Flatlist getitemlayout.

Flatlist getitemlayout Maybe a correct/precise implementation (calculation of length and offset) of getItemLayout() function is needed. offset: The distance (in pixels) of the current row from the top May 11, 2023 · Let's discuss some ways to optimize FlatList for better performance. You can set the getItemLayout to your FlatList component. Using Real Android Device; As you see below when my app is running on RTL direction FlatList automatically scrolls to top/first of the list but LTR Jul 5, 2023 · Ques: Is FlatList scrollable? Ans: FlatList provides scrollable features by default. forceRTL(true) Make my renderItem component extend as PureComponent. Jul 1, 2024 · Use getItemLayout: If your items have a fixed height, Optimizing FlatList and SectionList in React Native is crucial for handling large datasets efficiently. Adding getItemLayout can be a great performance boost for lists of several hundred items. Examples of Use-Cases FlatList in real life. 如果所有列表项组件都具有相同的高度（或宽度，对于水平列表），则提供 getItemLayout 属性将消除 FlatList 管理异步布局计算的需要。这是一种非常理想的优化技术。 Jun 7, 2017 · B. selected變化時，能夠正確觸發FlatList的更新。如果不指定此屬性，則FlatList不會觸發更新，因為它是一個PureComponent，其props在===比較中沒有變化則不會觸發更新。 Oct 29, 2020 · If you are using a FlatList in React Native, there’s a chance you will want to use the scrollToIndex function to scroll to a certain item’s index. You can use this code to achieve other use cases of programmitically scrolling flatlist. It should bahave the same way. I attempted to create a simple FlatList implementation - just data and required props, foremost. Oct 10, 2024 · Esto permite a FlatList omitir la medición de los ítems y calcular directamente la posición y el tamaño de los ítems y las separaciones, lo que resulta en un desplazamiento mucho más fluido y tiempos de carga más rápidos. 5. getItemLayout={(data, index) => ( {length: 行高, offset: 行高 * index, index} )} /getItemLayout是一个可选的优化，用于避免动态测量内容尺寸的开销，不过前提是你可以提前知道内容的高度。如果你的行高是固定的，getItemLayout用起来就既高效又 I'm using a FlatList where each row can be of different height (and may contain a mix of both text and zero or more images from a remote server). According to Reactive FlatList documentation: getItemLayout is an optional optimizations that let us skip measurement of dynamic content if you know the height of items a priori. Jan 4, 2018 · FlatList属性（函数）： 1. 69. ; key: string: Optional key to keep track of section re-ordering. getItemLayout (data, index) => {length: number, offset: number, index: number} getItemLayout est une optimisation facultative qui permet d'ignorer la mesure du contenu dynamique si vous connaissez à l'avance la taille (hauteur ou largeur) des éléments. getItemLayout is both efficient and easy to use if you have fixed height items, for example: getItemLayout={(data, index) => ( {length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index} )} Additionally, the only real documentation for getItemLayout is on the FlatList page, and that doesn't help much when you're trying to figure out how to calculate the offset for a SectionList. To get started with FlatList, you’ll first need to import it from the ‘react-native’ package. The issue with that is, the flatlist needs to implement a function to calculate the offset for every element. getItemLayout={(data, index) => ({ width: 300, //- Here offset: 300 * index, index, } )} May 11, 2021 · 如果你的行高是固定的，getItemLayout用起来就既高效又简单，类似下面这样： getItemLayout = { (data , index ) = > ( {length : 行高 , offset : 行高 * index , index } ) } 注意如果你指定了SeparatorComponent，请把分隔线的尺寸也考虑到offset的计算之中。 Jan 30, 2022 · 滚动到底部。如果不设置getItemLayout属性的话，可能会比较卡。 scrollToIndex: 滚动到指定index的item。