如何解决反应：setState不会导致重新渲染吗？

我是React，JS，JSX的新手。

setNewWeather似乎没有正确更新天气状态，因为它是由初始值定义的，但是随后变为undefined。

因为它更新了，应该引起重新渲染；我看过很多关于此的文章，但他们建议喜欢，等待异步数据操作，但是据我了解，使用'.then'方法具有内在的功能吗？还是涉及setNewWeather语法的另一个问题，例如它需要在内部使用一个函数而不只是一个字符串来更新状态？

我的代码：

import React,{ useState,useEffect } from 'react'
import axios from 'axios'

const Header = ({ text }) => <h1>{text}</h1>
const Header3 = ({ text }) => <h3>{text}</h3>
const Image = ({ source,alttext }) => <img src={source} alt={alttext} />
const Button = ({ onClick,text }) => (<button onClick={onClick}>{text}</button>)
const ListItem = ({ item }) => <li>{item}</li>
const List = ({ title,stuff }) => {
  return(
    <>
    < Header3 text={title} />
    <ul>
      {stuff.map((item,index) => < ListItem key={index} item={item} />)}
    </ul>
    </>)}
const Search = ({ text,value,onChange }) => {
  return (
    <>
    {text}
    <input value={value} onChange={onChange} />
    </>)}

const CountryMany = ({ country,handleClick }) => {
  return (
    <>
    <li>{country.name}</li>
    < Button onClick={handleClick(country.name)} text='Show' />
    </>)}

const CountryFound = ({ country,api_key,handleWeather,newWeather }) => {
  const countryFound = country[0]
  const params = {
    access_key: api_key,query: countryFound.capital
  }
  useEffect(() => {
    axios.get('http://api.weatherstack.com/current',{params})
         .then(response => {
          console.log('RESPONSE',response.data)
          handleWeather({ is: 'weather',data: response.data })
          console.log(newWeather)
          })},[params,newWeather,handleWeather])
  console.log('yo')
  console.log(newWeather)

  const languages = countryFound.languages.map(lang => lang.name)
  return (
    <>
    < Header text={countryFound.name} />
    <p>Capital: {countryFound.capital}</p>
    <p>Population: {countryFound.population}</p>
    < List title='Languages' stuff={languages} />
    < Header3 text='Flag' />
    < Image source={countryFound.flag} alttext='flag' />
    < Header3 text='Weather' />
    <ul>
      <li>Temperature: {newWeather}</li>
      <li> Image source= alttext=weather </li>
    </ul></>)}

const Countries = (props) => {
  console.log('COUNTRIES PROPS',props)
  console.log('WEATHER',props.newWeather)
  const countries = props.countries
  const foundCountries = countries.filter(country =>
    country.name.toLowerCase().includes(props.newSearch.toLowerCase()))
  if (foundCountries.length > 10 ) {
    return (<p>Too Many Matches,Keep Typing!</p>)}
  if (foundCountries.length > 1) {
    return (
        <ul>
        {foundCountries.map(country =>
        < CountryMany key={country.population} country={country} handleClick={props.handleClick} />)}
        </ul>)}
  if (foundCountries.length === 1) {
    return (
        <>
          <CountryFound api_key={props.a_k1} country={foundCountries}
            handleWeather={props.handleWeather} weather={props.newWeather} />
        </>)}
  return (<></>)}

const App = () => {
  const api_key = process.env.REACT_APP_API_KEY
  const [ countries,setCountries ] = useState([])
  const [ newSearch,setNewSearch ] = useState('')
  const [ newWeather,setWeather ] = useState({ is: 'no ewather' })
  const handleWeather = ( is,data ) => () => {
    setWeather( is,data )
    console.log('HEY HANDLEWEATHER',newWeather)}
  
  useEffect(() => {
    axios
      .get('https://restcountries.eu/rest/v2/all')
      .then(response => {
        setCountries(response.data)
      })},[])
  
