vue解决组件传值异步问题

转载自：http://www.jb51.net/article/117447.htm案例一父组件parent.vue// asyncData为异步获取的数据，想传递给子组件使用<template><div>父组件<child :child-data="asyncData"></ch

Crying_cat

13016人浏览 · 2018-04-28 14:18:23

Crying_cat · 2018-04-28 14:18:23 发布

转载自：http://www.jb51.net/article/117447.htm
案例一

父组件parent.vue

// asyncData为异步获取的数据，想传递给子组件使用
<template>
 <div>
  父组件
  <child :child-data="asyncData"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncData: ''
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncData = 'async data'
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

子组件child.vue

<template>
 <div>
  子组件{{childData}}
 </div>
</template>

<script>
 export default {
  props: ['childData'],
  data: () => ({
  }),
  created () {
   console.log(this.childData) // 空值
  },
  methods: {
  }
 }
</script>

上面按照这里的解析，子组件的html中的{{childData}}的值会随着父组件的值而改变，但是created里面的却不会发生改变(生命周期问题)

案例二
parent.vue

<template>
 <div>
  父组件
  <child :child-object="asyncObject"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncObject: ''
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncObject = {'items': [1, 2, 3]}
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>
  子组件<!--这里很常见的一个问题，就是{{childObject}}可以获取且没有报错，但是{{childObject.items[0]}}不行，往往有个疑问为什么前面获取到值，后面获取不到呢？-->
  <p>{{childObject.items[0]}}</p>
 </div>
</template>

<script>
 export default {
  props: ['childObject'],
  data: () => ({
  }),
  created () {
   console.log(this.childObject) // 空值
  },
  methods: {
  }
 }
</script>

created里面的却不会发生改变，子组件的html中的{{{childObject.items[0]}}的值虽然会随着父组件的值而改变，但是过程中会报错

// 首先传过来的是空，然后在异步刷新值，也开始时候childObject.items[0]等同于”.item[0]这样的操作，所以就会报下面的错

vue.esm.js?8910:434 [Vue warn]: Error in render function: "TypeError: Cannot read property '0' of undefined"

针对二的解决方法：

使用v-if可以解决报错问题，和created为空问题

// parent.vue
<template>
 <div>
  父组件
  <child :child-object="asyncObject" v-if="flag"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncObject: '',
   flag: false
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncObject = {'items': [1, 2, 3]}
    this.flag = true
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>
  子组件
  <!--不报错-->
  <p>{{childObject.items[0]}}</p>
 </div>
</template>

<script>
 export default {
  props: ['childObject'],
  data: () => ({
  }),
  created () {
   console.log(this.childObject)// Object {items: [1,2,3]}
  },
  methods: {
  }
 }
</script>

子组件使用watch来监听父组件改变的prop，使用methods来代替created
parent.vue

template>
 <div>
  父组件
  <child :child-object="asyncObject"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncObject: ''
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncObject = {'items': [1, 2, 3]}
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>
  子组件<!--1-->
  <p>{{test}}</p>
 </div>
</template>

<script>
 export default {
  props: ['childObject'],
  data: () => ({
   test: ''
  }),
  watch: {
   'childObject.items': function (n, o) {
    this.test = n[0]
    this.updata()
   }
  },
  methods: {
   updata () { // 既然created只会执行一次，但是又想监听改变的值做其他事情的话，只能搬到这里咯
    console.log(this.test)// 1
   }
  }
 }
</script>

子组件watch computed data 相结合，有点麻烦
parent.vue

<template>
 <div>
  父组件
  <child :child-object="asyncObject"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncObject: undefined
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncObject = {'items': [1, 2, 3]}
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>

子组件
*

export default { props: ['childObject'], data: () => ({ test: '' }), watch: { 'childObject.items': function (n, o) { this._test = n[0] } }, computed: { _test: { set (value) { this.update() this.test = value }, get () { return this.test } } }, methods: { update () { console.log(this.childObject) // {items: [1,2,3]} } } } * 使用emit，on，bus相结合 parent.vue

<template>
 <div>
  父组件
  <child></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
  }),
  components: {
   child
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    // 触发子组件，并且传递数据过去
    this.$bus.emit('triggerChild', {'items': [1, 2, 3]})
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>
  子组件
  <p>{{test}}</p>
 </div>
</template>

<script>
 export default {
  props: ['childObject'],
  data: () => ({
   test: ''
  }),
  created () {
   // 绑定
   this.$bus.on('triggerChild', (parmas) => {
    this.test = parmas.items[0] // 1
    this.updata()
   })
  },
  methods: {
   updata () {
    console.log(this.test) // 1
   }
  }
 }
</script>

这里使用了bus这个库，parent.vue和child.vue必须公用一个事件总线（也就是要引入同一个js，这个js定义了一个类似let bus = new Vue()的东西供这两个组件连接），才能相互触发