如果不设置getItemLayout属性的话，无法跳转到当前可视区域以外的位置。 scrollToItem: 滚动到指定item，如果不设置getItemLayout属性的话，可能会比较卡。 scrollToOffset: 滚动 使用 getItemLayout . I cant think of a way to pre-render the flatlist and get the height of every item in it. I cannot use getItemLayout because I don't know the height of each row (nor the previous ones) to be able to calculate. Here is working code example (tested on iOS). getItemLayout . But you can use this method only if your list items have a fixed height. Ques: How to display data from an API using FlatList? Ans: To display data from an API using React Native FlatList, you can use the fetch API to request Apr 14, 2025 · array: The data for rendering items in this section. If you don't plan on re-ordering sections, the array index will be used by default. const content = useMemo<JSX. . But this was just happening on RTL. Flatlist renders text items so I tried to get different heights for items depending on their content: Jun 13, 2023 · React Native’s FlatList is designed to be performant right out of the box. state}屬性，是為了保證state. You signed out in another tab or window. May 10, 2025 · FlatList is a React Native component that is a scrolling list that shows changing information while keeping the same look. 9版本 onViewableItemsChanged方法 在多次取viewableItems中index的时候 会出现不准确的情况，我的Item是一个占一屏并且设置了pagingEnabled在这种情况下 ， 我采用了onMomentumScrollEnd方法去获取滑动的距离，以及测量item的高度去计算 Oct 29, 2023 · getItemLayout 屬性. Array of objects, much like FlatList's data prop. As you can see from the graphs, the performance is fairly similar and it is hard to come up with a conclusion about what is better to use. React Native: App gets stuck when using FlatList. This is where the react-native-get-item-layout-section-list package comes in. But the method is not working as expected and is scrolling to wrong position. Apr 14, 2025 · getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. Related. 66. Reload to refresh your session. By the result of this, sometimes when you scroll fast enough, you will see some gaps in the list. You can also pass in that data in getItemLayout. Jul 25, 2018 · I'm using a flatList to render items from a json file, I want to scroll to a specific index when a button is pressed, I declared the function for button press as below goIndex = () =&gt; { this. getItemLayout是一个可选的优化，用于避免动态测量内容尺寸的开销，不过前提是你可以提前知道内容的高度。如果你的行高是固定的，getItemLayout用起来就既高效又简单，类似下面这样： May 18, 2020 · 在源码中（#L1287、#L2046），如果不使用 getItemLayout，那么所有的 Cell 的高度，都要调用 View 的 onLayout 动态计算高度，这个运算是需要消耗时间的；如果我们使用了 getItemLayout，VirtualizedList 就直接知道了 Cell 的高度和偏移量，省去了计算，节省了这部分的开销。 RN FlatList的item高度不定时，如何精准定位 案例： 界面上部分横向滚动(Scrollview)的标题，下部分是内容列表(FlatList)，但是由于 flatlist 的item 高度不定，无法准确使用getItemLayout计算高度，导致无法使用scrollToIndex以及scrollToItem定位方法，而我的需求是：点击上部分的某个标题能准确跳转到某一个 item。 Sep 20, 2023 · The configuration and optimization of the props: Both VirtualizedList and FlatList have several props that can help to improve the performance, such as removeClippedSubviews, maxToRenderPerBatch 通过传递extraData={this. getItemLayout={(data, index) => ({ width: 300, //- Here offset: 300 * index, index, } )} May 16, 2023 · The FlatList is configured with a windowSize of 4 and with a getItemLayout respecting the documentation. 1. ListView and FlatList are two popular components used to render Jul 8, 2018 · Eventually I found I need to pass the height of the header into the getItemLayout offset. getItemLayout. This is a very desirable optimization technique and if your components have dynamic Jul 5, 2019 · I am implementing a FlatList with initialScrollIndex and getItemLayout. Unfortunately, this function is a lot easier to use with fixed item heights where it is easy to implement the required getItemLayout function. FlatList numColumns doesn't appear to be working correctly? 