Javascript 反应本机奇数行为以呈现平面列表
我的目标是一次性渲染20个项目,而不是渲染10个项目,并在600毫秒后重新渲染20个项目 我确保只在抓取完成后渲染平面列表。我依赖于Javascript 反应本机奇数行为以呈现平面列表,javascript,react-native,react-native-android,jsx,Javascript,React Native,React Native Android,Jsx,我的目标是一次性渲染20个项目,而不是渲染10个项目,并在600毫秒后重新渲染20个项目 我确保只在抓取完成后渲染平面列表。我依赖于React。使用effect和数据依赖项重新渲染,以模拟效果在向下滚动时加载更多。行为是相同的,向下滚动时,它会重新渲染整个平面列表,并每10个项目重新渲染一次 console.log [Tue Sep 15 2020 08:31:56.797] LOG Album() useEffect() [Tue Sep 15 2020 08:31:57.510]
React。使用effect
和数据
依赖项重新渲染,以模拟效果在向下滚动时加载更多。行为是相同的,向下滚动时,它会重新渲染整个平面列表,并每10个项目重新渲染一次
console.log
[Tue Sep 15 2020 08:31:56.797] LOG Album() useEffect()
[Tue Sep 15 2020 08:31:57.510] LOG Album() renderItem() render 1
[Tue Sep 15 2020 08:31:57.651] LOG Album() renderItem() render 2
[Tue Sep 15 2020 08:31:57.758] LOG Album() renderItem() render 3
[Tue Sep 15 2020 08:31:57.851] LOG Album() renderItem() render 4
[Tue Sep 15 2020 08:31:58.700] LOG Album() renderItem() render 5
[Tue Sep 15 2020 08:31:58.175] LOG Album() renderItem() render 6
[Tue Sep 15 2020 08:31:58.272] LOG Album() renderItem() render 7
[Tue Sep 15 2020 08:31:58.375] LOG Album() renderItem() render 8
[Tue Sep 15 2020 08:31:58.525] LOG Album() renderItem() render 9
[Tue Sep 15 2020 08:31:58.654] LOG Album() renderItem() render 10
[Tue Sep 15 2020 08:32:04.758] LOG Album() renderItem() render 1
[Tue Sep 15 2020 08:32:04.940] LOG Album() renderItem() render 2
[Tue Sep 15 2020 08:32:05.106] LOG Album() renderItem() render 3
[Tue Sep 15 2020 08:32:05.240] LOG Album() renderItem() render 4
[Tue Sep 15 2020 08:32:05.420] LOG Album() renderItem() render 5
[Tue Sep 15 2020 08:32:05.530] LOG Album() renderItem() render 6
[Tue Sep 15 2020 08:32:05.608] LOG Album() renderItem() render 7
[Tue Sep 15 2020 08:32:05.737] LOG Album() renderItem() render 8
[Tue Sep 15 2020 08:32:05.885] LOG Album() renderItem() render 9
[Tue Sep 15 2020 08:32:05.986] LOG Album() renderItem() render 10
[Tue Sep 15 2020 08:32:06.310] LOG Album() renderItem() render 11
[Tue Sep 15 2020 08:32:06.920] LOG Album() renderItem() render 12
[Tue Sep 15 2020 08:32:06.148] LOG Album() renderItem() render 13
[Tue Sep 15 2020 08:32:06.201] LOG Album() renderItem() render 14
[Tue Sep 15 2020 08:32:06.280] LOG Album() renderItem() render 15
[Tue Sep 15 2020 08:32:06.340] LOG Album() renderItem() render 16
[Tue Sep 15 2020 08:32:06.414] LOG Album() renderItem() render 17
[Tue Sep 15 2020 08:32:06.457] LOG Album() renderItem() render 18
[Tue Sep 15 2020 08:32:06.521] LOG Album() renderItem() render 19
[Tue Sep 15 2020 08:32:06.589] LOG Album() renderItem() render 20
./src/features/Album/index.js
import React from 'react';
import {
StyleSheet,
ActivityIndicator,
SafeAreaView,
View,
TouchableOpacity,
Text,
FlatList,
RefreshControl,
Animated,
} from 'react-native';
import Swipeable from 'react-native-gesture-handler/Swipeable';
const styles = StyleSheet.create({
item: {
paddingVertical: 20,
paddingHorizontal: 10,
},
separator: {
flex: 1,
height: 1,
backgroundColor: '#e4e4e4',
marginLeft: 10,
},
leftActions: {
backgroundColor: '#388e3c',
justifyContent: 'center',
flex: 1, // continue to swipe.
