Flatlist Image source in React Native - react-native

I am trying to render a FlatList in React Native that it will be like an image carousel.
I want to provide the image sources in the assets folder and pass each items source in the renderItem but i get error undefined is not an object.
Here is the state:
export default function App() {
const [images, setimages] = useState([
{src:require('./assets/image1.png'),key:'1'},
{src:require('./assets/image2.png'),key:'2'},
{src:require('./assets/image3.png'),key:'3'},
{src:require('./assets/image4.png'),key:'4'},
{src:require('./assets/image5.png'),key:'5'}
]);
And here is the FlatList:
<FlatList
horizontal={true}
showsHorizontalScrollIndicator={false}
data={images}
renderItem={ ({images}) => (
<Image source={images.src} style={{
width:260,
height:300,
borderWidth:2,
borderColor:'#d35647',
resizeMode:'contain',
margin:8
}}></Image>
)}
/>

React Native FlatList renderItem callback get an object parameter with 3 props, item, index and separators:
renderItem
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
}}
/>
)}
/>
);
UPDATE
We should never use indexes for JSX keys because on a rearrangement or the array, we'll end up with the same indexes pointing to different items.
There is an ESLint rule regarding that issue eslint-plugin-react:
eslint-plugin-react
Prevent usage of Array index in keys (react/no-array-index-key)
Warn if an element uses an Array index in its key.
The key is used by React to identify which items have changed, are added, or are removed and should be stable.
It's a bad idea to use the array index since it doesn't uniquely identify your elements. In cases where the array is sorted or an element is added to the beginning of the array, the index will be changed even though the element representing that index may be the same. This results in unnecessary renders.
We should create unique keys for each item (and maybe store them inside our images array if we have a large items count) by using some fast hashing algorithms like CRC32 on the image name or by using nanoid to generate a random key for each image.

This is happening because you're trying to destructure a images parameter which doesn't exist, it's called item.
Try this instead:
return (
<FlatList
horizontal
showsHorizontalScrollIndicator={false}
data={images}
renderItem={({ item }) => (
<Image
source={item.src}
style={{
width:260,
height:300,
borderWidth:2,
borderColor:'#d35647',
resizeMode:'contain',
margin:8
}}
/>
)}
/>
);

the comment above is correct, however there is the uri attribute inside the source where you assign the url of the image see:
return (
<FlatList
horizontal
showsHorizontalScrollIndicator={false}
data={images}
renderItem={({ item }) => (
<Image
source={{ uri: item.src }}
style={{
width:260,
height:300,
borderWidth:2,
borderColor:'#d35647',
resizeMode:'contain',
margin:8
}}
/>
)}
/>
);

Related

Use Images from Array in flatlist

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
}}
/>
)}
/>
);

React Native FlatList performance improvements

I'm reading barcodes and every barcode I read I add to an array and show in flatlist. but after 30 barcodes adding to the array getting slow. is there any solution I can do?
renderItem:
const renderItem = useCallback(
({item, index}) => (
<View style={styles.ListItemContainer}>
<Text>
-{item} index: {index}
</Text>
<TouchableOpacity
onPress={() => {
setRemovedItem(index);
setShowAlert(true);
}}>
<Text style={{fontSize: 20, fontWeight: 'bold'}}>X</Text>
</TouchableOpacity>
</View>
),
[],
);
FlatList component:
<FlatList
renderItem={renderItem}
data={barcodeArray}
style={styles.ListContainer}
keyboardShouldPersistTaps="handled"
initialNumToRender={12}
removeClippedSubviews
windowSize={12}
maxToRenderPerBatch={12}
/>
adding barcode:
const readBarcode = barcode => {
setbarcodeArray([barcode, ...barcodeArray]);
setbarcodeValue('');
setkey(key + 1);
};
for this solution you can use VirtualizedList instead Flatlist . In general, this should only really be used if you need more flexibility than FlatList .
for more info see this
Did you try using this: https://github.com/Flipkart/recyclerlistview library. It renders far fewer items than FlatList and then recycles them. Should be must faster and more performant than the native flatlist. If this does not work then try to use getItemLayout in flatlist if you have a fixed height of the content.

