我正在学习 helinski fsopen20 的反应。其中一个练习需要单击一个按钮并显示该按钮绑定区域的天气。
该按钮有一个 onClick 事件，该事件将区域索引作为参数来确定选择哪个区域（显然）。
<button onClick={() => onClickShow(i)}>{showBox.includes(i) ? myfunction(i): 'show'}</button>
OnClick 函数然后呈现所述区域的详细信息。需要获取的数据是在这个函数内部完成的
const myfunction = useCallback((i)=>{ // the 'i' is passed
axios.get('http://api.weatherstack.com/current'
+ `?access_key=${process.env.REACT_APP_API_KEY}`
+`&query=${searchResult[i].name}`)
.then(response=>{
setWeather(response.data)
})
console.log(weather); //this re-renders to infinity
return[
<h2 key='name'>{searchResult[i].name}</h2>,
<h2 key='sth'>Capital weather: {weather}</h2> // I will beautify this function later
]
},[searchResult, weather])
useEffect(()=>{
},[myfunction])
我能够实现我想要的，但它需要大量的重新渲染。
最初使用 axios get() 没有 useEffect 或 useCallback 导致无限重新渲染但令我惊讶的是，
我试过 useEffect 和 useCallBack() 但没有什么能阻止重新渲染。
在旁注中，我在我的 App 组件中使用了不同的 useEffect ，它渲染一次就好了。
如何正确使用 useEffect 和 onClick 等事件处理函数？
下面是完整的代码：
import React,{useState, useEffect, useCallback} from 'react'
import axios from 'axios'
const Helper=({searchResult})=>{
const [showBox, setShowBox] = useState([])
const [weather, setWeather] = useState([])
const onClickShow = (index) => setShowBox(showBox.concat(index))
const myfunction = useCallback((i)=>{
axios.get('http://api.weatherstack.com/current'
+ `?access_key=${process.env.REACT_APP_API_KEY}`
+`&query=${searchResult[i].name}`)
.then(response=>{
setWeather(response.data)
})
console.log(weather); /////// INFINTE RE-RENDER
return[
<h2 key='name'>{searchResult[i].name}</h2>,
<p key='capital'>{searchResult[i].capital}</p>,
<p key='popn'>{searchResult[i].population}</p>,
<h3 key='langs'>Languages</h3>,
<ul key='lang'>{searchResult[i].languages.map(lang => <li key={lang.iso639_1}>{lang.name}</li>)}</ul>,
<img key='img' src={searchResult[i].flag} alt="flag" width="100" height="100" object-fit="fill"/>
/* searchResult.map(result=><h2 key={result.population}>{result.name}<br/></h2>),
// searchResult.map(result=><p key={result.population}> {result.capital} <br/> {result.population}</p>),
// <h3 key="id">Languages</h3>,
// searchResult.map(result=> <ul key={result.population}>{result.languages.map(lang => <li key={lang.iso639_1}>{lang.name}</li>)}</ul>),
// searchResult.map(result=><img src={result.flag} alt="flag" width="100" height="100" object-fit="fill" key={result.population}/>)
*/
]
},[searchResult, weather])
useEffect(()=>{
},[myfunction])
if(searchResult.length === 1){
return(
<div>
{myfunction(0)}
</div>
)
}
else{
return(
<>
{
searchResult.length <= 10 ?
searchResult.map((result,i) => <h3 key={result.name}> {result.name}
<button onClick={() => onClickShow(i)}>{showBox.includes(i) ? myfunction(i): 'show'}</button></h3>)
: searchResult
}
</>
)
}
}
const App =()=>{
/// store all countries fetched
const [countries, setCountries] = useState([])
// store each searched country
const [searchName, setSearchName] = useState([])
//store the result country
const [searchResult, setSearchResult] = useState([])
useEffect(()=>{
axios.get('https://restcountries.eu/rest/v2/all')
.then(response=>{
setCountries(response.data)
})
}, [])
const handleSearch = (event) =>{
setSearchName(event.target.value)
if (searchName.length !== 0){
var found = searchName ? countries.filter(country => country.name.toUpperCase().includes(searchName.toUpperCase())) : countries
if(found.length > 10){
setSearchResult("Too many matches, specify another filter")
}
else if(found.length === 1){
setSearchResult(found)
}
else if(found.length === 0){
setSearchResult(found)
}
else{
setSearchResult(found)
}
}
}
return(
<>
<h1>find countries <input value={searchName} onChange={handleSearch} /></h1>
<Helper searchResult={searchResult} />
</>
)
}
export default App;