},
actionText: {
color: '#fff',
fontWeight: '600',
padding: 20,
},
rightActions: {
backgroundColor: '#dd2c00',
justifyContent: 'center',
// flex: 1, // continue to swipe.
alignItems: 'flex-end',
},
});
function LeftActions(progress, dragX) {
// console.log('Album() LeftActions()', progress, dragX)
const scale = dragX.interpolate({
inputRange: [0, 100],
outputRange: [0, 1],
extrapolate: 'clamp',
});
return (
<View style={styles.leftActions}>
<Animated.Text style={[styles.actionText, {transform: [{scale}]}]}>
Add to Cart
</Animated.Text>
</View>
);
}
function RightActions({progress, dragX, onPress}) {
// console.log('Album() LeftActions()', progress, dragX)
const scale = dragX.interpolate({
inputRange: [-100, 0],
outputRange: [1, 0],
extrapolate: 'clamp',
});
return (
<TouchableOpacity onPress={onPress}>
<View style={styles.rightActions}>
<Animated.Text style={[styles.actionText, {transform: [{scale}]}]}>
Delete
</Animated.Text>
</View>
</TouchableOpacity>
);
}
function Item({item, onSwipeFromLeft, onRightPress}) {
// console.log('Album() Item() render')
return (
<Swipeable
renderLeftActions={LeftActions}
onSwipeableLeftOpen={onSwipeFromLeft}
renderRightActions={(progress, dragX) => <RightActions progress={progress} dragX={dragX} onPress={onRightPress} />}
>
<View style={[styles.item]}>
<Text>{`${item.id} ${item.title}`}</Text>
</View>
</Swipeable>
);
}
function Separator() {
return <View style={styles.separator} />;
}
export default function Album() {
const [isLoading, setLoading] = React.useState(true);
const [currentPage, setCurrentPage] = React.useState(1);
// const [itemPerPage, setItemPerPage] = React.useState(20);
const itemPerPage = 20;
const [data, setData] = React.useState([]);
const [error, setError] = React.useState();
React.useEffect(() => {
console.log('Album() useEffect()');
fetch(
`http://jsonplaceholder.typicode.com/albums?_start=${
currentPage * itemPerPage - itemPerPage
}&_limit=${itemPerPage}`,
)
.then((response) => response.json())
.then((json) => setData((initial) => [...initial, ...json]))
.catch((e) => setError(e))
.finally(() => setLoading(false));
}, [currentPage]);
// console.log('Album()', data);
// question: VirtualizedList: You have a large list that is slow to update - make sure your renderItem function renders components that follow React performance best practices like PureComponent, shouldComponentUpdate, etc. {"contentLength": 3179.666748046875, "dt": 627, "prevDt": 658}
const memo = React.useMemo(() => renderItem, [data]);
function renderItem({item}) {
console.log('Album() renderItem() render', item.id);
return (
<Item
item={item}
onSwipeFromLeft={() => alert('swiped from the left')}
onRightPress={() => alert('pressed right')}
/>
);
}
function handleRefresh() {
console.log('Album() handleRefresh()');
setLoading(true);
// simulate fetch
setTimeout(() => {
setLoading(false);
}, 1000);
}
function handleLoadMore() {
// fake limitPage
if (100 / itemPerPage === currentPage) return;
console.log('Album() handleLoadMore()');
setCurrentPage((page) => page + 1);
}
return (
<>
{isLoading ? (
<ActivityIndicator />
) : (
<>
{error && <Text>{error}</Text>}
<Text>Album</Text>
<SafeAreaView>
<FlatList
data={data}
// Is this parameter bad for performance? Put it into perspective, it renders 1,5x more if this parameter is set to half.
