In this tutorial, we'll se how to use the FlastList component in React Native to display a virtualized list of the data fetched in the previous part. We'll also see how to use keyExtractor to add unique keys for each list item.
FlatList is an implementation of VirtualizedList which makes virtualization for improving the memory consumption and performance of large lists by maintaining a finite render window of active items and replacing all items outside of the render window with appropriately sized blank space.
According to the docs :. The FlatList component displays a scrolling list of changing, but similarly structured, data.
FlatList works well for long lists of data, where the number of items might change over time. Unlike the more generic ScrollViewthe FlatList only renders elements that are currently showing on the screen, not all the elements at once. You need to pass the data and renderItem props to FlatList :. The article will be passed as a prop. Using destructuring assignmentwe unpack the titleand description properties from the article object.
Read the reference for more info about FlatList. VirtualizedList: missing keys for items, make sure to specify a key property on each item or provide a custom keyExtractor. This simply says that we need to specify a unique key for each item in the list.
We can use a custom KeyExtractor for the FlatList as follows:. See this link for more information. According to the docs : The FlatList component displays a scrolling list of changing, but similarly structured, data. You need to pass the data and renderItem props to FlatList : data represents the source of data that will be displayed in the list, renderItem takes one item from the source and returns a formatted component to render.
Sponsored Links. Let's stay connected!Microsoft Program Manager by day; Mobile Developer by night. The actual implementation of master-detail is shockingly simple more on that later. However, I bumped into some specific issues when I was implementing it. The first of these was covered last time — how to detect orientation changes in React Native. The next is this. How do I implement swipe-right so that I can add a swipe-to-delete function to a FlatList.
Let me explain a little further. The latest edition of React Native has updated the list handling. ListView is or will be deprecated. This is great. I no longer have to implement a data source. All I have to do is pass the data I want to render to the FlatList and a rendering function and I am done.
There is also another component — the Swipeout — that implements swiping. However, it does it for ListView, which is deprecated. So no joy there. Or so I thought. I have two components — a NoteList. I want a few events to fire on the NoteList. These will then effect a scene change or a data update as needed. There are a couple of rules to keep in mind:. The first rule means you need to handle an onPress event in the NoteListItem renderer which is then picked up by the list item.
Here is my NoteListItem. I also wrap the View which is a native component in the TouchableHighlight so that my entire view is clickable. This makes the entire row clickable if we define an onPress event handler. This is all fairly basic FlatList code. If you use a simple application, like this:.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. However I have a toggle button that toggles the display of this list. That is, when true, it shows the items at the lowest price, and when false, it shows the original list. The problem is that when I press the toggle button the first time, it changes its state to true and organizes the list by price.
But when I press it again it changes the state to false, but it keeps showing the list organized by price. I've tried everything to make this switch, but I can't. Can someone help me by showing me where it's wrong? Sorting an array will mutate the existing array. So if toggleFilter is true you are permanently changing what's in Productsthen rendering it.
When you flip toggleFilter to false, you use Products as it is, but due to the previous renders it is now a sorted array. For performance reasons, you may want to memoize the sorting instead of sorting every time you render. That can be done with useMemo this:. Learn more. Sorting the items in the flatList. Asked today. Active today. Viewed 21 times. I have a list of products that is rendered in a Flatlist. My code: import Products from '.My previous post was about writing my first mobile app with React Native and getting it up on the Google Play Store for beta testing.Scroll Load More using Flatlist in React Native
I understand that getting an app accepted on the Apple Store is considerably harder, so I will wait until I get a bit of user feedback from the Android community before I attempt that. In that post I promised to write additional posts about various problems I encountered and how I dealt with them. I will start with a performance problem since it is still very fresh. My app lets you search for movies by title.
So my first attempt filled a list with the first ten titles from a query, then rendered a set of pager buttons at the end of the list. The user could press the "Next" button to request another ten titles. Once the next set was displayed, the user could continue forward or go backward.
There were also buttons to fast-forward to the last page, or rewind to the first page. The result looked like this:. Because a list of ten film titles wouldn't fit on my phone's screen after the header, I wrapped the entire screen in a ScrollView component.
Since I was just getting started and trying to make sure everything worked, I did not even bother to request enough titles to fill a screen on a larger device, such as a tablet.
Adam Navarrofrom the Expo support community, saw my app in the Expo app database when I asked a question, and suggested that I replace the pager buttons with a continuously refreshing, or "infinite", scrolling list. In other words, when the user enters a new query, the app makes enough requests to fill the screen on whatever device its on, then makes additional requests whenever the user attempts to scroll past the end of what's already been loaded, until all available results are exhausted.
The FlatList was surprisingly easy to use. At the minimum, you give it an array of items, and a method or component to render each item. Optionally, you can pass it a keyExtractor method that will tell it how to obtain a unique key for each list item. Otherwise, your renderItem method or component will have to do that. Since the key property is used only for React bookkeeping and has no bearing on how each list item actually gets rendered, I chose to pass a keyExtractor property to handle it that would be separate from the renderItem method.
That's just how I understand Separation of Concerns. So my FlatList now looks like this:. But there is more goodness in a FlatList. I assigned it a header component that renders a search bar and displays a little message about how many items were found.
I assigned it a footer that shows an animated spinner, or "activity indicator" graphic, whenever the app is loading more items to append the the end of the list, if visible.