0. 59. 5w次，点赞11次，收藏22次。前言在上一篇博客中了解了列表组件的相关内容，主要是静态的展示了一个列表数据，了解了ScrollVIew，FlatList和SectionList的基本用法，本篇文章就深入的了解一个常用的一个列表组件FlatList的用法！ FlatList scrollToIndex Example. FlatList shows item 0 at the top of rendered list. I'm using a FlatList where each row can be of different height (and may contain a mix of both text and zero or more images from a remote server). FlatList是基于VirtualizedList的，要说FlatList的特性还要从VirtualizedList说起： VirtualizedList Vritualization 通过维护一个有限的渲染窗口（其中包含可见的元素），并将渲染窗口之外的元素全部用合适的定长空白空间代替的方式，极大的改善了内存消耗以及在有大量数据 使用 getItemLayout . This is a very desirable optimization technique. Actual Results. To scroll to locations outside the render window we need to specify the getItemLayout prop. What I am attempting to do is There is a good article that explains the getItemLayout, please find it here. 61. So maybe if you want to track the size of each item you can store that data in the flatlist and pass it into getItemLayout as it renders – Aug 16, 2023 · When it comes to rendering large lists efficiently in React Native, the FlatList component is a go-to choice. This is Snack Expo Example Apr 6, 2022 · I have a FlatList inside useMemo as follows. Not sure why they need the index as that doesn't change. I also faced data[index] as undefined. we will also be needing total itemWidth Nov 4, 2020 · scrollToIndex should be used in conjunction with getItemLayout or onScrollToIndexFailed, otherwise there is no way to know the location of offscreen indices or handle failures. Try add initialNumToRender prop on your FlatList. 0. Because the text in each row is of variable length, I cannot provide a static height for use in getItemLayout. allowRTL(true) Set I18nManager. Not using getItemLayout() solved the issue for me. Nov 6, 2020 · However to use scrollToOffset I have to use getItemLayout but using it makes my flatlist buggy. As you quickly find out as you start using these new list classes, this prop is vitally important if you want a half-way decent user experience. These lists take a getItemLayout prop that it uses to calculate dimensions for the things on your list. I can pass any value for length offset and index, and it will have no effect on the layout of the list. 43版本推出FlatList替代ListView，FlatList实现继… May 25, 2017 · RN 0. It loads items that are currently visible on the screen and removes these items as they go off the screen. I tried to use getItemLayout but my flatlist items have different height, how can i fix this? getItemLayout={(data, index) => ( {length: 40, offset: 40 * index, index} )} getItemLayout (data, index) => {length: number, offset: number, index: number} getItemLayout 是一项可选优化，如果您提前知道项目的大小（高度或宽度），则可以跳过动态内容的测量。如果您有固定大小的项目，则 getItemLayout 非常有效，例如： getItemLayout is an optional optimization that let us skip the measurement of dynamic content if you know the height of items ahead of time. getItemLayout is an optional optimization that let us skip the measurement of dynamic content if you know the height of items ahead of time. getItemLayout is the most efficient, and is easy to use if you have fixed height items, for example: May 18, 2018 · 困扰两个星期的问题，在这里记录一下： 首先提一下FlatList的坑，目前使用的0. getItemLayout is efficient if you have fixed size items, for example: Sep 9, 2021 · If you don't provide getItemLayout function as props, Flatlist have to calculate height for every item in the list. 44. But when I use getItemLayout to improve performance, the list doesn't load more elements behind. Without getItemLayout, onViewableItemsChanged seems to happily rely on the actual layout, whereas if getItemLayout is set, it appears to use that calculation. js This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. Nov 14, 2017 · ReactNative 之FlatList踩坑封装总结. 