TypeError: Cannot read property 'name"' of undefined in react when passing object in useState

Question

我的问题是路由获取 json 格式的响应。当安慰它时它也给出数据但是当我传入 setProfileData(data) 然后更新状态给出未定义的。

但是当我给出类似 setProfileData(data.user.name) 时，它会给出特定值。

这是我的服务器路由

router.get('/user/:id',async(req,res)=>{
  try {
    const user = await User.findOne({_id:req.params.id}).select('-password')
    const post = await Post.find({postedBy:req.params.id}).populate('postedBy', '_id name')
    
    return res.json({user,post})
        
    } catch (error) {
        return res.json(error)
    }
})

这是我的组件用户配置文件

import React,{useContext,useEffect,useState} from 'react';
import {useHistory,useParams} from 'react-router-dom'
import {UserContext} from '../../App'

const UserProfile = ()=>{
    const [newProfile,setProfileData] = useState(null)
    const {state,dispatch} = useContext(UserContext)
    
    const {userId} = useParams()
    console.log(userId)
    useEffect(()=>{
        fetch(`/user/${userId}`,{
            headers:{
                'Authorization': 'Bearer '+localStorage.getItem('jwt')
            }
        }).then((res)=>{
            return res.json()
        }).then((data)=>{
            console.log(data)
           setProfileData(data)
            
        })
    },[])
    return (
        <div style={{width:'555px',margin:"0px auto"}}>
            <div style={{display:"flex",justifyContent:"space-around",margin:'18px 0px',borderBottom:"1px solid grey"}}>
                <div><img style={{width:"160px",height:"160px",borderRadius:"80px"}}
                src="https://images.unsplash.com/photo-1550927407-50e2bd128b81?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=500&q=60" alt="Profile Pic"/>
                </div>
                <div>
    <h4>{newProfile.user.name}</h4>
                 <div style={{display:"flex",justifyContent:"space-around",width:"108%"}}>
                     <h5>40 Posts</h5>
                     <h5>40 Followers</h5>
                     <h5>40 Followings</h5>
                 </div>
                 </div>
            </div>
            <div className="gallery">
                 {
                    // userProfile.map((item)=>{
                    //     return (
                    //         <img key={item._id} className="item" src={item.file} alt={item.title}/>
                    //     )
                    // })
                }
                
           
               
             
            </div>
        </div>
    );
}

export default UserProfile;

{newProfile.user.name} 给出类型未定义

Answer 1

当组件开始工作时，

newProfile 为空。在 render 方法中访问它之前必须检查：

  {newProfile != null ?
                        <div>
                            <h4>{newProfile.user.name}</h4>
                            <div style={{ display: "flex", justifyContent: "space-around", width: "108%" }}>
                                <h5>40 Posts</h5>
                                <h5>40 Followers</h5>
                                <h5>40 Followings</h5>
                            </div>
                        </div>
                        : 'loading'}

或者使用 useState 钩子中的默认值

完整版：

import React, { useContext, useEffect, useState } from 'react';
import { useHistory, useParams } from 'react-router-dom'
import { UserContext } from '../../App'
import { Divider } from 'material-ui';

const UserProfile = () => {
    const [newProfile, setProfileData] = useState(null)
    const { state, dispatch } = useContext(UserContext)

    const { userId } = useParams()
    console.log(userId)
    useEffect(() => {
        fetch(`/user/${userId}`, {
            headers: {
                'Authorization': 'Bearer ' + localStorage.getItem('jwt')
            }
        }).then((res) => {
            return res.json()
        }).then((data) => {
            console.log(data)
            setProfileData(data)

        })
    }, [])
    return (
        <div style={{ width: '555px', margin: "0px auto" }}>
            <div style={{ display: "flex", justifyContent: "space-around", margin: '18px 0px', borderBottom: "1px solid grey" }}>
                <div><img style={{ width: "160px", height: "160px", borderRadius: "80px" }}
                    src="https://images.unsplash.com/photo-1550927407-50e2bd128b81?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=500&q=60" alt="Profile Pic" />
                </div>
                <div>
                    {newProfile != null ?
                        <div>
                            <h4>{newProfile.user.name}</h4>
                            <div style={{ display: "flex", justifyContent: "space-around", width: "108%" }}>
                                <h5>40 Posts</h5>
                                <h5>40 Followers</h5>
                                <h5>40 Followings</h5>
                            </div>
                        </div>
                        : 'loading'}

                </div>
            </div>
            <div className="gallery">
            </div>
        </div>
    );
}

export default UserProfile;

TypeError: Cannot read property 'name"' of undefined in react when passing object in useState

TypeError: Cannot read property 'name"' of undefined in react when passing object in useState

javascript

mongodb

node.js

reactjs

use-state