ERROR - VirtualizedLists should never be nested inside plain ScrollViews with the same orientation

I'm working on a react-native app and I have to put a list of object in a Scrollview, so I use the FlatList component to do it. This is the piece of code that generates the error:
<ScrollView contentContainerStyle={style}>
Other components
<FlatList
style={style}
data={data}
scrollEnabled={false}
keyExtractor={(item, index) => index.toString()}
renderItem={({ item, index}) => (somethings)}
/>
Other components
</ScrollView>
The complete error is: VirtualizedLists should never be nested inside plain ScrollViews with the same orientation because it can break windowing and other functionality - use another VirtualizedList-backed container instead.
Avoid using FlatList with the same orientation. Instead, restructure your code like this --
<ScrollView contentContainerStyle={style}>
Other components
{
data.map((item)=> <Somthing item={item}/>)
}
Other components
</ScrollView>
Flatlist has its own ScrollView you can scroll through the list using that so there is no need to put a flatlist into a ScrollView that is why its giving a warning, the both scrollview will clash and one of them (mostly the parent one) works.
The error is self explanatory and it should be in a developers best interest to avoid these kind of things even when it's just a false alarm.
Your particular situation could use the following solution:
<FlatList
data={data}
keyExtractor={(item, index) => `key-${index}`}
ListHeaderComponent={() => (
<SomeComponents>
...Some components those need to be on top of the list
</SomeComponents>
)}
ListFooterComponent={() => (
<SomeComponents>
...Some components those need to be below the list
</SomeComponents>
)}
renderItem={({ item, index}) => (somethings)}
/>
Another note, if you need more complex list that needs header and footer for the list itself, you can try SectionList.
Your component FlatList and ScrollView have the same orientation(vertical), so you need put your component inside a ScrollView with horizontal orientation like this:
<View>
<ScrollView nestedScrollEnabled={true} style={{ width: "100%" }} >
<View>
<ScrollView horizontal={true} style={{ width: "100%" }}>
<FlatList />
</ScrollView>
</View>
</ScrollView>
</View>
Solution 1: Use FlatList props ListHeaderComponent and create all of your page top section in that. Something like this:
This will not show any warning or error.
Solution 2:
Because only parent view will scroll (ScrollView) and not the child FlatList, so to get rid of the warning you can pass a prop scrollEnabled={false} to the FlatList.
If it doesn't go then import LogBox from react-native and write this in your component
useEffect(() => {
LogBox.ignoreLogs(["VirtualizedLists should never be nested"])
}, [])
hopefully, the warning will be removed.
Anyone want to solve this issue can use a custom VirtualizedScrollView like this:
import React from 'react';
import { FlatList } from 'react-native';
const VirtualizedScrollView = props => {
return (
<FlatList
{...props}
data={[]}
keyExtractor={(e, i) => 'dom' + i.toString()}
ListEmptyComponent={null}
renderItem={null}
ListHeaderComponent={() => (
<>{props.children}</>
)}
/>
);
};
export default VirtualizedScrollView;
Then if you use FlatList inside VirtualizedScrollView, it won't get the warning/error.
<VirtualizedScrollView>
<FlatList
/*--- your props ---*/
/>
</VirtualizedScrollView>
There is a npm package where I get this code, you can also use this package
Solution:
I have also encountered same problem with FlatList. Then the package below solved my problem.
'react-native-virtualized-view'
import { ScrollView } from 'react-native-virtualized-view'
if ScrollView is Vertical change Flatlist Horizontal
<ScrollView >
<FlatList
horizontal
data={lenders}
keyExtractor={(_, index) => index}
renderItem={(item) => {
return <Text>item</Text>
}}
/>
