Reactjs 如何避免每次选择/取消选择行时重新渲染本机平面列表
看到或看到 我尝试在react原生FlatList的基础上构建一个简单的可选列表。功能很简单:扁平列表中的每一行都是可选择的。如果尚未选择某一行,单击该行将选中该行;如果已选择该行,单击该行将取消选择该行 我面临的问题是,每次单击一行时,所有行都会重新渲染,这可以从日志中看出(例如“渲染项id=cameron”)。nguyen@example.com,selected=false”)。我希望避免对未更改的行进行重新渲染,因为重新渲染可能会很昂贵(在我希望加载非常大的图像或列表非常长的情况下),但我不知道如何进行。我已经尝试了Reactjs 如何避免每次选择/取消选择行时重新渲染本机平面列表,reactjs,react-native,react-hooks,react-native-flatlist,Reactjs,React Native,React Hooks,React Native Flatlist,看到或看到 我尝试在react原生FlatList的基础上构建一个简单的可选列表。功能很简单:扁平列表中的每一行都是可选择的。如果尚未选择某一行,单击该行将选中该行;如果已选择该行,单击该行将取消选择该行 我面临的问题是,每次单击一行时,所有行都会重新渲染,这可以从日志中看出(例如“渲染项id=cameron”)。nguyen@example.com,selected=false”)。我希望避免对未更改的行进行重新渲染,因为重新渲染可能会很昂贵(在我希望加载非常大的图像或列表非常长的情况下),但
和
利用React.memo
,但前者根本不会改变重新渲染行为,而后者使应用程序的行为非常怪异,您可以尝试用其中一个替换
,以查看效果。我还尝试在onClick
上使用onClick回调
,但也没有帮助
我是否错误地使用了React.memo
或React.useCallBack
?我能做些什么来满足需求?多谢各位
如果代码链接过期,请将代码粘贴到下面:
import React,{memo,useffect,useState}来自“React”;
从“react native”导入{SafeAreaView,FlatList,StyleSheet};
从“expo常量”导入常量;
从“不可变”导入{Set};
从“react native elements”导入{Button,ListItem};
从“axios”导入axios;
常量项=({id,title,avatarUrl,selected,onClick})=>{
log(`rendering item id=${id},selected=${selected}`);
返回(
onClick(id)}
/>
);
};
功能项EQ(上一项,下一项){
返回previitem.id==nextItem.id&&previitem.selected==nextItem.selected;
}
//没有区别,每次单击一行时,所有行都会重新呈现
const MemoizedItem=备忘录(项目);
//做一些改变,但行为看起来很奇怪。尝试单击周围并查看日志
const MemoizedItem2=备忘录(项目,项目等式);
常量项=({data,selectedItems,onClick})=>{
console.log(“呈现项”);
//替换为或看到效果
常量_renderItem=({item})=>(
);
返回(
项目.电子邮件}
extraData={selectedItems}
/>
);
};
常量应用=()=>{
const[items,setItems]=useState([]);
const[selectedItems,setSelectedItems]=useState(Set());
useffect(()=>{
const fetchData=async()=>{
log(“获取数据”);
//读回5个随机用户
//每个用户都是这样的:
// {
//“性别”:“男性”,
//“姓名”:{
//“头衔”:“先生”,
//“第一”:“哈雷”,
//“最后”:“张”
// },
//“地点”:{
//“街道”:{
//“数字”:6470,
//“名称”:“巴克利路”
// },
//“城市”:“北帕默斯顿”,
//“州”:“Manawatu Wanganui”,
//“国家”:“新西兰”,
//“邮政编码”:90911,
//“坐标”:{
//“纬度”:“66.2907”,
//“经度”:“-18.0881”
// },
//“时区”:{
//“偏移量”:“+8:00”,
//“描述”:“北京、珀斯、新加坡、香港”
// }
// },
//“电子邮件”:“哈雷。zhang@example.com",
//“登录”:{
//“uuid”:“6fda195e-3e63-476c-84d0-7c577c7b74f9”,
//“用户名”:“smallbear541”,
//“密码”:“daisy1”,
//“盐”:“p6AmByUq”,
//“md5”:“0358f2385a9936369adc89b9233f037b”,
//“sha1”:“8decc817cf32ca6e58814502bb3e54152208c5b5”,
//“sha256”:“96FF7627348250646EDD3238504271840A0CB6AAAC293782F7EEC1A6F884C07”
// },
//“dob”:{
//“日期”:“1987-12-07T13:00:15.244Z”,
//“年龄”:33
// },
//“注册”:{
//“日期”:“2008-01-23T19:33:01.672Z”,
//“年龄”:12岁
// },
//“电话”:(474)-743-9612,
//“单元格”:(539)-021-1315“,
//“id”:{
//“名称”:“,
//“值”:空
// },
//“图片”:{
//“大”:https://randomuser.me/api/portraits/men/49.jpg",
//“中等”:https://randomuser.me/api/portraits/med/men/49.jpg",
//“缩略图”:https://randomuser.me/api/portraits/thumb/men/49.jpg"
// },
//“nat”:“新西兰”
// }
常量结果=等待axios(“https://randomuser.me/api/?results=5");
