Question

所以我在Gatsby应用程序中使用React的上下文API（基本上是用React写的）来处理用户身份验证。我有两个使用该上下文的组件：dashboard和navBar。当我尝试登录和注销时，我的navBar会根据我的userContext的行为而有所不同，但是我的dashboard不会响应。它与结构有关吗，例如navBar是layout的直接“孩子”，而dashboard不是？毕竟我不认为这就是为什么我使用contextAPI然后仅仅通过一个正常的道具。

以下是代码：

//layout.js
import React, { useContext, useState, createContext } from "react"
import Navbar from "../components/navBar"
import {monitorAuth} from "../firebase/firebaseService"

export const UserStateContext = createContext(null)
export const SetUserContext = createContext()

const Layout = ({ children }) => {
  const [user, setUser] = useState()
  console.log(user)

  monitorAuth(setUser)// everytime a layout component renders, it will grab a user if it is logged inthen setUser, then I will use it in the context

  return (
    <>
      <UserStateContext.Provider value={user}>
        <SetUserContext.Provider value={setUser}>
          <div>
            <SEO />
            <Navbar />
            <main>{children}</main>
          </div>
        </SetUserContext.Provider >
      </UserStateContext.Provider>
    </>
  )
}


export default Layout

import React, { useState, useContext } from "react"
import AppBar from "@material-ui/core/AppBar"
import { signOut } from "../firebase/firebaseService"
import {UserStateContext} from "./layout"

export default function NavBar() {
  const user = useContext(UserStateContext)
  console.log(user) // when I log in/ log out, it will console.log the right user status, user/null

  const renderMenu = () => {
    return (
    <>
      {user? (
      <>
      <Button onClick={signOut}>Sign Out</Button>
      <Button>My profile</Button> 
      </>)
     :<Button>Sign In</Button> }
    </>
    )
  }

  return (
    <AppBar position="static" className={classes.root}>
        ...
        {renderMenu()}
        ...
  </AppBar>
  )
}

//dashboard.js
import React, { useContext } from 'react'
import Layout from '../components/layout'
import LoggedIn from '../components/dashboard/loggedIn'
import NotLoggedIn from '../components/dashboard/notLoggedIn'
import {UserStateContext} from "../components/layout"


const Dashboard = props => {
    console.log("within dashboard")
    const user = useContext(UserStateContext)
    console.log(user)

    const renderDashboard = () =>{
       return (
         <>
         {user? <LoggedIn /> : <NotLoggedIn />}
         </>
         
       )
    }

    return(
      <Layout>
        {renderDashboard()}
      </Layout>
    )
}

export default Dashboard

还有一个线索，我在所有三个组件中都用console.log user刷新页面时：

within dashboard
dashboard.js:17 null
layout.js:15 undefined
navBar.jsx:54 undefined
layout.js:15 [user...]
navBar.jsx:54 [user...]
layout.js:15 [user...]

这意味着，起初尚未设置user，因此所有三个组件都将user记录为undefined，但后来，layout 检测到{{1 }}，然后对其进行更新，因此user也知道，但navbar不知道。与dashboard有关吗？谢谢！

Answer 1

它不起作用的原因是因为您的<Dashboard>组件不是上下文提供程序的子级。如果您使用React devtools，您会看到组件树看起来像

<Dashboard>
  <Layout>
    <UserStateContext.Provider>
      <SetUserContext.Provider>
        ...
      </SetUserContext.Provider> 
    </UserStateContext.Provider> 
  </Layout>
</Dashboard>

当上下文值更改时，它将在其子树中寻找useContext的组件。但是，Dashboard不是孩子，而是父母！

如果要遵循这种模式，一个解决方案可能是创建Dashboard的父组件并将上下文放在那里。

为什么上下文值更新时我的上下文不更新？

1 个答案: