FlatList calls `onEndReached` when it's rendered - react-native

Question

Here is render() function for my simple category list page.
Recently I added pagination for my FlatList View so when the user scrolls to the bottom, onEndReached is called in a certain point(onEndReachedThreshold value length from the bottom), and it will fetch the next categories and concatenate the categories props.
But my problem is onEndReached is called when render() is called In other words, FlatList's onEndReached is triggered before it reach the bottom.
Am I putting wrong value for onEndReachedThreshold? Do you see any problem?
return (
<View style={{ flex:1 }}>
<FlatList
data={this.props.categories}
renderItem={this._renderItem}
keyExtractor={this._keyExtractor}
numColumns={2}
style={{flex: 1, flexDirection: 'row'}}
contentContainerStyle={{justifyContent: 'center'}}
refreshControl={
<RefreshControl
refreshing = {this.state.refreshing}
onRefresh = {()=>this._onRefresh()}
/>
}
// curent value for debug is 0.5
onEndReachedThreshold={0.5} // Tried 0, 0.01, 0.1, 0.7, 50, 100, 700
onEndReached = {({distanceFromEnd})=>{ // problem
console.log(distanceFromEnd) // 607, 878
console.log('reached'); // once, and if I scroll about 14% of the screen,
//it prints reached AGAIN.
this._onEndReachedThreshold()
}}
/>
</View>
)
UPDATE I fetch this.props.categories data here
componentWillMount() {
if(this.props.token) {
this.props.loadCategoryAll(this.props.token);
}
}

Answer 1

Try to implement onMomentumScrollBegin on FlatList :
constructor(props) {
super(props);
this.onEndReachedCalledDuringMomentum = true;
}
...
<FlatList
...
onEndReached={this.onEndReached.bind(this)}
onEndReachedThreshold={0.5}
onMomentumScrollBegin={() => { this.onEndReachedCalledDuringMomentum = false; }}
/>
and modify your onEndReached
onEndReached = ({ distanceFromEnd }) => {
if(!this.onEndReachedCalledDuringMomentum){
this.fetchData();
this.onEndReachedCalledDuringMomentum = true;
}
}

Answer 2

I've got it working with
<Flatlist
...
onEndReached={({ distanceFromEnd }) => {
if (distanceFromEnd < 0) return;
...
}
...
/>

Answer 3

First check if the FlatList is inside a ScrollView or Content of native-base. Then take it outside of it
Actually you don't need to use Content or ScrollView, as FlatList has both ListFooterComponent and ListHeaderComponent.
Though it is not recommended, if you really need to use Flatlist inside ScrollView, then take a look at this answer: https://stackoverflow.com/a/57603742/6170191

Answer 4

After hours of trying different approaches I got it to work by wrapping the Flatlist with a View of fixed height and flex:1.
With this settings, I was able to get onEndReached called once and only after I scroll near the bottom. Here's my code sample:
render() {
const {height} = Dimensions.get('window');
return (
<View style={{flex:1, height:height}}>
<FlatList
data={this.props.trips_uniques}
refreshing={this.props.tripsLoading}
onRefresh={()=> this.props.getTripsWatcher()}
onEndReached={()=>this.props.getMoreTripsWatcher()}
onEndReachedThreshold={0.5}
renderItem={({item}) => (
<View style={Style.card}>
...
...
</View>
)}
keyExtractor={item => item.trip_id}
/>
</View>
)
}
My onEndReached() function just calls the API and updates my data. It doesn't do any calculations with regards to distance to bottom or threshold

Answer 5

Most of the times, this error is caused because of an incorrect use of onEndReachedThreashold, which also depends of the number of items you are rendering (more items, more scroll size).
Try to follow this logic:
If 10 items cover your screen, and you are rendering 20 items on each scroll, then set onEndReachedThreashold to 0.8.
If 2 or 3 items cover your screen, and you are rendering 10 items on each scroll, then set onEndReachedThreashold to 0.5.
Also, use initialNumToRender = numItems. For some reason, using this FlatList prop helps to reduce the chance of multiple onEndReached calls.
Just play with onEndReachedThreashold value.
Other times, this error is produced because of nesting scroll views. Do not put your FlatList inside of a ScrollView. Instead, take use of the FlatList header and footer props.
For both solutions, I suggest to set the FlatList style and contentContainerStyle to { flexGrow: 1 }.

