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<script src="https://snack.expo.io/embed.js" defer="defer"></script><title data-react-helmet="true">Optimizing Flatlist Configuration · React Native</title><meta data-react-helmet="true" property="twitter:image" content="https://reactnative.dev/img/logo-og.png"><meta data-react-helmet="true" name="twitter:image:alt" content="Image for React Native"><meta data-react-helmet="true" name="docsearch:language" content="en"><meta data-react-helmet="true" name="docsearch:version" content="0.63"><meta data-react-helmet="true" name="docsearch:docusaurus_tag" content="docs-default-0.63"><meta data-react-helmet="true" property="og:image" content="https://reactnative.dev/img/logo-og.png"><meta data-react-helmet="true" name="twitter:card" content="summary"><meta data-react-helmet="true" name="twitter:image" content="https://reactnative.dev/img/logo-og.png"><meta data-react-helmet="true" property="og:title" content="Optimizing Flatlist Configuration · React Native"><meta data-react-helmet="true" name="description" content="Terms"><meta data-react-helmet="true" property="og:description" content="Terms"><meta data-react-helmet="true" property="og:url" content="https://reactnative.dev/docs/optimizing-flatlist-configuration"><link data-react-helmet="true" rel="shortcut icon" href="/img/favicon.ico"><link data-react-helmet="true" rel="preconnect" href="https://BH4D9OD16A-dsn.algolia.net" crossorigin="anonymous"><link data-react-helmet="true" rel="canonical" href="https://reactnative.dev/docs/optimizing-flatlist-configuration"><link rel="stylesheet" href="/styles.fccefeba.css">
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href="/docs/running-on-simulator-ios">Running On Simulator</a></li><li class="menu__list-item"><a class="menu__link" tabindex="-1" href="/docs/communication-ios">Communication between native and React Native</a></li><li class="menu__list-item"><a class="menu__link" tabindex="-1" href="/docs/app-extensions">App Extensions</a></li></ul></li></ul></div></div></div><main class="docMainContainer_1rYT"><div class="container padding-vert--lg docItemWrapper_1Hme"><div class="row"><div class="col docItemCol_2AGf"><div class="docItemContainer_1tAC"><article><header><h1 class="docTitle_cWlf">Optimizing Flatlist Configuration</h1></header><div class="markdown"><h2><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="terms"></a>Terms<a aria-hidden="true" tabindex="-1" class="hash-link" href="#terms" title="Direct link to heading">#</a></h2><ul><li><p><strong>VirtualizedList:</strong> The component behind <code>FlatList</code> (React Native's implementation of the <a href="https://bvaughn.github.io/react-virtualized/#/components/List" target="_blank" rel="noopener noreferrer"><code>Virtual List</code></a> concept.)</p></li><li><p><strong>Memory consumption:</strong> How much information about your list is being stored in memory, which could lead to an app crash.</p></li><li><p><strong>Responsiveness:</strong> Application ability to respond to interactions. Low responsiveness, for instance, is when you touch on a component and it waits a bit to respond, instead of responding immediately as expected.</p></li><li><p><strong>Blank areas:</strong> When <code>VirtualizedList</code> can't render your items fast enough, you may enter a part of your list with non-rendered components that appear as blank space.</p></li><li><p><strong>Viewport:</strong> The visible area of content that is rendered to pixels.</p></li><li><p><strong>Window:</strong> The area in which items should be mounted, which is generally much larger than the viewport.</p></li></ul><h2><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="props"></a>Props<a aria-hidden="true" tabindex="-1" class="hash-link" href="#props" title="Direct link to heading">#</a></h2><p>Here are a list of props that can help to improve <code>FlatList</code> performance:</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="removeclippedsubviews"></a>removeClippedSubviews<a aria-hidden="true" tabindex="-1" class="hash-link" href="#removeclippedsubviews" title="Direct link to heading">#</a></h3><table><thead><tr><th>Type</th><th>Default</th></tr></thead><tbody><tr><td>Boolean</td><td>False</td></tr></tbody></table><p>If <code>true</code>, views that are outside of the viewport are detached from the native view hierarchy.</p><p><strong>Pros:</strong> This reduces time spent on the main thread, and thus reduces the risk of dropped frames, by excluding views outside of the viewport from the native rendering and drawing traversals.</p><p><strong>Cons:</strong> Be aware that this implementation can have bugs, such as missing content (mainly observed on iOS), especially if you are doing complex things with transforms and/or absolute positioning. Also note this does not save significant memory because the views are not deallocated, only detached.