State在状态改变后不触发重新渲染

Question

我在我的React应用程序中结合了两个reducer。其中一个工作正常，但一个在状态发生变化后不触发重新渲染。但是当我保存文档或更改其他减速器状态后，两个减速器的组件都会重新渲染

减速机不能正常工作:

import {
SET_ACTIVE_SUBJECT,
SET_ACTIVE_TOPIC
} from '../action/action-types'
const initialState = {
activeSubject: '',
activeTopic: ''
}
const makeState = (stateActiveSubject, stateActiveTopic) => {
return {
activeSubject: stateActiveSubject,
activeTopic: stateActiveTopic
}
}

export const uireducer = (state = initialState, action) => { 
switch(action.type){
case SET_ACTIVE_SUBJECT:
// this statement is printing new state in console, but not triggering re-render
console.log('New State : ', makeState(action.payload,''));  
return makeState(action.payload,'')
case SET_ACTIVE_TOPIC:
return makeState(state.uireducer.activeSubject,action.payload)
default:
return state
}
}

不重新渲染的组件:

const Topics = ({activeSubject, data}) => {
const classes = useStyles()
const [topics, setTopics] = useState([])
useEffect(() => {
console.log('Active Subject : ', activeSubject);
if(activeSubject){
console.log('Data : ', data.filter(subject => (subject.id === activeSubject))[0].topics);
setTopics(data.filter(subject => (subject.id === activeSubject))[0].topics)
}
}, [])
return (
<List>
{
topics.length > 0 ? topics.map(topic => {
return (
<ListItem button className={classes.listItem} id={topic.id} key={topic.id}>
{topic.name}
<ButtonGroup className={classes.editDelete}>
<IconButton className={classes.icon}>
<Edit />
</IconButton>
<IconButton className={classes.icon}>
<Delete />
</IconButton>
</ButtonGroup>
</ListItem>
)
}) : <div className={classes.waitMessage}><p>Select Subject To Display Topics</p></div>
}
</List>
)
}
const mapStateToProps = state => ({
activeSubject: state.uireducer.activeSubject,
data: state.subjects.data
})
const mapDispatchToProps = dispatch => ({
})
export default connect(mapStateToProps, mapDispatchToProps)(Topics);  

工作正常的减速机:

import {
FETCHING_DATA,
FETCHED_DATA,
FETCH_DATA_ERROR
} from '../action/action-types'
const initialState = {
isDataFetching : false,
error: '',
data: [],
}
const makeState = (dataFetching, stateError, stateData) =>  {
return {
isDataFetching: dataFetching,
error: stateError,
data: stateData,
}
}
export const reducer = (state = initialState, action) => {
switch(action.type){
case FETCHING_DATA:
return makeState(true,'',[])
case FETCHED_DATA:
return makeState(false,'',action.payload)
case FETCH_DATA_ERROR:
return makeState(false,action.payload,[])
default:
return state
}
}

存储在这里:

import { createStore, combineReducers, applyMiddleware } from 'redux'
import thunk from 'redux-thunk';
import {reducer}  from '../reducer/reducer'
import { uireducer } from '../reducer/uireducer'
console.log(reducer);
const rootReducer = combineReducers({
subjects: reducer,
uireducer
})
const store = createStore(rootReducer, applyMiddleware(thunk))
export default store

Answer 1

将activeSubject设置为useEffect的依赖项，因此当值更改时它将重新运行。

useEffect(() => {
// ...
}, [activeSubject])