[英]In ReactJS, why child components re renders on dispatch in specific child component?
[英]React Component - Why can dispatch in AsyncApp Components
参考这个例子https://redux.js.org/advanced/example-reddit-api
import React, { Component } from 'react'
import PropTypes from 'prop-types'
import { connect } from 'react-redux'
import {
selectSubreddit,
fetchPostsIfNeeded,
invalidateSubreddit
} from '../actions'
import Picker from '../components/Picker'
import Posts from '../components/Posts'
class AsyncApp extends Component {
constructor(props) {
super(props)
this.handleChange = this.handleChange.bind(this)
this.handleRefreshClick = this.handleRefreshClick.bind(this)
}
componentDidMount() {
const { dispatch, selectedSubreddit } = this.props
dispatch(fetchPostsIfNeeded(selectedSubreddit))
}
componentDidUpdate(prevProps) {
if (this.props.selectedSubreddit !== prevProps.selectedSubreddit) {
const { dispatch, selectedSubreddit } = this.props
dispatch(fetchPostsIfNeeded(selectedSubreddit))
}
}
handleChange(nextSubreddit) {
this.props.dispatch(selectSubreddit(nextSubreddit))
this.props.dispatch(fetchPostsIfNeeded(nextSubreddit))
}
handleRefreshClick(e) {
e.preventDefault()
const { dispatch, selectedSubreddit } = this.props
dispatch(invalidateSubreddit(selectedSubreddit))
dispatch(fetchPostsIfNeeded(selectedSubreddit))
}
render() {
const { selectedSubreddit, posts, isFetching, lastUpdated } = this.props
return (
<div>
<Picker
value={selectedSubreddit}
onChange={this.handleChange}
options={['reactjs', 'frontend']}
/>
<p>
{lastUpdated && (
<span>
Last updated at {new Date(lastUpdated).toLocaleTimeString()}.{' '}
</span>
)}
{!isFetching && (
<button onClick={this.handleRefreshClick}>Refresh</button>
)}
</p>
{isFetching && posts.length === 0 && <h2>Loading...</h2>}
{!isFetching && posts.length === 0 && <h2>Empty.</h2>}
{posts.length > 0 && (
<div style={{ opacity: isFetching ? 0.5 : 1 }}>
<Posts posts={posts} />
</div>
)}
</div>
)
}
}
AsyncApp.propTypes = {
selectedSubreddit: PropTypes.string.isRequired,
posts: PropTypes.array.isRequired,
isFetching: PropTypes.bool.isRequired,
lastUpdated: PropTypes.number,
dispatch: PropTypes.func.isRequired
}
function mapStateToProps(state) {
const { selectedSubreddit, postsBySubreddit } = state
const { isFetching, lastUpdated, items: posts } = postsBySubreddit[
selectedSubreddit
] || {
isFetching: true,
items: []
}
return {
selectedSubreddit,
posts,
isFetching,
lastUpdated
}
}
导出默认连接(mapStateToProps)(AsyncApp)
function 可以使用 this.props.dispatch(fetchPostsIfNeeded(nextSubreddit)) 触发“fetchPostsIfNeeded”等动作。 但是,它假设与 mapDispatchToProps 有关。 所以我可以知道为什么程序运行成功且没有错误的场景
欢迎来到 SO。
实际上, connect()
已经为您的组件提供了调度。( https://react-redux.js.org/api/connect#example-usage )
你可以将mapDispatchToProps
作为一个中间件来创建带有调度的方法。
假设我们有一家带有 state 柜台的商店。
{
counter: 0
}
在mapDispatchToProps
中,我们可以在这个组件中使用创建方法:
{
increment: ()=>{dispatch({ type: 'EDIT', payload: 1 })},
decrement: ()=>{dispatch({ type: 'EDIT', payload: -1 })}
}
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