使用prop default来解决{{childObject.items[0]}}
parent.vue

<template>
 <div>
  父组件
  <child :child-object="asyncObject"></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
   asyncObject: undefined // 这里使用null反而报0的错
  }),
  components: {
   child
  },
  created () {
  },
  mounted () {
   // setTimeout模拟异步数据
   setTimeout(() => {
    this.asyncObject = {'items': [1, 2, 3]}
    console.log('parent finish')
   }, 2000)
  }
 }
</script>

child.vue

<template>
 <div>
  子组件<!--1-->
  <p>{{childObject.items[0]}}</p>
 </div>
</template>

<script>
 export default {
  props: {
   childObject: {
    type: Object,
    default () {
     return {
      items: ''
     }
    }
   }
  },
  data: () => ({
  }),
  created () {
   console.log(this.childObject) // {item: ''}
  }
 }
</script>

在说用vuex解决方法的时候，首先看看案例三

案例三
main.js

import Vue from 'vue'
import App from './App'
import router from './router'
import VueBus from 'vue-bus'
import index from './index.js'
Vue.use(VueBus)

Vue.config.productionTip = false
import Vuex from 'vuex'
Vue.use(Vuex)
const store = new Vuex.Store({
 modules: {
  index
 }
})
/* eslint-disable no-new */
new Vue({
 el: '#app',
 store,
 router,
 template: '<App/>',
 components: { App }
})

index.js

const state = {
 asyncData: ''
}

const actions = {
 asyncAction ({ commit }) {
  setTimeout(() => {
   commit('asyncMutation')
  }, 2000)
 }
}
const getters = {
}

const mutations = {
 asyncMutation (state) {
  state.asyncData = {'items': [1, 2, 3]}
 }
}

export default {
 state,
 actions,
 getters,
 mutations
}

parent.vue

<template>
 <div>
  父组件
  <child></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
  }),
  components: {
   child
  },
  created () {
   this.$store.dispatch('asyncAction')
  },
  mounted () {
  }
 }
</script>

child.vue

<template>
 <div>
  子组件
  <p>{{$store.state.index.asyncData.items[0]}}</p>
 </div>
</template>

<script>
 export default {
  data: () => ({
  }),
  created () {
  },
  methods: {
  }
 }
</script>

{{$store.state.index.asyncData.items[0]}}可以取到改变的值，但是过程中还是出现这样的报错，原因同上

复制代码代码如下:

[Vue warn]: Error in render function: “TypeError: Cannot read property ‘0’ of undefined”

所以这里的解决方法是：vuex结合computed、mapState或者合computed、mapGetters

parent.vue

<template>
 <div>
  父组件
  <child></child>
 </div>
</template>

<script>
 import child from './child'
 export default {
  data: () => ({
  }),
  components: {
   child
  },
  created () {
   this.$store.dispatch('asyncAction')
  },
  mounted () {
  }
 }
</script>

child.vue

<template>
 <div>
  子组件
  <p>{{item0}}</p>
  <p>{{item}}</p>
 </div>
</template>

<script>
 import { mapState, mapGetters } from 'vuex'
 export default {
  data: () => ({
   test: ''
  }),
  computed: {
   ...mapGetters({
    item: 'getAsyncData'
   }),
   ...mapState({
    item0: state => state.index.asyncData
   })
  },
  created () {
  },
  methods: {
  }
 }
</script>

index.js

const state = {
 asyncData: ''
}

const actions = {
 asyncAction ({ commit }) {
  setTimeout(() => {
   commit('asyncMutation', {'items': [1, 2, 3]})// 作为参数，去调用mutations中的asyncMutation方法来对state改变
  }, 2000)
 }
}
const getters = {
 getAsyncData: state => state.asyncData
}

const mutations = {
 asyncMutation (state, params) {
  state.asyncData = params.items[0] // 此时params={'items': [1, 2, 3]}被传过来赋值给asyncData，来同步更新asyncData的值，这样html就可以拿到asyncData.items[0]这样的值了
 }
}

export default {
 state,
 actions,
 getters,
 mutations
}

注意上面的

….
commit(‘asyncMutation’, {‘items’: [1, 2, 3]})
…
state.asyncData = params.items[0]
如果写成这样的话

commit(‘asyncMutation’)
state.asyncData = {‘items’: [1, 2, 3]}
首先asyncAction是个异步的操作，所以asyncData默认值为空，那么还是导致,child.vue这里报0的错

子组件

不过根据以上的案例，得出来一个问题就是异步更新值的问题，就是说开始的时候有个默认值，这个默认值会被异步数据改变，比如说这个异步数据返回的object，如果你用props的方式去传递这个数据，其实第一次传递的空值，第二次传递的是更新后的值，所以就出现{{childObject.items[0]}}类似这种取不到值的问题，既然说第一次是空值，它会这样处理”.items[0],那么我们是不是可以在html判断这个是不是空（或者在computed来判断是否为默认值），所以把案例二的child.vue

<template>
 <div>
  <p>{{childObject != '' ? childObject.items[0]: ''}}</p>
 </div>
</template>

<script>
 export default {
  props: ['childObject'],
  data: () => ({
  }),
  created () {
   console.log(this.childObject) // 空值
  },
  methods: {
  }
 }
</script>

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