一个 Vuex 模块可以监视另一个 Vuex 模块吗？

Question

Vuex 模块可以监视其他模块的状态，并因此触发动作吗？

例如，让我们考虑以下情况：

store.js

import time from './store/time' ;
import position from './store/position' ;

const store = new Vuex.Store
(
    {
        modules:
        {
            time,
            position
        }    
    }
) ;

store/time.js

export default
{

    namespaced: true,

    state:
    {
        time: new Date()
    },

    getters:
    {
        time: (aState) => aState.time
    },

    mutations:
    {

        setTime (aState, aTime)
        {
            aState.time = aTime ;
        }

    }

} ;

store/position.js

export default
{

    namespaced: true,

    state:
    {
        positions: {}
    },

    getters:
    {
        positions: aState => aState.positions
    },

    mutations:
    {

        setPositions (aState, aPositionArray)
        {
            aState.positions = aPositionArray ;
        }

    },

    actions:
    {

        fetchPositionsAtTime ({ dispatch, commit, rootGetters }, { time })
        {
            // Fetch positions at given time from the server
            // commit('setPositions', ...)
        }

    }

} ;

理想情况下，我希望位置模块监视时间模块，并在时间状态更改后立即重新获取位置（即触发fetchPositionsAtTime）。

当然，我可以将调度添加到setTime 突变以触发位置模块操作，但我相信反过来（即观看）会更优雅（因为更多模块可能需要时间）。

有什么解决办法吗？ （当然不使用Vue Component，这就是重点）

Answer 1

您可以使用 store 实例的 watch 方法观察 time 状态，然后在 time 值更改时调度 fetchPositionsAtTime 操作：

store.watch((state) => state.time.time, (val) => {
  store.dispatch('position/fetchPositionsAtTime', { time: val })
});

如果您不想直接查看状态，也可以像这样查看 getter：

store.watch((state, getters) => getters['time/time'], (val) => {
  store.dispatch('position/fetchPositionsAtTime', { time: val })
});

Here's a link to the api documentation for Vuex.Store instances.

---

这是一个例子：

const time = {
  namespaced: true,
  state: {
    time: new Date()
  },
  getters: {
    time: (aState) => aState.time
  },
  mutations: {
    setTime (aState, aTime) {
      aState.time = aTime ;
    }
  }
};

const position = {
  namespaced: true,
  state: {
    positions: {}
  },
  getters: {
    positions: aState => aState.positions
  },
  mutations: {
    setPositions (aState, aPositionArray) {
      aState.positions = aPositionArray ;
    }
  },
  actions: {
    fetchPositionsAtTime ({ dispatch, commit, rootGetters }, { time }) {
      let value = rootGetters['position/positions'].value || 0;
      commit('setPositions', { value: ++value });
    }
  }
};

const store = new Vuex.Store({
  modules: { time, position }    
});

store.watch((state) => state.time.time, (val) => {
  store.dispatch('position/fetchPositionsAtTime', { time: val })
});

new Vue({
  el: '#app',
  store,
  methods: {
    setTime() {
      this.$store.commit('time/setTime', new Date());
    }
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vuex/3.0.1/vuex.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.16/vue.min.js"></script>

<div id="app">
  time: {{ $store.getters['time/time'] }}
  <br>
  position: {{ $store.getters['position/positions'] }}
  <br>
  <button @click="setTime">Change time</button>
</div>