React Native setState(..):无法在现有状态转换期间进行更新

Question

我目前正在开发一款React Native应用程序，该应用程序的屏幕上有一个自定义的滑动器组件，允许用户在一组照片中滑动。最初，我做了一个API调用，加载10张照片，当当前照片索引接近他们存储的数组的末尾时，用户可以滑动加载另外10张照片

由于我正在进行分页，我想跟踪用户在哪个页面上。例如，如果索引在0-9之间，则用户在第一页上，第二页为10-19，等等。

我已经能够成功地跟踪用户所在的页面，但在状态内更新时会生成一个警告，这让我觉得有更好的方法来处理这个问题。

Warning: setState(...): Cannot update during an existing state transition
(such as within `render` or another component's constructor). Render
methods should be a pure function of props and state; constructor side
effects are an anti-pattern, but can be moved to `componentWillMount`.

这是我的屏幕实现：

'use strict'
import React, { Component } from 'react'
import { Text, View, Image, Dimensions, Platform } from 'react-native'
import { StackNavigator } from 'react-navigation'
import Swiper from 'react-native-swiper'
import styles from './styles/ImageScreenStyle'
const { width, height } = Dimensions.get('window')
class ImageScreen extends Component {
constructor(props) {
super(props)
this.state = {
page: this.props.navigation.state.params.page,
key: this.props.navigation.state.params.key,
items: this.props.navigation.state.params.array,
}
this._fetchNextPage = this._fetchNextPage.bind(this)
this._renderNewItems = this._renderNewItems.bind(this)
this._renderNewPage = this._renderNewPage.bind(this)
}
// Update the parent state to push in new items
_renderNewItems(index, items) {
let oldItems = this.state.items
let newItems = oldItems.concat(items)
this.setState({ items: newItems, key: index })
}
// This generates a warning but still works?
_renderNewPage(page) {
let newPage = this.state.page
newPage.current = page
this.setState({ page: newPage })
}
render() {
return (
<Swiper
showsButtons
loop = { false }
index = { this.state.key }
renderPagination = { this._renderPagination }
renderNewItems = { this._renderNewItems }
renderNewPage = { this._renderNewPage }
fetchNextPage = { this._fetchNextPage }
page = { this.state.page }>
{ this.state.items.map((item, key) => {
return (
<View key = { key } style = { styles.slide }>
<Image
style = {{ width, height }}
resizeMode = 'contain'
source = {{ uri: item.photo.images[1].url }}
/>
</View>
)
})}
</Swiper>
)
}
_renderPagination(index, total, context) {
const photoPage = Math.floor(index / 10) + 1
const currentPage = this.page.current
// Update the current page user is on
if (photoPage !== currentPage) {
return this.renderNewPage(photoPage)
}
// Add more photos when index is greater or equal than second last item
if (index >= (total - 3)) {
this.fetchNextPage().then((data) => {
// Here is where we will update the state
const photos = data.photos
let items = Array.apply(null, Array(photos.length)).map((v, i) => {
return { id: i, photo: photos[i] }
})
// Pass in the index because we want to retain our location
return this.renderNewItems(index, items)
})
}
}
_fetchNextPage() {
return new Promise((resolve, reject) => {
const currentPage = this.state.page.current
const nextPage = currentPage + 1
const totalPages = this.state.page.total
if (nextPage < totalPages) {
const PAGE_URL = '&page=' + nextPage
fetch(COLLECTION_URL + PAGE_URL + CONSUMER_KEY)
.then((response) => {
return response.json()
})
.then((data) => {
return resolve(data)
})
.catch((error) => {
return reject(error)
})
}
})
}
}
export default ImageScreen

分页是在一个函数中处理的，我使用_renderNewItems和_renderNewPage方法来处理新照片和页面索引的状态。

更新

我已经修改了代码以反映所提供的答案，但没有任何运气得到要抑制的警告。我认为绑定和更改为componentWillMount()方法会有所帮助。以下是我目前的立场：

class ImageScreen extends Component {
constructor(props) {
super(props)
this.state = {
page: '',
key: '',
items: []
}
this._fetchNextPage = this._fetchNextPage.bind(this)
this._renderNewItems = this._renderNewItems.bind(this)
this._renderNewPage = this._renderNewPage.bind(this)
}
componentWillMount() {
this.setState({
page: this.props.navigation.state.params.page,
key: this.props.navigation.state.params.key,
items: this.props.navigation.state.params.array
})
}
render() {
return (
<Swiper
showsButtons
loop = { false }
index = { this.state.key }
renderPagination = { this._renderPagination.bind(this) }
renderNewItems = { this._renderNewItems.bind(this) }
renderNewPage = { this._renderNewPage.bind(this) }
fetchNextPage = { this._fetchNextPage.bind(this) }>
{ this.state.items.map((item, key) => {
return (
<View key = { key } style = { styles.slide }>
<Image
style = {{ width, height }}
resizeMode = 'contain'
source = {{ uri: item.photo.images[1].url }}
/>
</View>
)
})}
</Swiper>
)
}
_renderPagination(index, total, context) {
const photoPage = Math.floor(index / 10) + 1
const statePage = this.state.page.current
if (photoPage !== statePage) {
return this._renderNewPage(photoPage)
}