5 React-native FlatList items not get to right height. Consistently does nothing on both iOS simulator and Android emulator React Native version 0. Ejemplo de getItemLayout para ítems de tamaño fijo: Dec 15, 2017 · @JakubSzczepanik It still scrolls to that index regardless the size of the individual comment items. Used to Aug 11, 2017 · 如官方所言，使用这两个函数的时候，最好指定设置getItemLayout属性。 使用. Le getItemLayout est efficace si vous avez des éléments de taille fixe, par exemple : FlatList example using scrollToItem & scrollToIndex. Setting Up FlatList. Feb 14, 2023 · I am working with a large list in React native, I using FlatList to show it. In response, you might search for optimization techniques online and experiment with various FlatList properties like Nov 23, 2017 · FlatList with getItemLayout(): Invariant Violation: Should not have to estimate frames when a measurement metrics function is provided #16950. Dec 10, 2019 · FlatList是基于VirtualizedList的，要说FlatList的特性还要从VirtualizedList说起： VirtualizedList Vritualization 通过维护一个有限的渲染窗口（其中包含可见的元素），并将渲染窗口之外的元素全部用合适的定长空白空间代替的方式，极大的改善了内存消耗以及在有大量数据 给FlatList指定extraData={this. getItemLayout is efficient to use if you have fixed height items, for example: getItemLayout = {(data, index) => ({length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index})} Nov 17, 2022 · I am trying to optimize a FlatList with getItemLayout, but the getItemLayout prop is not doing anything. I'm using FastImage to preload and cache the images before showing the list. state. getItemLayout is efficient if you have fixed size items, for example: Feb 8, 2018 · The three arguments to the getItemLayout callback are: length: Height of each individual row. This is because (a) React Native won Mar 27, 2019 · To make sure the auto-scroll animation to a certain index is smooth, we have to provide FlatList with a getItemLayout function. However, ensuring optimal performance requires understanding and applying a set of Jul 26, 2017 · ReactNative学习笔记十一之FlatList. Trying to tackle a potential problem area right off the bat (making performant, dynamic list items), I implemented and assigned the getItemLayout method. Sep 18, 2020 · Since FlatList is a PureComponent, it assumes that the data is an immutable object and that any change in data is done by setting a new data source object in the state object. FlatList. We will also use the useRef hook in this example. length + 2 (1 for section header and 1 for section footer), you can find the code here (RN-52). getItemLayout is the most efficient if you have fixed height items, for example: getItemLayout = {(data, index) => ({length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index})} Sep 25, 2019 · Added some data to my FlatList; Add horizontal={true} property to flatlist; Set I18nManager. Here is my code for Flatlist: <FlatList ref={flatRef} showsHorizontalScrollIndicator={false} horizontal data={data} renderItem={renderCell} /> May 16, 2023 · The FlatList is configured with a windowSize of 4 and with a getItemLayout respecting the documentation. Nov 14, 2018 · React Native FlatList getItemLayout for multiple columns. selected变化时，能够正确触发FlatList的更新。如果不指定此属性，则FlatList不会触发更新，因为它是一个PureComponent，其 props 在===比较中没有变化则不会触发更新。 keyExtractor属性指定使用 id 作为列表每一项的 key。 