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="maxtorenderperbatch"></a>maxToRenderPerBatch<a aria-hidden="true" tabindex="-1" class="hash-link" href="#maxtorenderperbatch" title="Direct link to heading">#</a></h3><table><thead><tr><th>Type</th><th>Default</th></tr></thead><tbody><tr><td>Number</td><td>10</td></tr></tbody></table><p>It is a <code>VirtualizedList</code> prop that can be passed through <code>FlatList</code>. This controls the amount of items rendered per batch, which is the next chunk of items rendered on every scroll.</p><p><strong>Pros:</strong> Setting a bigger number means less visual blank areas when scrolling (increases the fill rate).</p><p><strong>Cons:</strong> More items per batch means longer periods of JavaScript execution potentially blocking other event processing, like presses, hurting responsiveness.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="updatecellsbatchingperiod"></a>updateCellsBatchingPeriod<a aria-hidden="true" tabindex="-1" class="hash-link" href="#updatecellsbatchingperiod" title="Direct link to heading">#</a></h3><table><thead><tr><th>Type</th><th>Default</th></tr></thead><tbody><tr><td>Number</td><td>50</td></tr></tbody></table><p>While <code>maxToRenderPerBatch</code> tells the amount of items rendered per batch, setting <code>updateCellsBatchingPeriod</code> tells your <code>VirtualizedList</code> the delay in milliseconds between batch renders (how frequently your component will be rendering the windowed items).</p><p><strong>Pros:</strong> Combining this prop with <code>maxToRenderPerBatch</code> gives you the power to, for example, render more items in a less frequent batch, or less items in a more frequent batch.</p><p><strong>Cons:</strong> Less frequent batches may cause blank areas, More frequent batches may cause responsiveness issues.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="initialnumtorender"></a>initialNumToRender<a aria-hidden="true" tabindex="-1" class="hash-link" href="#initialnumtorender" title="Direct link to heading">#</a></h3><table><thead><tr><th>Type</th><th>Default</th></tr></thead><tbody><tr><td>Number</td><td>10</td></tr></tbody></table><p>The initial amount of items to render.</p><p><strong>Pros:</strong> Define precise number of items that would cover the screen for every device. This can be a big performance boost for the initial render.</p><p><strong>Cons:</strong> Setting a low <code>initialNumToRender</code> may cause blank areas, especially if it's too small to cover the viewport on initial render.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="windowsize"></a>windowSize<a aria-hidden="true" tabindex="-1" class="hash-link" href="#windowsize" title="Direct link to heading">#</a></h3><table><thead><tr><th>Type</th><th>Default</th></tr></thead><tbody><tr><td>Number</td><td>21</td></tr></tbody></table><p>The number passed here is a measurement unit where 1 is equivalent to your viewport height. The default value is 21 (10 viewports above, 10 below, and one in between).</p><p><strong>Pros:</strong> Bigger <code>windowSize</code> will result in less chance of seeing blank space while scrolling. On the other hand, smaller <code>windowSize</code> will result in fewer items mounted simultaneously, saving memory.</p><p><strong>Cons:</strong> For a bigger <code>windowSize</code>, you will have more memory consumption. For a lower <code>windowSize</code>, you will have a bigger chance of seeing blank areas.</p><h2><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="list-items"></a>List items<a aria-hidden="true" tabindex="-1" class="hash-link" href="#list-items" title="Direct link to heading">#</a></h2><p>Below are some tips about list item components. They are the core of your list, so they need to be fast.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-basic-components"></a>Use basic components<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-basic-components" title="Direct link to heading">#</a></h3><p>The more complex your components are, the slower they will render. Try to avoid a lot of logic and nesting in your list items. If you are reusing this list item component a lot in your app, create a component only for your big lists and make them with as little logic and nesting as possible.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-light-components"></a>Use light components<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-light-components" title="Direct link to heading">#</a></h3><p>The heavier your components are, the slower they render. Avoid heavy images (use a cropped version or thumbnail for list items, as small as possible). Talk to your design team, use as little effects and interactions and information as possible in your list. Show them in your item's detail.