设置项(结果、数据、结果);
};
fetchData();
}, []);
const onClick=id=>{
const newSelectedItems=selectedItems.has(id)
?选择编辑项。删除(id)
:selectedItems.add(id);
log(`selected items=${JSON.stringify(selectedItems,null,2)}`);
console.log(
`新选定项=${JSON.stringify(newSelectedItems,null,2)}`
);
设置selecteditems(newSelectedItems);
}
//无济于事
const onClickUseCallBack=React.useCallback(
id=>{
const newSelectedItems=selectedItems.has(id)
?选择编辑项。删除(id)
:selectedItems.add(id);
log(`selected items=${JSON.stringify(selectedItems,null,2)}`);
console.log(
`新选定项=${JSON.stringify(newSelectedItems,null,2)}`
);
设置selecteditems(newSelectedItems);
},
[selectedItems]
);
返回(
console.log(`Printing selected items${selectedItems}`)}
/>
);
};
导出默认应用程序;
const styles=StyleSheet.create({
容器:{
弹性:1,
marginTop:Constants.statusBarHeight,
marginHorizontal:16
},
项目:{
背景颜色:“f9c2ff”,
填充:20,
利润率:8
}
});
expo package.json
{
"main": "node_modules/expo/AppEntry.js",
"scripts": {
"start": "expo start",
"android": "expo start --android",
"ios": "expo start --ios",
"web": "expo start --web",
"eject": "expo eject"
},
"dependencies": {
"axios": "^0.19.2",
"expo": "~36.0.0",
"immutable": "^4.0.0-rc.12",
"react": "~16.9.0",
"react-dom": "~16.9.0",
"react-native": "https://github.com/expo/react-native/archive/sdk-36.0.0.tar.gz",
"react-native-elements": "^1.2.7",
"react-native-web": "~0.11.7"
},
"devDependencies": {
"@babel/core": "^7.0.0",
"babel-preset-expo": "~8.0.0"
},
"private": true
}
MomoizedItem
+onClickUseCallBack
是一个良好的开端
重新渲染
const onClickUseCallBack = React.useCallback(
id => {
setSelectedItems((selectedItems) => {
const newSelectedItems = selectedItems.has(id)
? selectedItems.delete(id)
: selectedItems.add(id);
return newSelectedItems
});
},
[]
);
import React, { memo, useEffect, useState } from "react";
import { SafeAreaView, FlatList, StyleSheet } from "react-native";
import Constants from "expo-constants";
import { Set } from "immutable";
import { Button, ListItem } from "react-native-elements";
import axios from "axios";
const Item = ({ id, title, avatarUrl, selected, onClick }) => {
console.log(`rendering item id=${id}, selected=${selected}`);
return (
<ListItem
title={title}
leftAvatar={{ source: { uri: avatarUrl } }}
containerStyle={[
styles.item,
{ backgroundColor: selected ? "#6e3b6e" : "#f9c2ff" }
]}
underlayColor="transparent"
onPress={() => onClick(id)}
/>
);
};
function itemEq(prevItem, nextItem) {
return prevItem.id === nextItem.id && prevItem.selected === nextItem.selected;
}
// Does not make a difference, every time a row is clicked, all rows are re-rendered
const MemoizedItem = memo(Item);
// Make some difference but the behavior looks very weird. Try click around and see the log
const MemoizedItem2 = memo(Item, itemEq);
const Items = ({ data, selectedItems, onClick }) => {
console.log("rendering items");
