I'm working on a flatlist that has complex child that cause expensive rerender, I need to optimize that but I'm not able to stop the rerendering with useMemo, please help me to go through this.
Here my list code:
<FlatList
data={thePosts}
extraData={thePosts}
keyExtractor={(item, index) => index.toString()}
removeClippedSubviews={true}
maxToRenderPerBatch={5}
updateCellsBatchingPeriod={30}
initialNumToRender={11}
windowSize={5}
refreshing={isRefreshing}
onRefresh={handleOnRefresh}
onEndReached={isLoading ? () => null : () => getPosts("more")}
onEndReachedThreshold={0.1}
renderItem={memoizedPost}
//renderItem={renderThePost}
ItemSeparatorComponent={renderThePostSep}
ListFooterComponent={renderThePostListFooter}
/>
here the renderPost:
const renderThePost = (props) => {
let post = props.item;
if (post[0].type == "share") {
return (
<TheSharedPost thePost={post} />
);
} else {
return <ThePost thePost={post} />;
}
};
I've tried to use memoization like this:
const memoizedPost = useMemo(() => renderThePost, []);
Now the problem is, the empty array as useMemo argument I think that only accept the first render but not working, I've tried to use [item.someProperty] but I'm not able to recognize item in the argument (item is not defined)
I've also used useCallback but still no luck, a lot o rerendering happen. Please help me to fix this. Tnz
you can use React.memo to avoid rendering of flatlist items
function TheSharedPost(props) {
/* render using props */
}
export default React.memo(TheSharedPost);
function ThePost(props) {
/* render using props */
}
export default React.memo(ThePost);
Related
I am using react-native-snap-carousel to swipe through images. When there is like 0-10 images it's working fine, but otherwise it's very laggy. I tried the optimization methods but didn't fix it.
Here is my implementation (selectedItems is the data I have):
const renderItem = useCallback(
({ item, index }) => {
return (
<CarouselImage
ad={ad}
item={item}
index={index}
showImage={showImage}
/>
);
},
[ad, showImage]);
return ad?.videos?.length > 0 || ad?.images?.length > 0 ? (
<View style={styles.container}>
<Carousel
initialNumToRender={selectedItems.length}
maxToRenderPerBatch={5}
ref={carouselRef}
swipeThreshold={5}
itemWidth={wp(375)}
data={selectedItems}
sliderWidth={wp(375)}
enableMomentum={false}
lockScrollWhileSnapping
renderItem={renderItem}
onSnapToItem={(index) => setActiveSlide(index)}
/>
<Pagination
activeOpacity={1}
tappableDots={true}
animatedDuration={100}
inactiveDotScale={0.4}
inactiveDotOpacity={0.4}
carouselRef={carouselRef}
dotStyle={styles.dotStyle}
activeDotIndex={activeSlide}
dotsLength={selectedItems.length}
containerStyle={styles.pagination}
dotContainerStyle={styles.dotContainer}
inactiveDotStyle={styles.inactiveDotStyle}
/>
</View>
Is there something I am missing. Also, is there an alternative library that runs better with large data ?
Try this alternative library: react-native-banner-carousel-updated
I'm using this with more than 20 images and it's works fine.
I'm assuming that the optimization you've tried is what is described in the react-native-snap-carousel library docs...
I too found that every swipe was causing my screen's component to re-render.
You might be thinking...
I think it has to do with the state I am updating each time I scroll the component is re-rendered. Do you have ant idea how to solve this ?
To prevent the re-rendering of your <Carousel ... /> component, the optimization that you want to look at is to utilize React.memo()
Try refactoring your <Carousel ... /> component to a new component file, something like this...