You can solve the 2 vertical ones(I'm assuming their side by side, separated with a segemented control?) by using the same flat list and switching out the data when it's switched. If they're just two vertical flat list's one after another use the SectionList.
For the horizontal one you can try putting the Horizontal FlatList in the ListHeaderComponent of the vertical FlatList and see what happens. It can be janky if you use a vertical FlatList in a vertical scroll view but maybe with two different axis it might be ok. The other option is two only show a few items in the horizontal scrollview and have a "Show More".
The last option is too re design/rethink the page so it's not doing so much. On mobile less is more and developers/designers like to get in the mindset of porting desktop thinking onto mobile. Might be worth a shot.
I used the SectionList approach to solve this & wanted to post a code example because I found the Section data required by React Native to be clear but also quite prescriptive.
renderList = ({empty, posts}: {empty: boolean, posts: Array<Object>}) => (
<SectionList
sections={[
{type: 'MAP', data: [{}]}, // Static sections.
{type: 'PROFILE', data: [{}]},
{type: 'POSTS', data: posts} // Dynamic section data replaces the FlatList.
]}
keyExtractor={(item, index) => index}
renderItem={({item, section}) => {
switch (section.type) {
// Different components for each section type.
case 'MAP':
return <MapView />;
case 'PROFILE':
return <Profile />;
case 'POSTS':
return <Post item={item} />;
default:
return null;
}
}}
ItemSeparatorComponent={() => <Separator />}
ListFooterComponent={() => <>{empty && <EmptyList />}</>}
/>
);
What's nice is that the content feels logically quite separate, so you can add sections easily or have different dynamic data sources.
(If you're building a form & want better keyboard handling, you could also try a KeyboardAwareSectionList from react-native-keyboard-aware-scroll-view.)
Flatlist has an integrated scrollview itself, so you can resolve this error by removing ScrollView Component, And let just the Fatlist component
Error ? you are trying to render a FlatList component inside a scrollview component, this is what is throwing the warning.
solution Render the components using Flatlist's ListHeaderComponent={} prop, i.e in your flatlist add the prop as follows
const FlatList_Header = () => {
return (
<View style={{
height: 45,
width: "100%",
backgroundColor: "#00B8D4",
justifyContent: 'center',
alignItems: 'center'
}}
>
<Text style={{ fontSize: 24, color: 'white' }}> Sample FlatList Header </Text>
</View>
);
}
<FlatList
data={BirdsName}
renderItem={({ item }) => <ItemRender name={item.name} />}
keyExtractor={item => item.id}
ItemSeparatorComponent={ItemDivider}
**ListHeaderComponent={FlatList_Header}**
ListHeaderComponentStyle={{ borderBottomColor: 'red', borderBottomWidth: 2 }}
/>
Note the use of the ListHeaderComponent in the code above, that should supress the warning.
Use flatList like this ListHeaderComponent and ListFooterComponent:
<FlatList ListHeaderComponent={
<ScrollView
style={styles.yourstyle}
showsVerticalScrollIndicator={false}
>
<View style={styles.yourstyle}>
</View>
</ScrollView>
}
data={this.state.images}
renderItem={({ item, index }) => {
return (
<View
style={styles.yourstyle}
>
<Image
source={{
uri: item,
}}
style={styles.yourstyle}
resizeMode={"contain"}
/>
<Text
numberOfLines={2}
ellipsizeMode="tail"
style={styles.yourstyle}
>
{item.name}
</Text>
</View>
);
}}
keyExtractor={({ name }, index) => index.toString()}
ListFooterComponent={
<View style={styles.yourstyle}></View>
}
/>
In my case it was happening due to nesting of ScrollView.
Try replacing some of the ScrollView from children components with React.Fragment.
The solution is very simple, please do not put the Flatlist component in the ScrollView.
They both have the same functionality but Flatlist has advantages and is more stable to use.