  const handleClick = (value) => () => {
          setNewSearch(value)}
  const handleSearch = (event) => {
          setNewSearch(event.target.value)}
  
  return (
    <div>
      < Search text='Find A Country: ' value={newSearch} onChange={handleSearch}/>
      < Countries countries={countries} 
                  a_k1={api_key} 
                  handleWeather={handleWeather}
                  handleClick={handleClick} 
                  newSearch={newSearch}
                  newWeather={newWeather}
                   />
    </div>)}

export default App

/*
const Weather = ({ weather }) => {
    return (
    <>
    < Header3 text='Weather' />
    <ul>
      <li>Temperature: weather.temperature</li>
      <li> Image source= alttext=weather </li>
    </ul>
    </>)}
    */

谢谢！

编辑：状态正在更新，但只能通过形成无限循环来实现：

import React,handleClick }) => {
  return (
    <>
    <li>{country.name}</li>
    < Button onClick={handleClick(country.name)} text='Show' />
    </>)}

const CountryFound = ({ countryFound,newWeather }) => {
  const params = { access_key: api_key,query: countryFound.capital }
  useEffect(() => {
    axios.get('http://api.weatherstack.com/current',response.data)
          handleWeather(response.data)
          })})
  
  
  const languages = countryFound.languages.map(lang => lang.name)
  if (newWeather.length >  0 ){
    return (
      <>
      < Header text={countryFound.name} />
      <p>Capital: {countryFound.capital}</p>
      <p>Population: {countryFound.population}</p>
      < List title='Languages' stuff={languages} />
      < Header3 text='Flag' />
      < Image source={countryFound.flag} alttext='flag' />
      < Header3 text='Weather' />
      <ul>
      <li>Temperature/rendering {newWeather}</li>
      <li> Image source= alttext=weather </li>
      </ul></>)}
  return (
    <></>
  )}
  

const Countries = (props) => {
  console.log('COUNTRIES PROPS',props.newWeather)
  const foundCountries = props.countries.filter(country =>
    country.name.toLowerCase().includes(props.newSearch.toLowerCase()))
  if (foundCountries.length > 10 ) {
    return (<p>Too Many Matches,Keep Typing!</p>)}
  if (foundCountries.length > 1) {
    return (
        <ul>
        {foundCountries.map(country =>
        < CountryMany key={country.population} country={country} handleClick={props.handleClick} />)}
        </ul>)}
  if (foundCountries.length === 1) {
    return (
        <>
          <CountryFound api_key={props.a_k1} countryFound={foundCountries[0]}
            handleWeather={props.handleWeather} newWeather={props.newWeather} />
        </>)}
  return (<></>)}

const App = () => {
  const api_key = process.env.REACT_APP_API_KEY
  const [ countries,setNewSearch ] = useState('af')
  const [ newWeather,setWeather ] = useState([])
  const handleClick = (value) => () => {
        setNewSearch(value)}
  const handleSearch = (event) => {
        setNewSearch(event.target.value)}

  useEffect(() => {
    axios
      .get('https://restcountries.eu/rest/v2/all')
      .then(response => {
        setCountries(response.data)
      })},[])
  return (
    <div>
      < Search text='Find A Country: ' value={newSearch} onChange={handleSearch}/>
      < Countries countries={countries} 
                  a_k1={api_key} 
                  handleWeather={setWeather}
                  handleClick={handleClick} 
                  newSearch={newSearch}
                  newWeather={newWeather}
                   />
    </div>)}

export default App

最终编辑：已解决！

以下标记的解决方案解决了初始问题，但产生了无限循环。我已经整顿了整件事，尽管我还不太了解它是如何改变的。

import React,index) => < ListItem key={index} item={item} />)}
    </ul>
    </>)}

