Basic FlatList code throws Warning - React Native

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FlatList does not seem to be working. I get this warning.

VirtualizedList: missing keys for items, make sure to specify a key property on each item or provide a custom keyExtractor.

Code:

<FlatList 
  data={[{name: 'a'}, {name: 'b'}]} 
  renderItem={
    (item) => <Text key={Math.random().toString()}>{item.name}</Text>
  } 
  key={Math.random().toString()} />

Simply do this:

<FlatList 
  data={[{name: 'a'}, {name: 'b'}]} 
  renderItem={
    ({item}) => <Text>{item.name}</Text>
  } 
  keyExtractor={(item, index) => index.toString()}
/>

Source: here

Basic FlatList code throws Warning - React Native, Simply do this: <FlatList data={[{name: 'a'}, {name: 'b'}]} renderItem={ (item) => <​Text>{item.name}</Text> } keyExtractor={(item, index) => index.toString()} />. Method to get top index of flatlist in react native. Ask Question Asked 2 years, 3 months ago. Basic FlatList code throws Warning - React Native. 13.

You don't need to use keyExtractor. The React Native docs are a little unclear but the key property should go in each element of the data array rather than in the rendered child component. So rather than

<FlatList
  data={[{id: 'a'}, {id: 'b'}]}
  renderItem={({item}) => <View key={item.id} />}
/>
// React will give you a warning about there being no key prop

which is what you'd expect, you just need to put a key field in each element of the data array:

<FlatList
  data={[{key: 'a'}, {key: 'b'}]}
  renderItem={({item}) => <View />}
/>
// React is happy!

And definitely don't put a random string as the key.

React Native: Can't fix FlatList keys warning - reactjs - html, I get this warning. VirtualizedList: missing keys for items, make sure to specify a key property on each item or provide a custom keyExtractor. Code: <FlatList  React native flatlist last item visibility issue. React Native FlatList with columns, Last item width. 123. Basic FlatList code throws Warning - React Native. 0.

This worked for me:

<FlatList
  data={[{name: 'a'}, {name: 'b'}]} 
  keyExtractor={(item, index) => index.toString()}
/>

FlatList, Relevant code: <FlatList data={this.props.tunes} keyExtractor={(item, index) => item.id} renderItem={({item}) Basic FlatList code throws Warning - React Native. If you use index then make sure to use index.toString() or you'll get a different warning (Failed child context type - type number supplied to CellRenderer expected string). FlatList will work with index by default if you don't have key properties or a keyExtractor defined, but it will still throw a warning.

You can use

 <FlatList   
  data={[]}  
  keyExtractor={(item, index) => index.toString()} 
 />

NOTE : Using index.toString() i.e expected to be string.

SectionList throws Warning that is only for FlatList when using , Description While FlatList is scrolling and/or rendering items the JS thread is to host and review code, manage projects, and build software together. react-​native-bot added Ran Commands Stale labels on Feb 23, 2018 It is still a pain in the ass to make a simple FlatList with 100+ Selectable Image. Used to extract a unique key for a given item at the specified index. Key is used for caching and as the react key to track item re-ordering. The default extractor checks item.key, then falls back to using the index, like React does.

Have an 'id' in your data

const data = [
{
  name: 'a',
  id: 1
},
{
  name: 'b',
  id: 2
}];

<FlatList 
  data={data}
  renderItem={
    (item) => <Text>{item.name}</Text>
  } 
  keyExtractor={item => item.id}
/>

Hope this helps !!!

Build Two Full Projects and One Full Game using React Native , SectionList throws Warning that is only for FlatList when using flexWrap #18079 react-native-bot added the Platform: macOS label on Mar 20, 2018 After reviewing the code for SectionList, FlatList, and VirtualizedList,  Teams. Q&A for Work. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

Awesome React Native components, news, tools, and learning , Instead, you can take the HTML route and have a single code base that works In this book, you'll learn React Native, by building real apps, not just simple, contrived see that Node should run any basic JavaScript that you care to throw at it. FlatList has a relatively long list of available props, and that list is made longer,. React-Native: FlatList onRefresh not called on pull up. Current Behavior: I'm trying to update a list gotten from a server by pulling up on the view. When I do the onRefresh does not fire. I've set the GET request in the callback of the setState function, but that didn't seem to do anything.

FlatList using keyExtractor, still getting warning : reactnative, A simple alert to notify users about new chat messages, something went A simple react-native implementation of step indicator widget compatible with the Animated Pagination For React Native's ListView, FlatList, and SectionList A react-native confirmation code field compatible with IOS, Android and Web Platforms. Since v0.43 of React Native we’ve had access to two new list views, the FlatList and the SectionList. Today we will take a look at how to use the FlatList component. What is it?

I am creating a flatList but still getting the warning that I don't have keys on my cli tool to create react native repetative code such as 1.component ( simple and  2. Create constructor() in your class and inside the constructor() we would make a State named as FlatListItems and enter some data in this state array. This would be our FlatList data, i am commenting all the data so you can see the if there is no data present in the FlatList data source then it will automatically call the ListEmptyComponent=() prop and execute the function called inside it.

Comments
  • @Li357 ... and persistent if the data is unchanged. Random keys will cause rerendering every item on every data change, which would be very inefficient.
  • {item.name} did not work. But {item.item.name} worked for me. May be because I given (item) instead of ({item}) in renderItem. Thanks @Raymond
  • Because of the curly braces. If you're going to use curly braces you need to add a return statement.
  • This may not work. After deleting and adding some elements, it started to display duplicated items. I think the purpose of keyExtractor is to uniquely an item. Ideally you should have an unique id for each item and use the the id as the key. e.g. keyExtractor={item => item.id}
  • @JustWonder - right; if your list is going to have items removed, you can't use the index as a key, and you have to find another way of generating a unique key for each item. For the case where stuff is only ever added, this approach is fine.
  • the returned index has to be a string: keyExtractor={(item, index) => index.toString()}
  • or keyExtractor={ ( item, index ) => `${index}` }
  • Upvoted this solution. It helped me :p
  • Keys are supposed to be unique.Using random string is not a good idea. As mentioned above, it will cause unrequired re-rendering since the random function returns a different value if react tries to re-render due to any other change.
  • I hear you dude thanks for that. But how else would you get a unique string, what if you have like 5 flatlists