Answer 6

Remove every Scrollable View inside your FlatList

Answer 7

If you want to show 3 or 4 records and want to load the next data just when you reach the end. Set onEndReachedThreshold to 0 or 0.1.

Answer 8

Maybe You can bypass this FlatList bug by incrementing your page before doing async call, and then you will fetch data on every onEndReached fiers and not get errors about duplicate keys

Answer 9

(as of NOV19)
Keep flatlist as the only component inside of a single view
Set style of that single view from dimensions like
{{flex: 1, height: Dimensions.get('window').height}}

Answer 10

If FlatList is on another FlatList or ScrollView the onEndReached call immediately when rendered component to resolve that problem doesn't wrap FlatList with another.

Answer 11

A bit late but I just ran into this issue and I fixed it by passing to my <FlatList/> the initialNumToRender prop. This prop is 10 by default so if you don't set it and your screen shows more than 10 items on the initial render, it is going to trigger onEndReached since it has passed the 10th element.
initialNumToRender should probably be the same as the amount of elements you fetch per page.

Answer 12

I have a <FlatList> (from react-native) inside an <Overlay> (from react-native-elements.) I have the problem of onEndReached being executed as soon as the component is rendered for the 1st time and before the user does anything.
The problem was resolved by using <Modal> (from react-native), instead of <Overlay>.

Answer 13

If you are using hooks, here you can find the hook version of #Ilario answer:
const onEndReachedCalledDuringMomentum = useRef(true)
onEndReachedHandler = ({ distanceFromEnd }) => {
if(!onEndReachedCalledDuringMomentum.current){
fetchData()
onEndReachedCalledDuringMomentum.current = true
}
}
<FlatList
...
onEndReached={onEndReachedHandler}
onEndReachedThreshold={0.7}
onMomentumScrollBegin={() => { onEndReachedCalledDuringMomentum.current = false }}
/>

Answer 14

This simple solution worked for me. Note the "refreshing" state is controlled by an async API call in a useEffect hook to retrieve data for the FlatList.
const onEndReachedHandler = () => {
if (!refreshing) ...
}
<FlatList
...
data={mydata}
onEndReached={onEndReachedHandler}
onEndReachedThreshold={0.7}
refreshing={refreshing}
/>

Answer 15

I struggled around the whole day but the issue that I was getting is, I am using FlatList inside ScrollView. So, Remove Scrollview & then use Flatlist independently. This will solve my problem.

Answer 16

From my experience, you can simply utilize onEndReachedThreshold props in your FlatList or SectionList and pass a very very small number like 0.001 to it.
onEndReachedThreshold={0.001}
According to docs for FlatList, onEndReachedThreshold is units of length from the bottom in list items.
How far from the end (in units of visible length of the list) the
bottom edge of the list must be from the end of the content to trigger
the onEndReached callback. For example, a value of 0.5 will trigger
onEndReached when the end of the content is within half the visible
length of the list.
Thus, a very small value like 0.001 helps you to make sure that onEndReached is only gonna be called when the end of the content is within the very end of the visible length of the list.
Hope this helps :) Sorry for bad English.

Answer 17

The solution is simpler than anyone would think.
Just add an !isLoading condition for fetch calling. It works for me:
onEndReached={() => {
if (!isLoading) {
fetchProducts();
}
}}
And the full code with ScrollView and FlatList:
<ScrollView
horizontal={true}
showsVerticalScrollIndicator={false}
showsHorizontalScrollIndicator={false}
style={styles.mainContainer}>
<FlatList
ListHeaderComponent={TableHeader}
data={displayedProducts}
renderItem={(item: ListRenderItemInfo<IProduct>) => TableRow(item, showDeleteModal)}
keyExtractor={keyExtractor}
ListFooterComponent={<Loading loadingText={'Loading products...'} />}
onEndReached={() => {
if (!isLoading) {
fetchProducts();
}
}}
onEndReachedThreshold={0.8}
stickyHeaderIndices={[0]}
/>
</ScrollView>

Answer 18

I have solved it with using debounce from lodash. Firstly, I import debounce from 'lodash.debounce'. Then I use debounce for load more function with 500 ms interval
<Flatlist
onEndReached = {debounce(this._onLoadMore, 500)}
/>