我有一个简单的应用程序,它可以获取一些天气JSON并显示它。用户可以输入一个位置,也可以点击“获取幸运”按钮,该按钮可以获取随机城市。初始状态在App.js中设置
this.state = {
error: '',
status: '',
queryString: 'london,gb',
queryID: '',
queryType: 'q',
cityData: cityData,
weatherData: {},
isLoaded: false
}
接下来,我有我的主App类,然后我有一个名为的子组件包含表单gubbins。我在app render中调用它如下:
<SearchForm
queryString={this.state.queryString}
handleChange={this.handleChange}
setQueryType={this.setQueryType}
setQueryID={this.setQueryID}
getWeatherData={this.getWeatherData}
/>
我在那里使用回调函数来设置查询类型(位置或ID)。 App.js中一个回调函数的示例是:
setQueryType = (queryType) => {
this.setState({
queryType: queryType
})
}
这是以JS形式调用的:
props.setQueryType(e.target.attributes.query.value)
现在,问题的症结在于:州第一次没有更新,但第二次点击是否有效?实际上,在第二次单击之前,不会设置其他变量,如fetch中设置的queryString。
App.js
import React, { Component } from 'react';
import './css/App.css';
import WeatherCard from './components/WeatherCard'
import Header from './components/Header'
import SearchForm from './components/SearchForm'
import cityData from './json/city.list'
const config = {
API: 'https://api.openweathermap.org/data/2.5/forecast',
API_KEY: process.env.REACT_APP_OPEN_WEATHER_MAP_API_KEY
}
class App extends Component {
constructor() {
super()
this.state = {
error: '',
status: '',
queryString: 'london,gb',
queryID: '',
queryType: 'q',
cityData: cityData,
weatherData: {},
isLoaded: false
}
this.getWeatherData()
}
getWeatherData = (searchValue="london,gb") => {
let URL
URL = config.API + '?' + this.state.queryType + '='
URL += this.state.queryType === 'q' ? searchValue : this.state.queryID
URL += '&units=metric&APPID=' + config.API_KEY
console.log(URL)
fetch(URL)
.then( result => result.json() )
.then (
(result) => {
if ( result.cod === '200') {
this.setState({
status: result.cod,
weatherData: result,
queryString: result.city.name,
isLoaded: true
})
} else {
this.setState({
status: result.cod,
error: result.message,
isLoaded: false
})
}
},
(error) => {
this.setState({
isLoaded: false,
error: error
})
}
)
console.log(this.state.queryString)
}
handleChange = (event) => {
const { name, value } = event.target
this.setState({
[name]: value
})
}
getWeatherCards = () => {
let cards = []
for (let i = 0; i < this.state.weatherData.cnt; i++) {
cards.push(
<WeatherCard
key={i}
weatherList={this.state.weatherData.list[i]}
/>
)
}
return cards
}
setQueryType = (queryType) => {
this.setState({
queryType: queryType
})
}
setQueryID = () => {
let randomID = Math.floor(Math.random() * this.state.cityData.length)
let randomCityID = this.state.cityData[randomID].id
this.setState({
queryID: randomCityID
})
}
getlocationForm = () => {
return(
<SearchForm
queryString={this.state.queryString}
handleChange={this.handleChange}
setQueryType={this.setQueryType}
setQueryID={this.setQueryID}
getWeatherData={this.getWeatherData}
/>
)
}
render = () => {
if (this.state.status !== '200') {
return (
<div className='App'>
<Header
status={this.state.status}
error={this.state.error}
/>
{this.getlocationForm()}
</div>
)
} else {
return (
<div className='App'>
{
this.state.isLoaded && (
<Header
cityName={this.state.weatherData.city.name}
countryName={this.state.weatherData.city.country}
status={this.state.status}
error={this.state.error}
/>
)
}
{this.getlocationForm()}
{
this.state.isLoaded && (
<div className='weather-cards'>
{this.getWeatherCards()}
</div>
)
}
</div>
)
}
}
}
export default App;
SearchForm.js
import React from 'react'
const SearchForm = (props) => {
let handleChange = function(e) {
props.handleChange(e)
}
let handleClick = function(e) {
e.preventDefault()
props.setQueryType(e.target.attributes.query.value)
if (e.target.attributes.query.value === 'id') {
props.setQueryID()
}
props.getWeatherData()
}
return (
<div>
<form className="search-form">
<input
type="text"
id="query"
name="query"
placeholder="Enter a location..."
onChange={handleChange}
/>
<button
type="submit"
query="q"
onClick={handleClick}
>
Submit
</button>
<button
type="submit"
query="id"
onClick={handleClick}
>
I'm feeling lucky...
</button>
</form>
</div>
)
}
export default SearchForm
我认为问题来自这样一个事实:当你调用getWeatherData
时,你不知道setState
是否会结束,因为它是一个异步方法。 (正如你在documentation中看到的那样)
因此,最好的方法是确保在调用方法之前完成setState
而不确定组件的状态,将使用setState的callBack参数来确保它在setState
方法完成后运行。
在你的App.js
构造函数中添加this.setQueryType = this.setQueryType.bind(this)
该行将this
的上下文绑定到当前组件,因此从子进程调用时,将更新父状态。
尝试将this.getWeatherData()放入componentDidMount并从构造函数中删除它
componentDidMount() {
this.getWeatherData()
}