I am implementing one scenario in which I am getting data from backend but I need to show image with each item. The image will come from local asset folder. I tried to use both array with flat-list but there is issue with the same. Could anyone let me know how to resolve that.
I am not able to understand how to implement that logic.
Thanks in advance!
React Native FlatList renderItem callback get an object parameter with 3 props, item, index and separators:
renderItem({item, index, separators});
You don't have to define keys in your array, just the images sources and then use item and index inside your renderItem function:
Define just an array with the sources:
const [images, setimages] = useState([
require('./assets/image1.png'),
require('./assets/image2.png'),
require('./assets/image3.png'),
require('./assets/image4.png'),
require('./assets/image5.png')
]);
And use item and index for source and key:
return (
<FlatList
horizontal={true}
showsHorizontalScrollIndicator={false}
data={images}
renderItem={ ({ item, index }) => (
<Image source={item} /* Use item to set the image source */
key={index} /* Important to set a key for list items,
but it's wrong to use indexes as keys, see below */
style={{
width:260,
height:300,
borderWidth:2,
borderColor:'#d35647',
resizeMode:'contain',
margin:8
}}
/>
)}
/>
);
How we can implement onStartReached in FlatList ?
I used horizontal list.
I have some idea of using onScroll using,but I thing this not properly.
Seems onRefresh could do the job.
https://reactnative.dev/docs/flatlist#onrefresh
it must be start reached and pull to trigger onRefresh.
If you need a infinite scroll i used this
<FlatList
data={data}
renderItem={({ item, index }) => {
return (
// Component to render
);
}}
keyExtractor={(item) => item.uid}
onEndReached={() => //Load more data}
onEndReachedThreshold={0.5} // "Sleep" time
initialNumToRender={10} // initial number to items
/>
otherwise the way to use onStartReached is identical to onEndReached
I work on a horizontal list with the component FlatList in the tvOS environment. The problem occurs on a small list of 3 elements, I set the initialScrollIndex equal to the second or last element, the good item is selected. However when I try to go back on a previous item the selection occurs but there is no scroll.
<FlatList
getItemLayout={(data, index) => ({
length: 300,
offset: 300 * index,
index,
})}
initialScrollIndex={this.props.initialScrollIndex}
keyExtractor={this._keyExtractor}
horizontal={this.props.horizontal}
scrollEnabled={true}
extraData={this.state}
ref={list => (this.myScrollView = list)}
data={this.finalData}
removeClippedSubviews={false}
renderItem={this.props.renderRow}
/>
Have you tried changing the properties of the returning object within getItemLayout from length: 300 to width: 300. I would think this should be width rather than length because you are rendering a horizontal FlatList.
getItemLayout={(data, index) => ({
width: 300, //- Here
offset: 300 * index,
index,
}
)}
I am trying to create a chat in React native using a <Flatlist />
Like WhatsApp and other chat apps, the messages start at the bottom.
After fetching the messages from my API, I call
this.myFlatList.scrollToEnd({animated: false});
But it scrolls somewhere in the middle and sometimes with fewer items to the bottom and sometimes it does nothing.
How can I scroll initially to the bottom?
My chat messages have different heights, so I can't calculate the height.
I had similar issue. If you want to have you chat messages start at the bottom, you could set "inverted" to true and display your messages and time tag in an opposite direction.
Check here for "inverted" property for FlatList. https://facebook.github.io/react-native/docs/flatlist#inverted
If you want to have you chat messages start at the top, which is what I am trying to achieve. I could not find a solution in FlatList, because as you said, the heights are different, I could not use getItemLayout which make "scrollToEnd" behave in a strange way.
I follow the approach that #My Mai mentioned, using ScrollView instead and do scrollToEnd({animated: false}) in a setTimeout function. Besides, I added a state to hide the content until scrollToEnd is done, so user would not be seeing any scrolling.
I solved this issue with inverted property and reverse function
https://facebook.github.io/react-native/docs/flatlist#inverted
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse
<FlatList
inverted
data={[...data].reverse()}
renderItem={renderItem}
keyExtractor={(item) => item.id}
/>
You can use this solution in chat component.
I faced the same issue with you and then I moved to use ScrollView.
It is fixed:
componentDidMount() {
setTimeout(() => {
this.scrollView.scrollToEnd();
});
}
<ScrollView ref={(ref) => { this.scrollView = ref; }} style={styles.messages}>
{
messages.map((item, i) => (
<Message
key={i}
direction={item.userType === 'banker' ? 'right' : 'left'}
text={item.message}
name={item.name}
time={item.createdAt}
/>
))
}
</ScrollView>`
Set initialScrollIndex to your data set's length - 1.
I.e.
<Flatlist
data={dataSet}
initialScrollIndex={dataSet.length - 1}
/>
There are two types of 'good' solutions as of 2021.
First one is with timeout, references and useEffect. Here's the full example using Functional Components and Typescript:
// Set the height of every item of the list, to improve perfomance and later use in the getItemLayout
const ITEM_HEIGHT = 100;
// Data that will be displayed in the FlatList
const [data, setData] = React.useState<DataType>();
// The variable that will hold the reference of the FlatList
const flatListRef = React.useRef<FlatList>(null);
// The effect that will always run whenever there's a change to the data
React.useLayoutEffect(() => {
const timeout = setTimeout(() => {
if (flatListRef.current && data && data.length > 0) {
flatListRef.current.scrollToEnd({ animated: true });
}
}, 1000);
return () => {
clearTimeout(timeout);
};
}, [data]);
// Your FlatList component that will receive ref, data and other properties as needed, you also have to use getItemLayout
<FlatList
data={data}
ref={flatListRef}
getItemLayout={(data, index) => {
return { length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index };
}}
{ ...otherProperties }
/>
With the example above you can have a fluid and animated scroll to bottom. Recommended for when you receive a new message and has to scroll to the bottom, for example.