Jan 24, 2024 · The decision to use useCallback for functions like getItemLayout and ListHeaderComponent in a FlatList component depends on whether these functions have dependencies that might trigger unnecessary re-renders. After fetching the messages from my API, I call this. (See the code below) At first, when we scroll the first elements, we can see there is no issue but once we reach the 4th, we can notice some kind of glitch which is actually a repositioning. Element>( () => isLoading ? ( <Loader /> ) : !alerts. 前言. The optimizations work best when the height is constant. Everything is in App. As visible from the photos Sep 4, 2018 · 文章浏览阅读5. getItemLayout is efficient if you have fixed size items, for example: Sep 30, 2024 · getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. 这篇文章没有什么特别需要讲的,主要是之前在处理键盘遮挡问题的时候,使用到了flatlist中的滚动问题,所以特别记录一下. Closed getItemLayout is an optional optimization that let us skip measurement of dynamic content if you know the height of items a priori. data. If I remove the getItemLayout then FlatList still works as usual. state}，FlatList我们确保FlatList自己将在state. This is really useful! Using getItemLayout removes the need for FlatList to measure the list items layout. However, every time my app starts up, it renders the first elements somehow and then jumps to the actual initialScrollIndex. Premature optimization is the root of all evil! 🙂. providing the getItemLayout prop eliminates the need for May 19, 2020 · 优化FlatList列表性能方法我总结为三种： 1、getItemLayout 可选优化项。但是实际测试中，如果不做该项优化，性能会差很多。 但是实际测试中，如果不做该项优化，性能会差很多。 Jan 14, 2020 · FlatList方法： scrollToEnd（params?:object） 滚动到底部调用。如果 不设置getItemLayout属性的话，可能会比较卡。 scrollToIndex（params:object） 滚动到指定位置，如果不设置getItemLayout属性的话，可能会比较卡。 scrollToItem（params：object） Jul 21, 2017 · Saved searches Use saved searches to filter your results more quickly May 4, 2023 · Introduction. Sep 30, 2024 · getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. 這是 FlatList 的一個屬性，常用於優化。FlatList 需要事先渲染過一次，動態獲取渲染尺寸之後再真正渲染到頁面中，如果事先知道列表中的每一項高度就能使用 getItemLayout 减少一次渲染。 My issue here was that scrollToEnd() worked fine on mobile but on web it always scrolled to the top. If all your list item components have the same height (or width, for a horizontal list), passing this prop removes the need for your FlatList to dynamically calculate it every time. 当 FlatList 组件需要滚动到特定位置时，会重新渲染初始位置和目标位置之间的所有列表项，这将会导致滚动性能的问题。为此，我们可以通过使用 getItemLayout 方法预设列表项的高度和偏移量，来避免不必要的重新渲染。 示例代码 إذا لم تُعيَّن هذه الخاصية فلن يعلم مكوّن FlatList أنه يحتاج إلى الخاصية getItemLayout هي تحسين Sep 14, 2019 · I had the same issue. 如果单元行的高度是可知的，那么实现getItemLayout接口对于性能优化有很大的好处，因为不用在渲染时临时计算每个单元行的尺寸 Dec 31, 2024 · 使用 getItemLayout 优化滚动性能. length ? Feb 6, 2019 · 我有一个FlatList，它填充了大约18000行文本。因为每一行中的文本长度是可变的，所以我不能在getItemLayout中提供静态高度。 我尝试做的是首先使用一个虚拟视图迭代整个数据集，我通过onLayout从这个视图中收集高度维度。 May 19, 2019 · FlatList是基于VirtualizedList的，要说FlatList的特性还要从VirtualizedList说起： VirtualizedList Vritualization 通过维护一个有限的渲染窗口（其中包含可见的元素），并将渲染窗口之外的元素全部用合适的定长空白空间代替的方式，极大的改善了内存消耗以及在有大量数据 Jan 21, 2018 · React Native 踩坑日记(十) —— 使用 flatlist 的滚动处理键盘遮挡的问题. I would think this should be width rather than length because you are rendering a horizontal FlatList. With 50 items it's working fine but with 3000 items I'm not being able to scroll after first 200-300 items. 用于渲染基本平面列表的高性能接口，支持最便捷的功能 getItemLayout 是一种可选的优化，如果您提前知道项目的 Apr 2, 2019 · 列表视图在app中是非常常见的，目前React Native比较严重的性能问题集中在FlatList大列表等地方，以下通过js层的优化，甚至原生层的优化封装，使性能媲美原生。 