Created
May 22, 2020 16:47
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Better performance paginated FlatList
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import React, { useState, useEffect } from 'react'; | |
import { Text, FlatList, View, TextInput, TouchableOpacity } from 'react-native'; | |
let arr: any[] = []; | |
for (let i = 1; i <= 100; i++) { | |
arr.push({ id: i, text: `mensagem bacana #${i}` }); | |
} | |
arr.reverse(); | |
const api = { | |
fetchMessages(page: number = 1): Promise<any[]> { | |
return new Promise((resolve) => { | |
setTimeout(() => { | |
resolve(arr.slice(20 * (page - 1), 20 * page)); | |
}, 1000); | |
}); | |
}, | |
}; | |
const Message: React.FC<any> = ({ text }) => { | |
return ( | |
<View style={{ padding: 10, backgroundColor: '#ffffff', elevation: 2, marginBottom: 10 }}> | |
<Text>{text}</Text> | |
</View> | |
); | |
}; | |
const Main: React.FC = () => { | |
const [messages, setMessages] = useState<any[]>([]); | |
const [currentPage, setCurrentPage] = useState(1); | |
const [totalPages, setTotalPages] = useState(0); | |
const [text, setText] = useState<string>(''); | |
const [fetching, setFetching] = useState(false); | |
const [onEndReachedCalledDuringMomentum, setOnEndReachedCalledDuringMomentum] = useState(true); | |
useEffect(() => { | |
async function fetchMessages(page = 1) { | |
console.log('called fetchmessages', page); | |
setFetching(true); | |
const response = await api.fetchMessages(page); | |
setTotalPages(5); | |
// setMessages((data) => [...data, ...response]); | |
setMessages((data) => { | |
const items = [...data, ...response]; | |
const uniqueIds = [...new Set(items.map((item) => item.id))]; | |
return uniqueIds.map((id) => items.find((item) => item.id === id)); | |
}); | |
setFetching(false); | |
} | |
fetchMessages(currentPage); | |
const interval = setInterval(fetchMessages, 5000); | |
return () => clearInterval(interval); | |
}, [currentPage]); | |
function handleAddMessage() { | |
setMessages([{ id: Date.now(), text }, ...messages]); | |
setText(''); | |
} | |
function goToNextPage() { | |
if (!onEndReachedCalledDuringMomentum) { | |
if (fetching || (totalPages > 0 && currentPage >= totalPages)) { | |
return; | |
} | |
console.log('called gotonextpage', currentPage); | |
setCurrentPage((data) => data + 1); | |
setOnEndReachedCalledDuringMomentum(true); | |
} | |
} | |
return ( | |
<> | |
<FlatList | |
data={messages} | |
keyExtractor={(item) => String(item.id)} | |
renderItem={({ item }) => <Message text={item.text} />} | |
inverted={true} | |
onEndReached={goToNextPage} | |
onEndReachedThreshold={0.25} | |
onMomentumScrollBegin={() => setOnEndReachedCalledDuringMomentum(false)} | |
/> | |
<View style={{ flexDirection: 'row', alignItems: 'center' }}> | |
<TextInput | |
value={text} | |
onChangeText={setText} | |
placeholder="Digite sua mensagem" | |
style={{ flex: 1, height: 50, borderWidth: 1, borderColor: 'lightseagreen' }} | |
/> | |
<TouchableOpacity | |
style={{ | |
justifyContent: 'center', | |
height: 50, | |
padding: 10, | |
borderWidth: 1, | |
borderColor: 'lightseagreen', | |
backgroundColor: 'lightseagreen', | |
}} | |
onPress={handleAddMessage}> | |
<Text style={{ fontWeight: 'bold', color: '#ffffff' }}>Enviar</Text> | |
</TouchableOpacity> | |
</View> | |
</> | |
); | |
}; | |
export default Main; |
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