// initialNumToRender={itemPerPage / 2}
renderItem={memo}
keyExtractor={(item) =>
'_' + Math.random().toString(36).substr(2, 9) + item.id
}
refreshControl={
<RefreshControl
refreshing={isLoading}
onRefresh={handleRefresh}
/>
}
onEndReachedThreshold={0.1}
onEndReached={handleLoadMore}
ItemSeparatorComponent={Separator}
/>
</SafeAreaView>
</>
)}
</>
);
}
从“React”导入React;
进口{
样式表,
活动指示器,
安全区域视图,
看法
可触摸不透明度,
文本,
平面列表,
刷新控制,
有生气的
}从“反应本机”;
从“反应本机手势处理程序/Swipeable”导入Swipeable;
const styles=StyleSheet.create({
项目:{
填充垂直:20,
水平方向:10,
},
分离器:{
弹性:1,
身高:1,,
背景颜色:“#e4”,
边缘左:10,
},
leftActions:{
背景颜色:“#388e3c”,
为内容辩护:“中心”,
flex:1,//继续刷卡。
},
行动文本:{
颜色:“#fff”,
重量:'600',
填充:20,
},
权利行动:{
背景颜色:“#dd2c00”,
为内容辩护:“中心”,
//flex:1,//继续刷卡。
对齐项目:“柔性端”,
},
});
函数LeftActions(进度、dragX){
//log('Album()LeftActions()',progress,dragX)
常量比例=dragX.interpolate({
输入范围:[01100],
outputRange:[0,1],
外推:“夹具”,
});
返回(
添加到购物车
);
}
函数RightActions({progress,dragX,onPress}){
//log('Album()LeftActions()',progress,dragX)
常量比例=dragX.interpolate({
输入范围:[-100,0],
outputRange:[1,0],
外推:“夹具”,
});
返回(
删除
);
}
函数项({Item,onsweepfromleft,onRightPress}){
//log('Album()Item()render')
返回(
}
>
{`${item.id}${item.title}`}
);
}
函数分隔符(){
返回;
}
导出默认函数相册(){
const[isLoading,setLoading]=React.useState(true);
const[currentPage,setCurrentPage]=React.useState(1);
//const[itemPerPage,setItemPerPage]=React.useState(20);
const itemPerPage=20;
const[data,setData]=React.useState([]);
const[error,setError]=React.useState();
React.useffect(()=>{
log('Album()useffect()');
取回(
`http://jsonplaceholder.typicode.com/albums?_start=${
currentPage*itemPerPage-itemPerPage
}&_limit=${itemPerPage}`,
)
.then((response)=>response.json())
.然后((json)=>setData((初始)=>[…初始,…json]))
.catch((e)=>setError(e))
.最后(()=>setLoading(false));
},[currentPage]);
//log('Album()',data);
//问题:VirtualizedList:您有一个更新缓慢的大型列表-请确保您的renderItem函数呈现符合React性能最佳实践的组件,如PureComponent、shouldComponentUpdate等。{“contentLength”:3179.666748046875,“dt”:627,“prevDt”:658}
const memo=React.usemo(()=>renderItem[data]);
函数renderItem({item}){
log('Album()renderItem()render',item.id);
返回(
警报('从左边刷卡')}
onRightPress={()=>警报('pressed right')}
/>
);
}
函数handleRefresh(){
log('Album()handleRefresh()');
设置加载(真);
//模拟提取
设置超时(()=>{
设置加载(假);
}, 1000);
}
函数handleLoadMore(){
//假网页
如果(100/itemPerPage==currentPage)返回;
log('Album()handleLoadMore()');
setCurrentPage((第页)=>第+1页);
}
返回(
{孤岛加载(
) : (
{error&&{error}
专辑
'.'+Math.random().toString(36).substr(2,9)+item.id
}
刷新控制={
}
onEndReachedThreshold={0.1}
onEndReached={handleLoadMore}
ItemSeparatorComponent={Separator}
/>
)}
);
}
平面列表就是这样工作的
Flatlist构建在虚拟化列表的基础上,它只渲染屏幕上可见的项目,并在滚动条上显示,它将自动删除/卸载屏幕外的项目,从而提供处理大型列表的优化方法
但是在您的情况下,如果它总是20,您可以尝试设置initialNumToRender
,并且大部分情况下这应该是可行的
进一步阅读