React Native 0. Use getItemLayout Prop. getItemLayout is efficient if you have fixed size items, for example: Aug 9, 2023 · You signed in with another tab or window. Jan 1, 2018 · My FlatList cells contains text of different length, which leads to different height of each cell, which leads i can not return fixed value in getItemLayout. Apr 14, 2025 · Use getItemLayout If all your list item components have the same height (or width, for a horizontal list), providing the getItemLayout prop removes the need for your FlatList to manage async layout calculations. flatListRef. They can be of different heights, but the height should be static. But the most interesting part is that that would not 重要なデータを先読みするgetItemLayout. Aug 13, 2019 · My FlatList items are vary in size (height) which makes me unable to implement getItemLayout since this requires me to have prior knowledge about the FlatList item size, therefore I cannot use scrollToIndex (which requires getItemLayout to be implemented). Let’s create a basic setup for a list of items. selected变化时，能够正确触发FlatList的更新。如果不指定此属性，则FlatList不会触发更新，因为它是一个PureComponent，其 props 在===比较中没有变化则不会触发更新。 keyExtractor属性指定使用 id 作为列表每一项的 key。 Dec 10, 2018 · FlatList中有一个getItemLayout方法. 给FlatList指定extraData={this. 6k次。本文探讨了FlatList组件的性能优势，解释了它如何通过仅渲染可见内容提高效率。文章总结了三项关键优化技巧：1) 使用getItemLayout预先计算布局以减少渲染；2) 谨慎应用removeClippedSubviews以优化滑动性能；3) 结合PureComponent避免不必要的重渲染，并通过extraData确保状态更新。 Theres a few things you can try here. Expect item 50 to appear at the top of the rendered FlatList. Jul 1, 2024 · The FlatList indicates that it can’t render the list smoothly. Then you can use alignItems in order to have the card positioned in the middle or on the left - Unsure as to which you wanted here. Also there is some prop called Jul 7, 2020 · For this i have used scrollToIndex method of FlatList in conjunction with getItemLayout prop of FlatList and passed the index of the current podcast item being played to the method. To review, open the file in an editor that reveals hidden Unicode characters. 如果您的所有列表项组件都具有相同的高度（或宽度，对于水平列表），则提供 getItemLayout prop 可以消除 FlatList 管理异步布局计算的需要。这是一种非常理想的优化技术。 Scroll performance issues generally occur due to how React Native handles rendering and memory management. selected更改时重新呈现。没有设置这个道具，FlatList不知道它需要重新渲染任何物品，因为它也是一个PureComponent，并且道具比较不会显示任何变化。 FlatList#getItemLayout は、リストのスクロールパフォーマンスを大幅に向上させる強力なツールですが、複雑なレイアウトや動的なデータの場合、実装が困難になることがあります。このような場合には、以下の代替方法を検討することができます。 Oct 30, 2018 · scrollToIndex should be used in conjunction with getItemLayout or onScrollToIndexFailed. getItemLayout is efficient if you have fixed size items, for example: Sep 6, 2023 · FlatList with getItemLayout. 之前使用的组件是ListView，当时要添加一个下拉刷新，上拉加载的功能，所以对ListView做了一些封装，但是后来看官方文档，不建议再使用ListView，因为效率问题，做过Android的朋友都知道，Android的ListView如果不自己处理一下，也是有效率问题的。 Jun 18, 2022 · A guide to analyzing your Flatlist performance, identifying the bottleneck, and fixing common issues. 3 使用 getItemLayout ¥Use getItemLayout. extraData={selectedId} を FlatList に渡すことで、状態が変わったときに FlatList 自体が再レンダリングされるようになります。 このプロパティを設定しないと、 FlatList は PureComponent であるため、アイテムを再レンダリングする必要があることを認識できず May 20, 2018 · In this answer I have mentioned a very easy code snippet where there are 2 buttons to scroll flatlist right or left. I am using React Native 0. function. May 17, 2017 · As stated in above comment, getItemLayout should resolve your issue. create a FlatList with 100 items, to many to fit on a page; call this. Aug 31, 2017 · Hey, I've just run to a similar problem: the FlatList w/ getItemLayout would render the initialNumToRender and then have a blank space below related to the additional items not being rendered. Using getItemLayout in FlatList brings some good performance benefits in my experience. getItemLayoutを使用すると、各アイテムの高さが固定の場合に、効率的なスクロールが可能になります。リストのレンダリング時に計算を省略するため、パフォーマンスが向上します。 