Otherwise, the footer remains empty. The code now looks like this:. But I wasn't done yet. When the user scrolls to the end of the first ten items it has already fetched and rendered, we want the app to go back more more. It makes a remote request to omdbapi. If all goes well, a response comes back with ten more titles that we append to the list.
So the code now looks like this:. So now whenever the user scrolls to the end of the current list, it will automatically fetch and append more items to the list, as long as there are more items to fetch. In fact, some console. In fact, it seems to begin fetching additional pages even before the last item is visible when it is within a certain distance of being visible.More complex example demonstrating PureComponent usage for perf optimization and avoiding bugs.
For simplicity, data is just a plain array. If you want to use something else, like an immutable list, use the underlying VirtualizedList directly. A marker property for telling the list to re-render since it implements PureComponent. If any of your renderItemHeader, Footer, etc. Remember to include separator length height or width in your offset calculation if you specify ItemSeparatorComponent. How many items to render in the initial batch. This should be enough to fill the screen but not much more.
Note these items will never be unmounted as part of the windowed rendering in order to improve perceived performance of scroll-to-top actions. 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. Items should all be the same height - masonry layouts are not supported. Called once when the scroll position gets within onEndReachedThreshold of the rendered content.
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. Thus a value of 0. If provided, a standard RefreshControl will be added for "Pull to Refresh" functionality. Make sure to also set the refreshing prop correctly. Called when the viewability of rows changes, as defined by the viewabilityConfig prop.
Scrolls to the item at a the specified index such that it is positioned in the viewable area such that viewPosition 0 places it at the top, 1 at the bottom, and 0.
Requires linear scan through data - use scrollToIndex instead if possible. May be janky without getItemLayout prop. Tells the list an interaction has occured, which should trigger viewability calculations, e.
This is typically called by taps on items or by navigation actions. You can edit the content above on GitHub and send us a pull request! React Native 0. FlatList A performant interface for rendering simple, flat lists, supporting the most handy features: Fully cross-platform.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. It seems like FlatList renders all items at once even though the cell isn't actually visible on the screen.
Setting 30 items and seems like 'rendered' warning was called according to the total number of the items. I thought FlatList is similar to the way RecycleView in Android works, render an item only when it's about to be visible on the screen.
Am I missing something? Won't it decrease performance? I wished it could render an item only when it's about to be shown. Same as the Thread-Opener, at first, my Flatlist render only the amount of renders I defined in initialNumToRenderbut immediately after that, the app starts to render the whole rest of the List. I use native-base. A FlatList inside of a ScrollList will pipe you to strange results. In order to constrain memory and enable smooth scrolling, content is rendered asynchronously offscreen.
This means it's possible to scroll faster than the fill rate ands momentarily see blank content. This is a tradeoff that can be adjusted to suit the needs of each application, and we are working on improving it behind the scenes. This is a PureComponent which means that it will not re-render if props remain shallow- equal.
Make sure that everything your renderItem function depends on is passed as a prop e. This includes the data prop and parent component state. FlatList renders too many items in advance to get better fill rate. We have similar issues. We build RecyclerListView to workaround such problems.
Very similar to RecyclerView but it is JS only. It is faster than FlatList and battle tested at Flipkart. You can try it. Learn more. ReactNative FlatList render all items at once? Ask Question. Asked 2 years, 8 months ago. Active 6 months ago. Viewed 10k times.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
Already on GitHub? Sign in to your account. We are using FlatList to render Message Items and after the Flatlist has been rendered we are using scrollToBottom to go to the last item.
Implementing swipe-right on a React Native FlatList
The Flatlist is working without any issues when having about 20 items, but when we have many items it is NOT always rendering them and not display them at all. We are having an example with 80 items and sometimes is rendering all of them but most of the times is rendering about No it does not render at all. But it is doing the following when is not rendering all items, it shows a white space but when i touch it, it aligns properly to the last item but the rest not rendered and never shown.
I solved my problem: Never mutate or map over your props for list items. There is a HUGE performance difference when you implement a customized shouldComponentUpdate function with each of your entries - assuming they are various React Components you are rendering.
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Maybe the issue has been fixed in a recent release, or perhaps it is not affecting a lot of people. If you think this issue should definitely remain open, please let us know why. Thank you for your contributions. Hi, I'm running react-native v0. Will this be fixed? I am having a similar issue, but not even on large lists, sometimes it just only renders partial rows, and the rest of the data are all just blank which you can clearly see that the list left some blank space for the rest of the data, but just not rendering them.
This just happens sometimes, most of time it works perfect, very hard for me to find out where excatly went wrong. It does seem to render, the jumping of next batch being rendered is visible but at some point it just cuts off.
The space is reserved but nothing is visible.
In fact, inspecting it react views shows the space. Everything is in the tree, it just doesn't show or shows transparent. Note: When making the items considerably smaller 20 height the entire list does render. So it looks like there's some sort of cut-off point. RWOverdijk this worked, thanks.
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I was having the same issue with long lists on ios. I have list items that can display more items on a button click. Switching ios over to ListView fixed the display issue. I decided to use ScrollView and rendering the list of items and header by myself, I know that this can have some performance problems but it works for me now.
I solved the issue by removing flex style property from the container of renderItem.
React Native: How to use FlatList
If it's a performance problem caused by listview You can try this library react-native-nlist. Quite what is going on to cause such a difference in the performance of this element between debug and non-debug mode where other elements seem to have no issue, I'm not sure.
I wonder if it's related to time differences between host and emulated system - see