How to prevent flatlist header or footer from re-render in reactnative

I put an input field in the footer of flatlist but when i try to type anything it dismiss the keyboard automatically because of the re-render of the flatlist footer..
I tried to nest the flatlist from Scrollview but this brings warning..
How can i stop the footer from being re-rendered? can i fix this without nest the flatlist from Scrollview?
<FlatList
ListHeaderComponent={() => (
<View style={styles.discountContainer}>
<Text style={[styles.buttonText, { letterSpacing: 3 }]}>
10% DISCOUNT ON 8 COURSES
</Text>
</View>
)}
numColumns={2}
data={data}
renderItem={({ item }) => (
<View>
<SingleProduct item={item} />
</View>
)}
ListFooterComponent={() => (
<View>
<View style={styles.couponContainer}>
<Input
placeholder='Coupon code'
placeholderTextColor='#0a5796'
color='#0a5796'
inputStyle={{
color: '#0a5796',
}}
inputContainerStyle={{
borderBottomWidth: 0,
height: 50,
}}
containerStyle={styles.couponInputContainer}
onChangeText={(value) =>
this.setState({ couponCode: value })
}
value={this.state.couponCode}
/>
{couponLoading ? (
<View style={styles.couponButton}>
<ActivityIndicator />
</View>
) : (
<TouchableOpacity
style={styles.couponButton}
onPress={() => this.codeCheck(couponCode, line_items)}
>
<Text style={styles.buttonText}>Apply Coupon</Text>
</TouchableOpacity>
)}
</View>
</View>
)}
/>
Arrow-Funktions are "always" executed and create a new Reference in Memory. This way they will always re-rendering if component will be executed.
For performance reasons you better define your function outside and call it like this:
function renderMyItem(){ ...bimbom... yous stuff goes here! }
function renderHeader(){ ...bimbom... yous stuff goes here! }
<Flatlist
renderItem={this.renderMyItem()}
ListHeaderComponent={this.renderHeader()}
...
/>
What happens here?
Both of your functions renderMyItem and renderHeader will be executed once if your component is loaded and will be saved in memory. So every time you call one of the functions, you call a reference to the place in memory where they are saved.
In the other case, Arrow-Functions ()=>{...} are executed in current context and generate a new reference in Memory, each time they called, because .. to say it clear: you define & call a function that way.
If you are using Functional Component then don't use Arrow function () => (...) for header and footer components of FlatList but instead only return your header and footer Components as shown in the sample below.
<FlatList
...
ListHeaderComponent={(<View><Text>Header</Text></View>)}
ListFooterComponent={(<View><Text>Footer<Text></View>)}
/>
I was going through the same problem and the accepted answer didn't worked for me. As here the problem occurs because we are updating the state whenever the text changes (as defined in onChangeText) which causes re-rendering. Thus i came up with another solution;
First i created another dict object newState which has nothing to do with state or props. So on changing newState dict, it will not cause re-rendering. Then;
newState = {}
<TextInput onChangeText={text => this.newState.value = text} />
Then i changed the state(which is necessary as per your problem and as per mine) on onEndEditing ;
<TextInput onChangeText={text => this.newState.value = text} onEndEditing={this.setSearch} />
Here is setSearch
setSearch= () => {
this.setState({couponCode: this.newState.value})
delete this.newState.value;
}
I am deleting the key after the state is set because it doesnot update correctly next time.

Make VirtualizedList show as Grid

I'm trying to make something like this:
The problem: The project was built with immutablejs and according to React Native Docs, I can't use FlatList thus I can't use numColumns props feature of that component.
AFAIK, my only choice is to use VirtualizedList as the docs points out, but I can't figure out how to display the cells as a grid as shown above.
I've already tried to add style props in both cell and view wrapper, but none of the code used to align the cells, like the picture I posted, is ignored. In fact it was showing perfect when I was using ScrollView, but due the HUGE lag I'm moving the code to VirtualizedList.
Any help? Anything would be welcome, I already digged a lot on Google but I can't find anything about this.
Some sample code:
<View>
<VirtualizedList
data={props.schedules}
getItem={(data, index) => data.get(index)}
getItemCount={(data) => data.size}
keyExtractor={(item, index) => index.toString()}
CellRendererComponent={({children, item}) => {
return (
<View style={{any flexbox code gets ignored here}}>
{children}
</View>
)}}
renderItem={({ item, index }) => (
<Text style={{also here}} key={index}>{item.get('schedule')}</Text>
)}
/>
</View>
Answering my own question:
I got it working by copying the FlatList.js source code from react-native repo.
Here's an example code:
<VirtualizedList
data={props.schedules}
getItem={(data, index) => {
let items = []
for (let i = 0; i < 4; i++) {
const item = data.get(index * 4 + i)
item && items.push(item)
}
return items
}}
getItemCount={(data) => data.size}
keyExtractor={(item, index) => index.toString()}
renderItem={({item, index}) => {
return (
<View key={index} style={{flexDirection: 'row'}}>
{item.map((elem, i) => (
<View key={i}>
<Text key={i}>{elem.get('horario')}</Text>
</View>
))}
</View>
)
}}
/>
The number 4 is for the number of columns. The key parts are in the getItem and adding flexDirection: 'row' at renderItem in the View component.