为什么我开始做出反应,我尝试使用cookie从api中获取用户数据,所以我有数据,但是当我console.log()用户数据时,我有4个未定义,然后有2个相同的对象数据。问题是我不知道为什么以及何时尝试使用道具在其他组件中获取user.id时,我的tpyerror id未定义。
import React, {useState, useEffect} from "react";
import NavBar from "./component/NavBar";
import Navigation from "./component/Navigation"
import Cookie from "js-cookie"
import axios from "axios"
import "./App.css";
function App() {
const [user, setUser] = useState()
const [logged, setLogged] = useState(false)
const cookie = Cookie.get("login")
useEffect(() => {
axios.post('/getdatafromcookie', cookie)
.then((res) => {
if(res.data.success === true){
setLogged(true)
setUser(res.data.user)
}
})
}, [])
console.log(user)
return (
<div className="App">
<header className="NavHeader">
<NavBar user={user} logged={logged} />
</header>
<Navigation user={user} logged={logged}/>
</div>
);
}
export default App;
控制台日志显示我:
导航栏
import React, { useState, useEffect } from "react";
import RegisterForm from "../component/RegisterForm";
import RegisterLogin from "../component/RegisterLogin";
import { Navbar, Nav, Dropdown } from "react-bootstrap";
import { Button } from "@material-ui/core"
export default function NavBar(props) {
const [modalLoginShow, setModalLoginShow] = useState();
const [modalRegisterShow, setModalRegisterShow] = useState();
const user = props.user
const islogged = props.logged
if(islogged === false)
{
return (
<Navbar collapseOnSelect expand="lg" bg="transparent" variant="light">
<Navbar.Brand href="/">Matchandate</Navbar.Brand>
<Navbar.Toggle aria-controls="responsive-navbar-nav" />
<Navbar.Collapse id="responsive-navbar-nav">
<Nav className="mr-auto"></Nav>
<Nav>
<Nav.Link onClick={() => setModalLoginShow(true)}>
<Button variant="contained" color="secondary">Login</Button>
</Nav.Link>
<Nav.Link onClick={() => setModalRegisterShow(true)}>
<Button variant="contained" color="secondary" >Register</Button>
</Nav.Link>
</Nav>
</Navbar.Collapse>
<RegisterLogin show={modalLoginShow} onHide={() => setModalLoginShow(false)} />
<RegisterForm show={modalRegisterShow} onHide={() => setModalRegisterShow(false)} />
</Navbar>
)
}
return(
<Navbar collapseOnSelect expand="lg" bg="transparent" variant="light">
<Navbar.Brand href="/">Matchandate</Navbar.Brand>
<Navbar.Toggle aria-controls="responsive-navbar-nav" />
<Navbar.Collapse id="responsive-navbar-nav">
<Nav className="mr-auto"></Nav>
<Nav>
<Nav.Link href="/profile">
<Button variant="contained" color="primary">Profile</Button>
</Nav.Link>
<Nav.Link href="/logout">
<Button variant="contained" color="primary" >Logout</Button>
</Nav.Link>
</Nav>
</Navbar.Collapse>
</Navbar>
)
}
导航
import React from "react"
import Slider from "./SliderHome";
import Activate from "./Activate";
import ForgotPwd from "./Pages/ForgotPwd"
import ChangePwd from "./Pages/ChangePwd"
import UserProfile from "./Pages/UserProfil";
import ErrorPage from "./Pages/ErrorPage"
import { BrowserRouter as Router, Route, Switch, Redirect } from "react-router-dom";
export default function Navigation(props){
const user = props.user
const islogged = props.logged
if(islogged){
return(
<Router>
<Switch>
<Route exact path="/" exact component={Slider} />
<Route exact path="/profile" component={() => <UserProfile user={user} />} />
{/* <Route path="/user/:id" component={ChangePwd}/> */}
<Route path="/" component={ErrorPage} />
</Switch>
</Router>
)
}
return (
<Router>
<Switch>
<Route exact path="/" exact component={Slider} />
<Route path="/activate" component={Activate} />
<Route path="/forgot-pwd" component={ForgotPwd}/>
<Route path="/changepwd" component={ChangePwd}/>
{/* <Route path="/user/:id" component={ChangePwd}/> */}
<Route path="/" component={ErrorPage} />
</Switch>
</Router>
)
}
答案 0 :(得分:0)
之所以会发生这种情况,是因为useEffect是在第一次渲染之后执行的,因此,第一次用户为null时,一旦用户中有数据,就需要保护代码以进行渲染
return user ? <div className=“app”><NavBar user={user}/></div> : <div>loading</div>)
日志多次打印是因为严格的开发模式
答案 1 :(得分:0)
在您的第一个渲染中:您的用户是未定义的,这是正常的,因为未在使用状态中定义您的默认值,您可以通过此const [user, setUser] = useState({})
或此
import React, {useState, useEffect} from "react";
import NavBar from "./component/NavBar";
import Navigation from "./component/Navigation"
import Cookie from "js-cookie"
import axios from "axios"
import "./App.css";
function App() {
const [user, setUser] = useState()
const [logged, setLogged] = useState(false)
const cookie = Cookie.get("login")
useEffect(() => {
axios.post('/getdatafromcookie', cookie)
.then((res) => {
if(res.data.success === true){
setLogged(true)
setUser(res.data.user)
}
})
}, [])
console.log(user)
return (
<div className="App">
<header className="NavHeader">
{user ? <NavBar user={user} logged={logged} /> : "loading"}
</header>
{user ? <Navigation user={user} logged={logged}: "loading" />
</div>
);
}
export default App;
答案 2 :(得分:0)
问题是我不知道为什么以及何时尝试使用道具在其他组件中获取user.id时,我的tpyerror id未定义。
这样做的原因是,您尝试在加载用户之前获取用户的ID ,这意味着您正在执行null.id
之类的未定义操作(取决于在没有任何参数的情况下,useState
返回的内容可能是null)
在console.log
中获得多个Undefined的原因是:
第一次呈现App
组件时,useEffect
尚未完成对api的调用,因此user
仍为undefined
,第二次是因为您称为setLogged(true)
,因此用户仍然是undefined
,第3次和第4次...我不确定,但是您可能会以某种方式更改状态,从而导致重新渲染
解决此问题的适当等待时间是等待user
为defined
(即api调用完成)之后,您可以使用简单的if
语句来做到这一点,像
if (user.id) {
// return components when the user is logged in
} else {
// return components where the user is not logged in, usually a "loading" screen
}
现在您说user.id
返回type error
,但是我在您的代码中找不到任何user.id
,所以我以为您没有发布全部内容。