FlatList rendering is heavy for big data set - reactjs

In my application I have a FlatList with dataset of 100 items in it. Each item has a complex UI and I noticed that it's taking a heavy toll on performance. The page that has the list takes up to 5 seconds to load.
I noticed that the moment the component is rendered for the first time, the renderItem function of the FlatList is also called for each and every item in my data set, I also noticed that it also happens if there any other setState change for other stuff on that page. Is there a way to prevent this re-rendering of the flat list or at least to re-render only the visible items - just like with Recycle with in native Android?
How can I only render the visible items when the component first appears?
I tried to use initialNumToRender and maxToRenderPerBatch but neither have worked.
Here is an example of the code:
const Item = ({ title }) => (
<View style={styles.item}>
<Text style={styles.title}>{title}</Text>
</View>
);
const App = () => {
const [text, setText] = React.useState('')
const renderItem = ({ item }) => {
console.log("Render Item")
return (<Item title={item.title} />)
};
return (
<SafeAreaView style={styles.container}>
<TextInput
value={text}
onChangeText={(val) => setText(val)}
/>
<FlatList
data={DATA}
renderItem={renderItem}
keyExtractor={item => item.id}
initialNumToRender={6}
maxToRenderPerBatch={6}
/>
</SafeAreaView>
);
}
If I try to type something in TextInput the whole list re-renders but nothing in the list has changed.. how can I prevent this?

Related

React Native FlatList: how to reset scroll position

I have a horizontal FlatList in my React Native iOS app. At the bottom of the screen, the FlatList is displayed with 5 items. If you click on the last item (scrolled all the way to the right), the screen will refresh and the FlatList will remain scrolled to the right. How can I get the FlatList to always reset the scroll position (to scroll from the beginning) when the screen changes?
Edit: I have a feeling that my screen is not actually "refreshing" but rather merely changing the data shown on the screen. In this case I may need to trigger a refresh of the screen somehow to cause the FlatList to reset the scroll position? Any help would be greatly appreciated!
const HorizontalScroll = ({items, handlePress}) => {
const renderItem = ({item}) => {
const itemData = { color: item.color, title: item.title };
return <HorizontalItem itemData={itemData} handlePress={handlePress} />;
};
return (
<View style={styles.container}>
<FlatList
data={items}
renderItem={renderItem}
horizontal={true}
numColumns={1}
key={(item) => item.id}
initialNumToRender={5}
scrollToIndex={0}
ItemSeparatorComponent={() => <View style={{width: 8}} />}>
</FlatList>
</View>
);
};
I solved this problem by forcing a refresh of the component. Specifically, I added a key prop to my component so that every time the key value changes, it remounts the component. This causes the FlatList to reset the scroll position to the beginning.
<View key={items[0].title}>
{content}
</View>

FlatList, Props ListHeaderComponent and Dynamic flatlist data

Sorry for the title, I wasn't inspired, and I didn't know what title to put for my problem.
I'm using Socket.io on my React native application to render some dynamics datas.
I'm using FlatList to display all this datas, and I need to show some contents like filters and buttons at the top of the FlatList.
So In my FlatList Props, I used ListHeaderComponent and in this component I display one other flatlist and contents.
My problem is :
When the main FlatList is updated with one of the Socket.io response (Every 5sec), all the components displayed by ListHeaderComponent aren't usable for a bit of time.
This period is like 500ms or less, but in the ListHeaderComponent I have some buttons / filters, and they are not clickable during this period.
And the problem is repeated each time the FlatList data is updated.
You can see my code (simplyfied) here :
export default function MyList({ navigation }) {
const [myData, setMyData] = useState<ResponseType[]>([])
// Socket Io
const socket = io(SOCKET_URL, { forceNew: true, timeout: 5000 })
useEffect(() => {
socket.on("connect", () => {
console.log("Connected to Socket ID : ", socket.id)
})
return () => {
socket.disconnect()
socket.close()
}
},[])
socket.on("socketResponse", (data: ResponseType) => {
setMyData(prevDate => [...prevDate, data])
})
const renderFilterItem = ({ item }: { item: Filter }) => <Text key={ item.id }>{ item.title }</Text>
const renderListItem = ({ item }: { item: ResponseType }) => <Text key={ item.id }>{ item.id }</Text>
const ListTop = () => (
<>
<TouchableOpacity onPress={() => navigation.navigate('HomePage')}>
<Text>BACK CONTENT</Text>
</TouchableOpacity>
<FlatList
horizontal
showsHorizontalScrollIndicator={false}
data={someFilters}
keyExtractor={(item) => item.id}
renderItem={renderFilterItem}
/>
</>
)
return (
<FlatList
ListHeaderComponent={ListTop}
data={myData}
keyExtractor={(item) => item.id}
renderItem={renderListItem}
maxToRenderPerBatch={5}
windowSize={2}
/>
)
}
I don't know how to explain better my problem. But If I move the component of ListHeaderComponent above the FlatList, there is no more problem.
But If I do this, just the FlatList is scrollable, and I want all the page scrollable.
I can't wrap my Flatlist with a ScrollView because of this error : VirtualizedLists should never be nested inside plain ScrollViews with the same orientation
Has anyone faced this problem ?
Thanks
try to use optimization for ListTop component as a possible problem here would be rendering of your functional component due to change of parent one.
here is the code sample.
import React, {useCallback} from 'react';
// your other codes
const ListTop = useCallback(() => (
<>
<TouchableOpacity onPress={() => navigation.navigate('HomePage')}>
<Text>BACK CONTENT</Text>
</TouchableOpacity>
<FlatList
horizontal
showsHorizontalScrollIndicator={false}
data={someFilters}
keyExtractor={(item) => item.id}
renderItem={renderFilterItem}
/>
</>
), [someFilters]);
here the component will be memoized until there is no change in someFilters.