// Replace <Item /> with <MemoizedItem /> or <MemoizedItem2 /> to see effect
const _renderItem = ({ item }) => (
<MemoizedItem
id={item.email}
title={`${item.name.title} ${item.name.first} ${item.name.last}`}
avatarUrl={item.picture.thumbnail}
selected={selectedItems.has(item.email)}
onClick={onClick}
/>
);
return (
<FlatList
data={data}
renderItem={_renderItem}
keyExtractor={item => item.email}
extraData={selectedItems}
/>
);
};
const App = () => {
const [items, setItems] = useState([]);
const [selectedItems, setSelectedItems] = useState(Set());
useEffect(() => {
const fetchData = async () => {
console.log("fetching data");
// Read 5 random users back
// Each user is like this:
// {
// "gender":"male",
// "name":{
// "title":"Mr",
// "first":"Harley",
// "last":"Zhang"
// },
// "location":{
// "street":{
// "number":6470,
// "name":"Buckleys Road"
// },
// "city":"Palmerston North",
// "state":"Manawatu-Wanganui",
// "country":"New Zealand",
// "postcode":90911,
// "coordinates":{
// "latitude":"66.2907",
// "longitude":"-18.0881"
// },
// "timezone":{
// "offset":"+8:00",
// "description":"Beijing, Perth, Singapore, Hong Kong"
// }
// },
// "email":"harley.zhang@example.com",
// "login":{
// "uuid":"6fda195e-3e63-476c-84d0-7c577c7b74f9",
// "username":"smallbear541",
// "password":"daisy1",
// "salt":"p6AmByUq",
// "md5":"0358f2385a9936369adc89b9233f037b",
// "sha1":"8decc817cf32ca6e58814502bb3e54152208c5b5",
// "sha256":"96ff7627348250646edd31238504271840a0cb6aaac293782f7eec1a6f884c07"
// },
// "dob":{
// "date":"1987-12-07T13:00:15.244Z",
// "age":33
// },
// "registered":{
// "date":"2008-01-23T19:33:01.672Z",
// "age":12
// },
// "phone":"(474)-743-9612",
// "cell":"(539)-021-1315",
// "id":{
// "name":"",
// "value":null
// },
// "picture":{
// "large":"https://randomuser.me/api/portraits/men/49.jpg",
// "medium":"https://randomuser.me/api/portraits/med/men/49.jpg",
// "thumbnail":"https://randomuser.me/api/portraits/thumb/men/49.jpg"
// },
// "nat":"NZ"
// }
const results = await axios("https://randomuser.me/api/?results=5");
setItems(results.data.results);
};
fetchData();
}, []);
// Does not help
const onClickUseCallBack = React.useCallback(
id => {
setSelectedItems((selectedItems) => {
const newSelectedItems = selectedItems.has(id)
? selectedItems.delete(id)
: selectedItems.add(id);
return newSelectedItems
});
},
[]
);
return (
<SafeAreaView style={styles.container}>
<Items data={items} selectedItems={selectedItems} onClick={onClickUseCallBack} />
<Button
title="Print"
onPress={() => console.log(`Printing selected items ${selectedItems}`)}
/>
</SafeAreaView>
);
};
export default App;
const styles = StyleSheet.create({
container: {
flex: 1,
marginTop: Constants.statusBarHeight,
marginHorizontal: 16
},
item: {
backgroundColor: "#f9c2ff",
padding: 20,
marginVertical: 8
}
});