Apart from this, the second and easier way is by implementing the initialScrollIndex property that will instantly loads the list at the bottom, like that chat apps you mentioned. It will work fine when opening the chat screen for the first time.
Like this:
// No need to use useEffect, timeout and references...
// Just use getItemLayout and initialScrollIndex.
// Set the height of every item of the list, to improve perfomance and later use in the getItemLayout
const ITEM_HEIGHT = 100;
<FlatList
data={data}
getItemLayout={(data, index) => {
return { length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index };
}}
{ ...otherProperties }
/>
I found a solution that worked for me 100%
Added the ref flatListRef to my flatlist:
<Flatlist
reference={(ref) => this.flatListRef = ref}
data={data}
keyExtractor={keyExtractor}
renderItem={renderItem}
/>
Then whenever you want to automatically scroll to bottom of the list use:
this.flatListRef._listRef._scrollRef.scrollToEnd({ animating: true });
yes you should access the element _listRef then _scrollRef then call the scrollToEnd 🙄
react-native 0.64.1
react 17.0.2
I've struggled on this as well and found the best possible solution for me that renders without a glitch is:
Use inverted={-1} props
Reverse the order of messages objects inside my array with data={MyArrayofMessages.reverse()} in my case data={this.state.messages.reverse()} using reverse() javascript function.
Stupidly easy and renders instantaneously !
Use inverted={1} and reverse your data by using the JS reverse function. It worked for me
<FlatList contentContainerStyle={{ flex: 1, justifyContent: 'flex-end' }} />
I am guessing that RN cannot guess your layout so it cannot know how much it needs to "move". According to the scroll methods in the docs you might need to implement a getItemLayout function, so RN can tell how much it needs to scroll.
https://facebook.github.io/react-native/docs/flatlist.html#scrolltoend
Guys if you want FlatList scroll to bottom at initial render. Just added inverted={-1} to your FlatList. I have struggle with scroll to bottom for couple of hours but it ends up with inverted={-1}. Don't need to think to much about measure the height of FlatList items dynamically using getItemLayout and initialScrollIndex or whats so ever.
I found a solution that worked for me 100%
let scrollRef = React.useRef(null)
and
<FlatList
ref={(it) => (scrollRef.current = it)}
onContentSizeChange={() =>
scrollRef.current?.scrollToEnd({animated: false})
}
data={data}/>
If you want to display the message inverted, set "inverted" to true in the flat list.
<Flatlist
data={messageData}
inverted={true}
horizontal={false}
/>
If you just want to scroll to the last message, you can use initialScrollIndex
<Flatlist
data={messageData}
initialScrollIndex={messageArray.length - 1}
horizontal={false}
/>
I spent couple of hours struggling with showing the first message on top without being able to calculate the item's height as it contains links and messages. But finally i've been able to...
What i've done is that i wrapped the FlatList in a View, set FlatList as inverted, made it to take all available space and then justified content. So now, conversations with few messages starts at top but when there are multiple messages, they will end on bottom. Something like this:
<View style={ConversationStyle.container}>
<FlatList
data={conversations}
initialNumToRender={10}
renderItem={({ item }) => (
<SmsConversationItem
item={item}
onDelete={onDelete}
/>
)}
keyExtractor={(item) => item.id}
getItemCount={getItemCount}
getItem={getItem}
contentContainerStyle={ConversationStyle.virtualizedListContainer}
inverted // This will make items in reversed order but will make all of them start from bottom
/>
</View>
And my style looks like this:
const ConversationStyle = StyleSheet.create({
container: {
flex: 1
},
virtualizedListContainer: {
flexGrow: 1,
justifyContent: 'flex-end'
}
};
How to adjust horizontal FlatList with separators in order to skip separators when pagination is enabled. I want to see separators only when swiping between items. I tried to set it in getItemLayout but it doesn't work properly. I used getItemLayout = (_, index) => ({ length: window.width, offset: (window.width + separatorWidth) * index, index }) Behaviour looks like that
This confused me as well.
There are a few snap related properties inherited/extended from <ScrollView> that are useful here.
Checkout: snapToInterval and snapToOffsets.
If you're using a <FlatList> or <ScrollView> to act as a horizontal full-width carousel, and want to enforce snapping so that a single "page" within the list is always within view (i.e. users can't stop partially between views), these snap props are what you need.
Note: you need to disable pagingEnabled in order for these props to be respected.
Simplified example code:
render() {
const totalItemWidth = window.width + separatorWidth;
return (
<FlatList
{ /* ... other props — data, renderItem, style, etc ... */}
horizontal
showsHorizontalScrollIndicator={false}
snapToInterval={totalItemWidth}
decelerationRate="fast"
bounces={false}
getItemLayout={(data, index) => ({
length: totalItemWidth,
offset: totalItemWidth * index,
index,
})}
ItemSeparatorComponent={SomeSeparatorComponent}
/>
)
}
How it behaves on iOS verse Android:
Android is a bit clunkier and I'm still refining the decelerationRate and overall feel... but it's close, IMO.