[英]rewrite componentDidUpdate(prevProps) into a hook with redux
我想将此生命周期方法重写为一个钩子,但它没有按预期工作。 当组件didmount时,如果用户id存在于本地存储中,则用户已连接并且他的名字显示在导航栏中。 当他断开连接并重新连接时,他的名字会显示在导航栏中。 所以我试图用钩子转换这个类组件,当用户名改变时,导航栏中没有显示任何内容,所以我必须刷新页面,这样他的名字就会显示出来
真正的问题是 componentDidUpdate 我怎样才能得到和比较 prevProps 和钩子
类组件
const mapStateToProps = state => ({
...state.authReducer
}
);
const mapDispatchToProps = {
userSetId,
userProfilFetch,
userLogout
};
class App extends React.Component {
componentDidMount() {
const userId = window.localStorage.getItem("userId");
const {userSetId} = this.props;
if (userId) {
userSetId(userId)
}
}
componentDidUpdate(prevProps, prevState, snapshot) {
const {userId, userProfilFetch, userData} = this.props; //from redux store
if(prevProps.userId !== userId && userId !== null && userData === null){
userProfilFetch(userId);
}
}
render() {
return (
<div>
<Router>
<Routes/>
</Router>
</div>
);
}
}
export default connect(mapStateToProps,mapDispatchToProps)(App);
带挂钩
const App = (props) => {
const dispatch = useDispatch();
const userData = useSelector(state => state.authReducer[props.userData]);
const userId = window.localStorage.getItem("userId");
useEffect(()=> {
if(!userId){
dispatch(userSetId(userId))
dispatch(userProfilFetch(userId))
}
}, [userData, userId, dispatch])
return(
<Router>
<Routes/>
</Router>
)
};
export default App;
基本上创建一个自定义钩子来缓存一个值:
const usePrevious = value => {
const ref = useRef();
useEffect(() => {
ref.current = value;
});
return ref.current;
}
用法:
const App = (props) => {
const dispatch = useDispatch();
const userData = useSelector(state => state.authReducer[props.userData]);
const userId = window.localStorage.getItem("userId");
// get previous id and cache current id
const prevUserId = usePrevious(userId);
useEffect(()=> {
if(!userId){
dispatch(userSetId(userId))
dispatch(userProfileFetch(userId))
}
// do comparison with previous and current id value
if (prevUserId !== userId) {
dispatch(userProfileFetch(userId));
}
}, [userData, userId, prevUserId, dispatch])
return(
<Router>
<Routes/>
</Router>
)
};
仅供参考:您可能需要稍微重构一下代码,以便在仅在挂载时运行的效果挂钩中从本地存储中获取数据。 如果我正确理解您的应用程序流程,它将如下所示:
const App = (props) => {
const dispatch = useDispatch();
const { userId } = useSelector(state => state.authReducer[props.userData]);
useEffect(() => {
const userId = window.localStorage.getItem("userId");
userId && dispatch(userSetId(userId));
}, []);
// get previous id and cache current id
const prevUserId = usePrevious(userId);
useEffect(()=> {
if(!userId){
dispatch(userSetId(userId))
dispatch(userProfileFetch(userId))
}
// do comparison with previous and current id value
if (prevUserId !== userId) {
dispatch(userProfileFetch(userId));
}
}, [userId, prevUserId, dispatch])
return(
<Router>
<Routes/>
</Router>
)
};
现在我解决了,我做了这个
const App = props => {
const userId = window.localStorage.getItem("userId");
const dispatch = useDispatch();
const userData = useSelector(state=> state.authReducer[props.userData]);
const isAuthenticated = useSelector(state=> state.authReducer.isAuthenticated);
useEffect(()=> {
if(userId){
dispatch(userSetId(userId))
dispatch(userProfilFetch(userId))
}
}, [userId])
return(
<div>
<Router>
<Routes/>
</Router>
</div>
)
};
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