Gallery.js
import React from "react";
import CarouselCardItem, { SLIDER_WIDTH } from "./CarouselCardItem";
import { ALL_RECIPES } from "../config/Recipe/allRecipes";
import Carousel from "react-native-snap-carousel";
const Gallery = ({ carouselRef, selectedItems, setActiveSlide}) => {
console.log("render"); // <== This will render only when props change (ie. the ref - which should not change, or you pass fresh data - in which case you want it to re-render)
return (
<Carousel
initialNumToRender={selectedItems.length}
maxToRenderPerBatch={5}
ref={carouselRef}
swipeThreshold={5}
itemWidth={wp(375)}
data={selectedItems} // <== selectedItems could be passed in as prop, or from app state
sliderWidth={wp(375)}
enableMomentum={false}
lockScrollWhileSnapping
renderItem={renderItem}
onSnapToItem={(index) => setActiveSlide(index)}
/>
);
};
const GalleryMemo = React.memo(Gallery);
export default GalleryMemo;
Then in your screen file, use it
<GalleryMemo carouselRef={carouselRef} selectedItems={selectedItems} setActiveSlide={setActiveSlide}/>
I have a need to dynamically set the OnPressIn prop of a TextInput. I have a ref to the TextInput, but can't figure out how to set this method.
const inputRef = useRef(null);
<TextInput
...
ref={inputRef)
/>
// inputRef is passed as a prop to another component, then I try to set OnPressIn. Neither of these techniques work:
inputRef.setNativeProps({
OnPressIn: () => console.log('ONPRESS TRIGGERED'),
});
inputRef.OnPressIn = () => console.log('ONPRESS TRIGGERED');
How can I set this prop on a TextInput ref?
I believe you're missing "current".
inputRef.current.setNativeProps({
OnPressIn: () => console.log('ONPRESS TRIGGERED'),
});
Also, on what occasion does your onPressIn need to be changed? Isn't using a condition easier?
const handleOnPressIn = () => {
if (condition) {
console.log(`ONPRESS TRIGGERED condition: ${condition}`)
} else {
console.log(`ONPRESS TRIGGERED condition: ${condition}`)
}
}
<TextInput
onPressIn={() => handleOnPressIn()}
/>
If you're aiming for performance optimisation, I believe you should also consider wrapping the setNativeProps call in a useCallback() hook, as from the React Native docs on setNativeProps to edit TextInput value.
In the following code, I expect OfferList to rerender when I add an offer item to the store. OfferList itself is not an observable, but the offer array is passed as a prop.
export const MerchantScreen: FC = observer(() => {
const { merchantStore } = useStores()
return (
<View>
<OfferList data={merchantStore.offers} />
<View>
<Button title={"New Offer"} onPress={() => merchantStore.addOffer()}/>
</View>
</View>
)
})
export const OfferList: FC<OfferListProps> = ({ data }: OfferListProps) => {
const renderItem = (offer: ListRenderItemInfo<any>) => {
return (
<Text>{offer.name}</Text>
)
}
return (
<FlatList
data={data}
renderItem={renderItem}
keyExtractor={(item) => item.id}
/>
)
}
I use Mobx State Tree. All merchantStore.addOffer() does for now is push another offer item into the array.
What I tried / findings:
When I read from the store in my MerchantScreen, e.g. by adding
<Text>{ merchantStore.offers.toString() }</Text>
, the OfferList will also update. I suspect that reading from the store directly in the parent component will force a rerender of the child component as well.
I stumbled upon some answers here that would indicate that a missing key attribute within the FlatList renderItems could be the issue. Tried using key={item.id} to no avail. Also, as you can see I use the keyExtractor prop of FlatList.
Another answers suggested introducing local state to the component like this:
export const OfferList: FC<OfferListProps> = ({ data }: OfferListProps) => {
const [offers, setOfferss] = useState()
useEffect(() => {
setOffers(data)
}, [data])
const renderItem = (offer: ListRenderItemInfo<any>) => {
return (
<Text>{offer.name}</Text>
)
}
return (
<FlatList
data={offers}
renderItem={renderItem}
keyExtractor={(item) => item.id}
/>
)
}
This does not work and my gutfeeling is that this is not how it's done.
As you see my MerchantScreen parent component is an observable while my child component OfferList is not. From my expectation, the observer on my parent component should be enough. The parent component should already detect the change in the store and rerender. The child component in itself does not even use stores.
Overall, the problem at hand seems quite trivial so I guess I am just missing out on an important detail.
MobX only tracks data accessed for observer components if they are directly accessed by render, so if you want to react to each of the offers you need to access them somewhere. You sort of did when you tried merchantStore.offers.toString(), that's why it worked.
So first of all you need to make OfferList an observer.