if (index >= (total - 3)) {
this._fetchNextPage().then((data) => {
const photos = data.photos
let items = Array.apply(null, Array(photos.length)).map((v, i) => {
return { id: i, photo: photos[i] }
})
return this._renderNewItems(index, items)
})
}
}
_renderNewItems(index, items) {
let oldItems = this.state.items
let newItems = oldItems.concat(items)
this.setState({ items: newItems, key: index })
}
// TO-DO: Fix the warning this generates
_renderNewPage(page) {
let newPage = this.state.page
newPage.current = page
this.setState({ page: newPage })
}
_fetchNextPage() {
return new Promise((resolve, reject) => {
const currentPage = this.state.page.current
const nextPage = currentPage + 1
const totalPages = this.state.page.total
if (nextPage < totalPages) {
const PAGE_URL = '&page=' + nextPage
fetch(COLLECTION_URL + PAGE_URL + CONSUMER_KEY)
.then((response) => {
return response.json()
})
.then((data) => {
return resolve(data)
})
.catch((error) => {
return reject(error)
})
}
})
}
}
export default ImageScreen

更新2

修复了问题。正如Felix在评论中指出的那样，renderPagination方法经常被重新渲染，所以我使用Swiper的onMomentumScrollEnd道具(来自react native swipper)来更新页面信息。对于任何可能需要它的人，这里是我的代码：

class ImageScreen extends Component {
constructor(props) {
super(props)
this.state = {
page: '',
key: '',
items: []
}
}
componentWillMount() {
this.setState({
page: this.props.navigation.state.params.page,
key: this.props.navigation.state.params.key,
items: this.props.navigation.state.params.array
})
}
render() {
return (
<Swiper
showsButtons
loop = { false }
index = { this.state.key }
onMomentumScrollEnd = { this._onMomentumScrollEnd.bind(this) }
renderPagination = { this._renderPagination.bind(this) }
renderNewItems = { this._renderNewItems.bind(this) }
fetchNextPage = { this._fetchNextPage.bind(this) }>
{ this.state.items.map((item, key) => {
return (
<View key = { key } style = { styles.slide }>
<Image
style = {{ width, height }}
resizeMode = 'contain'
source = {{ uri: item.photo.images[1].url }}
/>
</View>
)
})}
</Swiper>
)
}
_renderNewItems(index, items) {
let oldItems = this.state.items
let newItems = oldItems.concat(items)
this.setState({ items: newItems, key: index })
}
_renderPagination(index, total, context) {
if (index >= (total - 3)) {
this._fetchNextPage().then((data) => {
const photos = data.photos
let items = Array.apply(null, Array(photos.length)).map((v, i) => {
return { id: i, photo: photos[i] }
})
return this._renderNewItems(index, items)
})
}
}
_fetchNextPage() {
return new Promise((resolve, reject) => {
const currentPage = this.state.page.current
const nextPage = currentPage + 1
const totalPages = this.state.page.total
if (nextPage < totalPages) {
const PAGE_URL = '&page=' + nextPage
fetch(COLLECTION_URL + PAGE_URL + CONSUMER_KEY)
.then((response) => {
return response.json()
})
.then((data) => {
return resolve(data)
})
.catch((error) => {
return reject(error)
})
}
})
}
_onMomentumScrollEnd(e, state, context) {
const photoPage = Math.floor(state.index / 10) + 1
const statePage = this.state.page.current
console.log('Current page: ' + photoPage)
console.log('State page: ' + statePage)

if (photoPage !== statePage) {
this._renderNewPage(photoPage)
}
}
_renderNewPage(page) {
let newPage = this.state.page
newPage.current = page
this.setState({ page: newPage })
}
}
export default ImageScreen

Answer 1

使用应更新

shouldComponentUpdate();

如果以上不起作用，那么你也可以试试这个。

this.forceUpdate();

Answer 2

不确定，但我认为问题出在这一行：

renderPagination = { this._renderPagination }

您忘记了bind这个事件，而这正在创建loop，因为您在其中使用this.setState。试试这个：

renderPagination = { this._renderPagination.bind(this) }

原因：每当您再次使用this.setState、React、render和整个component时，如果您当时没有bind任何方法，它将在每个rendering期间被调用，除非您在该函数中没有使用setState，否则它不会产生任何问题，但如果您在其中使用setState，它将创建loop，它将再次调用rendersetState。。。。。。。