Jun 26, 2017 · React Native’s old ListView was superseded by the new FlatList and SectionList in version 0. scrollToIndex() is a method of FlatList that can scroll to the item at the specified index. And when I removed getItemLayout it would render the additional items but only after scrolling. Use getItemLayout to optimize flatlist react native. Here are a few examples of how you could potentially use Jul 23, 2023 · Use getItemLayout. Jul 27, 2018 · Have you tried changing the properties of the returning object within getItemLayout from length: 300 to width: 300. When you start playing around with the new Nov 14, 2018 · React Native FlatList getItemLayout for multiple columns. Sep 30, 2022 · I'm trying to find a workaround for initialScrollIndex in flatlist which is not working properly, I used getItemLayout to fix that, but the problem is that my elements inside the flatlist don't hav getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. I've solved this with setting: onContentSizeChange which will handle scroll to index whenever flatlist data is changed and all items rendered ( you can handle how many items will be rendered on initial render with setting initialNumToRender if needed) Jan 21, 2018 · React Native 踩坑日记(十) —— 使用 flatlist 的滚动处理键盘遮挡的问题. Nov 23, 2023 · 在 React Native 中，FlatList 是一种非常常用的列表组件。它可以高效地渲染大量数据，并且支持滚动加载数据。但是，当渲染大数据量时，FlatList 的性能也会受到影响。本文将介绍一些优化技巧，以提高 FlatList 渲染大数据量时的性能。 Jan 27, 2018 · I am trying to create a chat in React native using a &lt;Flatlist /&gt; Like WhatsApp and other chat apps, the messages start at the bottom. 給FlatList指定extraData={this. Nov 19, 2024 · 什么是 FlatList？ FlatList 是 React Native 中的一个内置组件，用于呈现长列表数据。通过使用 FlatList，我们可以避免一次性渲染大量数据所带来的性能问题。FlatList 可以逐个渲染列表项，并在滚动时动态加载和卸载列表项，从而提高渲染性能。 如何使用 FlatList？ Apr 17, 2024 · getItemLayout是FlatList的一个属性，它允许组件预知每一个列表项的大小，进而提高滚动和跳转的效率。 减少计算量 ：当组件知晓每个项的尺寸后，可以在不实际渲染的情况下计算出任意位置的偏移量，这样可以在跳转或滚动时大大减少计算量。 Sep 11, 2023 · FlatList provides several key features, such as lazy loading, item recycling, and smooth scrolling, making it ideal for building performant lists in your mobile applications. A) Setting a pre-defined width for the card ( Maybe equal to the height you've set? ). 因为这两个是FlatList组件的函数，所以在使用这两个函数之前，首先我们要得到FlatList组件的引用。 这时候就需要ref属性。react提供的这个ref属性，表示为对组件真正实例的引用。 May 7, 2021 · for initial rendering its better to use initialScrollIndex instead of scrollToIndex, have to use getItemLayout in addition to that as follows: const getItemLayout = (data, index) => { return { length: screenWidth, offset: screenWidth * index, index, }; }; get the screenWidth from dimensions prop from react natie 如果你有固定尺寸的物品，getItemLayout 会很有效，例如： ¥getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. getItemLayout is efficient if you have fixed size items, for example: Jul 6, 2023 · 实际生产中，如果你不填getItemLayout属性，不把列表项的高度提前告诉FlatList，让FlatList通过onLayout的布局回调动态计算，用户时可以感觉到滑动变卡的。因此，如果你使用FlatList，又提前知道列表项的高度，我建议你吧getItemLayout属性填上 Feb 7, 2019 · I have a FlatList which fills with about 18000 text rows. My strategy is: My strategy is: On load, iterate through dataset for list and calculate height of each row Flatlist getItemLayout usecase. 中文网是这么介绍的. Efficient list rendering is crucial in React Native applications to ensure smooth scrolling and improve performance. You switched accounts on another tab or window. Try use getItemLayout to skip measurement of dynamic content. Jun 26, 2017 · Like FlatList, its simpler cousin, SectionList takes a getItemLayout prop that you can use to tell it about the dimensions of the stuff on your list. I can't find any issues or documentation on this, so not sure if the behaviour was intentional. Apr 29, 2020 · Use getItemLayout This method is highly desirable as this will certainly cut out the needs for FlatList to run some asynchronous layout calculation processes if we have defined the height for each . isChanged} prop to re-render a FlatList component by updating the value of isChanged property. Feb 26, 2022 · React-Native Flatlist getItemLayout with dynamic item height. The idea is the FlatList just needs to know for this index, how tall is it (length), how do I jump to it (offset) and pass back the current index. 