But then you have FlatList which is native component and you can't make it an observer. What you can do is to access each offers item inside OfferList (just to subscribe for updates basically) like that data={offers.slice()} or even better with MobX helper method toJS data={toJS(offers)}
Depending on your use case you might also want to use <Observer> inside renderItem callback:
const renderItem = (offer: ListRenderItemInfo<any>) => {
return (
<Observer>{() => <Text>{offer.name}</Text>}</Observer>
)
}
When I use onEndReached function in FlatList, it gets called automatically.
Below is the link of this issue.
Link
Is there a solution available for it or any alternative in iOS?
Edited:
Below is the code I tried but this doesn't seems to work.
constructor(props){
super(props);
this.state = {
flatListReady:false
}
}
loadMore(){
if(!this.state.flatListReady){
return null;
}
else{
alert("End Reached")
}
}
_scrolled(){
this.setState({flatListReady:true});
}
render() {
return (
<Layout style={{ flex: 1 }}>
<FlatList
data={listData}
renderItem={({item}) => this._renderItem(item)}
keyExtractor={(item, index) => item.key}
onEndReached={() => this.loadMore()}
onEndReachedThreshold={0.5}
onScroll={() => this._scrolled()}
/>
</Layout>
Try this,
onEndReachedThreshold={0.5}
onEndReached={({ distanceFromEnd }) => {
if(distanceFromEnd >= 0) {
//Call pagination function
}
}}
Sometimes things don't work like they are supposed to, at the end of the day it's not native code where, so may the order of your components or the fact that the Flatlist is encapsulated in a component that is not intended to be, or there is some property should be passed to the Flatlist component itself to activate the onEndReached callback properly.
I've faced this myself, and I didn't know what to do to make it work properly.
A beautiful workaround is derived from the fact the Flatlist inherits ScorllView properties. so you could use the onScroll property to detect if the end has reached or not.
<FlatList
data={this.props.dashboard.toPreviewComplaints}
onScroll={({nativeEvent})=>{
//console.log(nativeEvent);
if(!this.scrollToEndNotified && this.isCloseToBottom(nativeEvent)){
this.scrollToEndNotified = true;
this.loadMoreData();
}
}}
/>
this.scrollToEndNotified is used as a flag not to abuse the call to the loadMore endpoint
isCloseToBottom({layoutMeasurement, contentOffset, contentSize}){
return layoutMeasurement.height + contentOffset.y >= contentSize.height - 100;
}
So whenever it succeed in the isCloseToBottom call it means that you have reached the end of the list, so you can call the loadMoreData function
handle this function very carefully,
endReached=()=>{
//take care of ES6 Fat arrow function and trigger your conditions properly with current state and new state data or current state with new Props.
Based on those conditions only, you need to trigger the other API call
}
<FlatList data={this.state.data}
extraData={this.state.load}
renderItem={this.renderCard}
keyExtractor={item => item.fundRequestId}
onEndReached={this.endReached}
onEndReachedThreshold={.7}
ListFooterComponent={this.renderFooter}
/>
I am trying to toggle ios Switch in react native. But the switch comes back to initial position as soon as I change it.
What I have:
class ABC extends Component {
constructor(props) {
super(props)
this.state = {
obj: []
}
}
fetch(){
// fetch something from remote server, set it to state object array
}
setStatus(id, value){
var temp = [...this.state.obj]
temp.map((t) => {
if (t.id == id) {
t.flag = value
}
})
this.setState({ obj: temp })
}
render() {
return (
<View>
<FlatList
data={this.state.obj}
renderItem={({ item }) =>
<View>
<Text>{item.name}</Text>
<Switch
onValueChange={(val) => this.setStatus(item.id, val)}
value={item.flag}
/>
</View>
}
keyExtractor={({ id }, index) => id.toString()}
/>
</View>
);
}
}
I logged the before and after value of obj state and they seem to update. Should the FlatList be rendered again (like a web page refresh) ? Or is there something I am missing ? Searched SO for answers, couldn't find my mistake.
Flatlist has a prop called extraData.
This prop tells Flatlist whether to re-render or not.
If data in extraData changes then flatlist re-renders based on new data provided in data prop.
So whenever you need to re-render flatlist just change something in extraData.
Best way is to pass state toextraData which is passed to Data.
So, just pass extraData={this.state.obj}.
there also other way called forceUpdate.
you can call this.forceUpdate().
but this is not recommended because this will render not only flatlist but entire component in which you are calling this.