- 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<!--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>{{test}}</p>
</div>
</template>
<script>
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]}
}
}
}
</script>
- 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>
{{$store.state.index.asyncData.items[0]}}可以取到改变的值,但是过程中还是出现这样的报错,原因同上
[Vue warn]: Error in render function: "TypeError: Cannot read property '0' of undefined"
所以这里的解决方法是:vuex结合computed、mapState或者合computed、mapGetters
parent.vue
<template>
<div>
父组件
<child></child>
</div>
</template>
<script>
import child from './child'
export default {
data: () => ({
}),
components: {
child
},
created () {
this.$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
<template>
<div>
子组件
<p>{{item0}}</p>
<p>{{item}}</p>
</div>
</template>
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>
这样是可以通过不报错的,就是created是空值,猜想上面vuex去stroe也可以也可以这样做
测试环境:vue v2.3.3, vue v2.3.1