React Native - passing data model from Flat list

I have a FlatList:
<ScrollView nestedScrollEnabled={true}>
<Screen style={styles.screen}>
<TouchableOpacity onPress={() => navigation.navigate("ProfileDetailScreen")}>
<FlatList
data={users}
renderItem={renderItem}
keyExtractor={item => item.uid}
/>
</TouchableOpacity>
</Screen>
</ScrollView>
And Im getting some data from firebase like:
useEffect(() => {
firebaseUsers
.onSnapshot(
querySnapshot => {
const newUsers = []
querySnapshot.forEach(doc => {
const user = doc.data()
user.id = doc.id
newUsers.push(user)
});
setUsers(newUsers)
},
error => {
console.log(error)
}
)
}, [])
The data I get from firebase has name, image and age (and more more fields).
How can I pass all the data for a single user into the ProfileDetailedScreen?
Not sure the correct way to achieve this (not sure If I need to create data models etc?)
I don't know firebase that well but I have experience in RN. From what I'm understanding, you're going to want to make the renderItem function in your FlatList a function that returns a TouchableOpacity with navigation to the ProfileDetailedScreen component while also passing the user object. You'll display the user details in the ProfileDetailedScreen.
Passing items in navigation documentation
/* 'item' is a user from the users array you passed into the data property of your FlatList above */
renderItem = ({item}) => (
<TouchableOpacity onPress={() => navigation.navigate("ProfileDetailScreen", item)}>
<Text> item?.name </Text> {/* show brief info about user */}
</TouchableOpacity>
)
If you're using Redux for your application state, you could also navigate only to "ProfileDetailScreen" and dispatch an action that sets a currentUser in state. Your "ProfileDetailsScreen" would then pull the currentUser from state. This way has more moving parts but the component piece would look something like this:
/* 'item' is a user from the users array you passed into the data property in your FlatList above */
renderItem = ({item}) => (
<TouchableOpacity onPress={this.setUserAndNavigate.bind(this, item)}>
<Text> item?.name </Text> {/* show brief info about user */}
</TouchableOpacity>
)
setUserAndNavigate = (user) => {
this.props.setUser(user);
navigation.navigate("ProfileDetailScreen");
}

onPress of TouchableOpacity gets called when loading Flatlist

I have a flatlist with a search function. In the next step, I want something to happen when I press within the item. I'm facing the problem that the TouchableOpacity is visible, but nothing happens when it's pressed. I've tried the same with a Button and face the same issue.
Instead of onPress being called when something is pressed, it somehow get's called once the screen loads immediately. If I for example console.log(item.title) I get all the titles in my console log that are currently in the flatlist.
I've tried to figure out what is causing this for many hours, but can't seem to find any reason. Any help is highly appreciated.
I have a Flatlist that is populated with data, set up as follows:
return (
<View style={styles.list}>
<FlatList
data = {this.state.data}
renderItem={renderListItem}
keyExtractor={item => item.id}
ListHeaderComponent={this.renderHeader}
/>
</View>
);
}
}
const renderListItem = (item) => {
return (
<MyTouchable
id={item.item.id}
title={item.item.title}
/>
);
}
MyTouchable Component looks like this:
<View>
<TouchableOpacity onPress={console.log("Pressed")}>
<View style={styles.mainView}>
<View>
<Text style={styles.text}>{props.id} {props.title}</Text>
</View>
</View>
</TouchableOpacity>
</View>
Try to pass the console.log inside an arrow function
<TouchableOpacity onPress={() => console.log("Pressed")}>
...
</TouchableOpacity>
You can’t write like this: <Component makeThing={myFunc()} />. You should write like that: <Component makeThing={() => myFunc()} /> if you are not using useCallback.
Make sure to read the docs about passing functions to components.
You must provide and arrow function, and call your function inside it.
Or just use useCallback hook:
const Component = () => {
const myFunction = useCallback(() => {
// do something
}, []);
return <AnotherComponent coolFunction={myFunction} />
}

Function inside a FlatList item does not fire when passing the renderItem as prop to the component

Somehow the onPress event is not fired when pressing on a list item inside a FlatList component. I have a main component that uses a Autocomplete component. This Autocomplete component consists of a TextInput and FlatList within a View:
//Autocomplete component
//...
return (
<View>
<TextInput
value={props.value}
onChangeText={props.onChangeText}
onFocus={props.onFocus}
onBlur={props.onBlur}
/>
<FlatList
data={props.data}
keyExtractor={item => item.id}
renderItem={props.renderItem}/>
</View>
)
The main component passes a renderItem prop to the Autocomplete component, in which I want to call a function when pressing an item on the list:
//main component
//...
const selectHandler = (item) => {
console.log("test")
};
return(
<Autocomplete
data={filteredData}
value={searchTerm}
renderItem={itemData => (
<TouchableOpacity
onPress={(item) => selectHandler(item)}>
<Text>
some text
</Text>
</TouchableOpacity >
)}
onChangeText={text => setSearchTerm(text)}
onFocus={focusHandler}
onBlur={blurHandler}
/>
)
However, this console.log("test") never fires. What might be the reason for this?
Try renderItem={() => props.renderItem}/> in the FlatList.
I found the reason. Because the keyboard is open when using the TextInput I need to add keyboardShouldPersistTaps={'handled'} to the FlatList component. I did not see that I have to click twice initially, because my Autocomplete component disappears onBlur and I thought that the onPress event did not work at all.

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