const Search = ({ text,newWeather }) => {
  useEffect(() => {
    axios.get(`https://api.weatherbit.io/v2.0/current?city=${countryFound.capital}&key=${api_key}`)
          .then(response => {
          handleWeather(response.data.data[0])
          })})
  const languages = countryFound.languages.map(lang => lang.name)
  if (newWeather > '' ) {
    const capital = countryFound.capital
    const weatherTitle = `Weather in: ${capital}`
    const weatherImage = `https://www.weatherbit.io/static/img/icons/${newWeather.weather.icon}.png`
    return (
      <>
      < Header text={countryFound.name} />
      <p>Capital: {capital}</p>
      <p>Population: {countryFound.population}</p>
      < List title='Languages' stuff={languages} />
      < Header3 text='Flag' />
      < Image source={countryFound.flag} alttext='flag' />
      < Header3 text={weatherTitle} />
      < Image source={weatherImage} alttext='weather' />
      <ul>
      <li>Temperature: {newWeather.temp} degrees Celsius</li>
      <li>Wind: {newWeather.wind_spd} mph towards {newWeather.wind_cdir}</li>
      </ul></>)}
  return (<><p>Loading...</p></>)}
  
const Countries = (props) => {
  const foundCountries = props.countries.filter(country =>
    country.name.toLowerCase().includes(props.newSearch.toLowerCase()))
  if (foundCountries.length > 10 ) {
    return (<p>Too Many Matches,Keep Typing!</p>)}
  
  if (foundCountries.length > 1) {
    return (
        <ul>
        {foundCountries.map(country =>
        < CountryMany key={country.population} 
                      country={country} 
                      handleClick={props.handleClick} />)}
        </ul>)}
  
  if (foundCountries.length === 1) {
    return (<>
          <CountryFound api_key={props.a_k1} countryFound={foundCountries[0]}
            handleWeather={props.handleWeather} newWeather={props.newWeather} />
            </>)}
  return (<></>)}

const App = () => {
  const api_key = process.env.REACT_APP_API_KEY
  const [ countries,setWeather ] = useState('')
  const handleClick = (value) => () => {
        setNewSearch(value)}
  const handleSearch = (event) => {
        setNewSearch(event.target.value)}

  useEffect(() => {
    axios
      .get('https://restcountries.eu/rest/v2/all')
      .then(response => {
        setCountries(response.data)
      })},[])

  return (
    <div>
      < Search text='Find A Country: ' value={newSearch} onChange={handleSearch}/>
      < Countries countries={countries} 
                  a_k1={api_key} 
                  handleWeather={setWeather}
                  handleClick={handleClick} 
                  newSearch={newSearch}
                  newWeather={newWeather}
                   />
    </div>)}

export default App

解决方法

问题

handleWeather定义为带有两个参数

const handleWeather = ( is,data ) => () => {
  setWeather( is,data )
  console.log('HEY HANDLEWEATHER',newWeather)
}

但是当您调用它时，您只能传递一个参数

handleWeather({ is: 'weather',data: response.data })

此外，反应状态更新是异步的，并且在渲染周期之间是批量处理的，因此尝试在入队后立即控制台日志状态只会记录当前状态。

解决方案

您应该选择接受两个参数并创建您想要的状态对象，或者将要存储的已创建对象始终传递给它。以下将使用后者。

const handleWeather = (newWeather) => () => setWeather(newWeather);

注意：目前，handleWeather只是代理newWeather对象，因此较小的优化可能不是代理，因为函数签名匹配，即const handleWeather = setWeather，或者直接传递setWeather作为回调。

<Countries
  countries={countries} 
  a_k1={api_key} 
  handleWeather={setWeather} // <-- directly pass state update function
  handleClick={handleClick} 
  newSearch={newSearch}
  newWeather={newWeather}
/>

使用效果来记录更新的newWeather，并使用newWeather作为依赖项。

useEffect(() => {
  console.log('HEY HANDLEWEATHER',newWeather)
},[newWeather]);

反应：setState不会导致重新渲染吗？

如何解决反应：setState不会导致重新渲染吗？

解决方法

问题

解决方案

相关推荐