
      /*users () { // same as mapState
       return this.$store.state.users;
      }*/
      users() { // also possible with mapGetters(['users'])
        return this.$store.getters.users
      }
  },
  created() {
    this.$store.dispatch('getUsers')
  },
  components: {
    Users
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/fetch-jsonp/1.0.5/fetch-jsonp.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.1.10/vue.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vuex/2.1.1/vuex.min.js"></script>
<div id="app">
  <div v-if="loading">loading...</div>
  <users></users>
  <pre v-if="!loading">{{users}}</pre>
</div>

Answer 2

您可以创建一个 return 初始状态的函数，并将其用于您的 Vuex 实例，如下所示：

function initialStateFromLocalStorage() {
    ...
    const empty = {
        status: '',
        token: '',
        user: null
    }
    return empty;
}

export default new Vuex.Store({
    state: initialStateFromLocalStorage,
    ...

只要你 return 一个状态对象，你就可以在那个函数中做任何你想做的事，对吧？

如何在 Vuex 2 中设置初始状态？

How do I set initial state in Vuex 2?

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