如果您的列表项组件都具有相同的高度（或宽度，对于水平列表），则提供 getItemLayout属性可以消除您的 FlatList 管理异步布局计算的需要。这是一种非常理想的优化技术。 Apr 30, 2021 · How do I implement the getItemLayout prop correctly on my FlatList? I understand this is suppose to tell the FlatList the height of each item to make it more performant. 6 Apr 13, 2018 · The issue I am running into is that the items the flatlist renders have a minHeight. 5. 0 -Description FlatList uses scrollToIndex to scroll to the last few elements, and the element leaves the bottom of the list. If all your list item components have the same height (or width, for a horizontal list), providing the getItemLayout prop removes the need for your FlatList to manage async layout calculations. By providing our own getItemLayout function, it won't have to calculate every item's height and the performance will improve. state}属性，是为了保证state. The versatility of the FlatList component makes it suitable for a range of applications in React Native projects. 2. The reason is that index is calculated considering section. getItemLayout is efficient to use if you have fixed height items, for example: getItemLayout = {(data, index) => ({length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index})} There is a good article that explains the getItemLayout, please find it here. Alternatively, use the extraData={this. 43 last year. However how am I to find out the size of each item? FlatList ¶ Компонент getItemLayout эффективен, если у вас есть элементы фиксированного размера Sep 20, 2022 · 文章浏览阅读2. With SectionList we have to be very careful while processing index. Jun 22, 2021 · 次に getItemLayout ですが、こちらは FlatList に表示する要素の高さが固定の場合にかなり有効とのことです。 レイアウトの計算を管理する必要がなくなるため、最適化に有効らしいです。 Jun 14, 2017 · Using RN 0. As you can see I am simply adding a static number for the 使用 getItemLayout . js file. Here are the primary reasons: Over-rendering: React Native lists, like FlatList or SectionList, can re-render frequently if not optimized, leading to unnecessary component updates. scrollToIndex({animated: true, index: 50} Expected Results. And when scrolling to the last element, it is reported scrollToIndex should be used in conjunction w Nov 8, 2022 · 注意：如果不指定 getItemLayout 属性，则无法滚动到渲染窗口之外的位置。 在 Android 的 FlatList (React Native) 中隐藏滚动条 5. I have a FlatList that renders similarly to yours (it has a list of 50 images at any given time, each image is roughly the size of an iPhone SE) Oddly enough we are not using getItemLayout(). The getItemLayout property allows React Native to avoid the measurement process, which can Mar 15, 2022 · Calculate getItemLayout length and offset in horizontal lists. For my case it was caused by getItemLayout() in FlatList. Snack, code example, screenshot, or link to a repository: minimal snack example Dec 20, 2018 · getItemLayout is the most efficient, and is easy to use if you have fixed height items. Probably because I have elements with different size in the FlatList and couldn't define getItemLayout. 在RN中FlatList是一个高性能的列表组件，它是ListView组件的升级版，性能方面有了很大的提升，当然也就建议大家在实现列表功能时使用FlatList,尽量不要使用ListView，更不要使用ScrollView。既然说到FlatList，那就先温习一下它支持的 Nov 12, 2023 · getItemLayout is an optional optimization that allows skipping the measurement of dynamic content if you know the size (height or width) of items ahead of time. jlvooc vgrvro ajimkse pwsqj qxxo mucwbvk qmhhk cde upohh tazxbm