Vue 计算的属性不响应状态更改

Question

我无法弄清楚为什么调用fetch()方法时以下组件中的details计算属性没有更新：

<template>
<div>
{{ haveData }} //remains undefined
</div>
</template>
<script>
export default {
props: {
group: {
type: Object,
required: true
},
},
computed: {
currentGroup() {
return this.$store.getters['user/navbar_menu_app_current_group'](
this.group.id
)
/*-- which is the following function 
navbar_menu_app_current_group: state => item => {
return state.menu.find(m => {
return m.id == item
})
}
*/
/*-- this function returns an object like so 
{
id: 1,
label: 'kity cats',
}
***details --> IS NOT DEFINED. If I add it to the current group as null, my problem goes away. However, this is a previous API call that does not set the `details` parameter.
*/
},
details() {
let c = this.currentGroup.details
console.log(c) // returns undefined, which makes sense, but it should be updated after this.fetch() is called
return c
},
haveData() {
return this.details != null
}
},
methods: {
async fetch() {
await this.$store.dispatch(
'user/navbar_menu_app_details_get',
this.group.id
)
//This is setting the "details" part of the state on menu which is referred to in the computed properties above
//Previous to this there is no state "this.group.details"
//If I add a console log to the mutation the action calls, I get what is expected.
}
},
created() {
if (!this.haveData) {
this.fetch()
}
}
}
</script>

如果我更改数组项目以包含details，它可以工作：

{
id: 1,
label: 'kity cats',
details: null  // <-- added
}

不幸的是，数组是从大型 API 调用创建的，添加details似乎没有必要，因为它可能永远不需要。

如何在不将details:null添加到默认状态的情况下使计算属性正常工作？

尝试 1：

// Vuex mutation
navbar_menu_app_details_set(state, vals) {
let app = state.menu.find(item => {
return item.id == vals[0] //-> The group id passing in the dispatch function 
})
//option 1 = doesn't work
app = { app, details: vals[1] } //-> vals[1] = the details fetched from the action (dispatch)
//option 2 = doesnt work
app.details = vals[1]
//option 3 = working but want to avoid using Vue.set()
import Vue from 'vue' //Done outside the actual function
Vue.set( app, 'details', vals[1])
},

尝试 2：

// Vuex action
navbar_menu_app_details_get(context, id) {
return new Promise((resolve, reject) => {
setTimeout(() => {
context.commit('navbar_menu_app_details_set', [
context.getters.navbar_menu_app_current(id), //-> the same as find function in the mutation above
apps[id]
])
resolve()
}, 1000)
})
}
// --> mutation doesn't work
navbar_menu_app_details_set(state, vals) {
vals[0].details = vals[1]
},

Answer 1

Vue 实例可以通过this._vm从 Vuex 突变中获得，您可以使用vm.$set()(相当于Vue.set()(将details添加到菜单项中：

navbar_menu_app_details_set(state, vals) {
let app = state.menu.find(item => {
return item.id == vals[0]
})
this._vm.$set(app, 'details', vals[1])
},

Answer 2

Vue中的所有对象都是反应式的，并且设计的方式是，只有当重新分配对象时，才会捕获更改并发生更改检测。

这样，在您的情况下，以下应该可以正常工作。

app = { ...app, details: vals[1] }