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-shouldcomponentupdate"></a>Use shouldComponentUpdate<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-shouldcomponentupdate" title="Direct link to heading">#</a></h3><p>Implement update verification to your components. React's <code>PureComponent</code> implement a <a href="https://reactjs.org/docs/react-component.html#shouldcomponentupdate" target="_blank" rel="noopener noreferrer"><code>shouldComponentUpdate</code></a> with shallow comparison. This is expensive here because it need to check all your props. If you want a good bit-level performance, create the strictest rules for your list item components, checking only props that could potentially change. If your list is basic enough, you could even use</p><div class="mdxCodeBlock_xYIz"><div class="codeBlockContent_rlEb"><button tabindex="0" type="button" aria-label="Copy code to clipboard" class="copyButton_kOW4">Copy</button><div class="prism-code language-jsx codeBlock_1AP7"><div class="codeBlockLines_1boI" style="color:#FFFFFF;background:#282C34"><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token function" style="color:#79b6f2">shouldComponentUpdate</span><span class="token punctuation" style="color:#657b83">(</span><span class="token punctuation" style="color:#657b83">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#657b83">{</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"> </span><span class="token keyword" style="color:#c5a5c5">return</span><span class="token plain"> </span><span class="token boolean" style="color:#ff8b50">false</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"></span><span class="token punctuation" style="color:#657b83">}</span></div></div></div></div></div><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-cached-optimized-images"></a>Use cached optimized images<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-cached-optimized-images" title="Direct link to heading">#</a></h3><p>You can use the community packages (such as <a href="https://github.com/DylanVann/react-native-fast-image" target="_blank" rel="noopener noreferrer">react-native-fast-image</a> from <a href="https://github.com/DylanVann" target="_blank" rel="noopener noreferrer">@DylanVann</a>) for more performant images. Every image in your list is a <code>new Image()</code> instance. The faster it reaches the <code>loaded</code> hook, the faster your JavaScript thread will be free again.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-getitemlayout"></a>Use getItemLayout<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-getitemlayout" title="Direct link to heading">#</a></h3><p>If all your list item components have the same height (or width, for a horizontal list), providing the <a href="/docs/flatlist#getitemlayout">getItemLayout</a> prop removes the need for your <code>FlatList</code> to manage async layout calculations. This is a very desirable optimization technique.</p><p>If your components have dynamic size and you really need performance, consider asking your design team if they may think of a redesign in order to perform better.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="use-keyextractor-or-key"></a>Use keyExtractor or key<a aria-hidden="true" tabindex="-1" class="hash-link" href="#use-keyextractor-or-key" title="Direct link to heading">#</a></h3><p>You can set the <a href="/docs/flatlist#keyextractor"><code>keyExtractor</code></a> to your <code>FlatList</code> component. This prop is used for caching and as the React <code>key</code> to track item re-ordering.</p><p>You can also use a <code>key</code> prop in you item component.</p><h3><a aria-hidden="true" tabindex="-1" class="anchor enhancedAnchor_3pqN" id="avoid-anonymous-function-on-renderitem"></a>Avoid anonymous function on renderItem<a aria-hidden="true" tabindex="-1" class="hash-link" href="#avoid-anonymous-function-on-renderitem" title="Direct link to heading">#</a></h3><p>Move out the <code>renderItem</code> function to the outside of render function, so it won't recreate itself each time render function called.</p><div class="mdxCodeBlock_xYIz"><div class="codeBlockContent_rlEb"><button tabindex="0" type="button" aria-label="Copy code to clipboard" class="copyButton_kOW4">Copy</button><div class="prism-code language-jsx codeBlock_1AP7"><div class="codeBlockLines_1boI" style="color:#FFFFFF;background:#282C34"><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token function-variable function" style="color:#79b6f2">renderItem</span><span class="token plain"> </span><span class="token operator" style="color:#fc929e">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#657b83">(</span><span class="token parameter punctuation" style="color:#657b83">{</span><span class="token parameter"> item </span><span class="token parameter punctuation" style="color:#657b83">}</span><span class="token punctuation" style="color:#657b83">)</span><span class="token plain"> </span><span class="token operator" style="color:#fc929e">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#657b83">(</span><span class="token tag punctuation" style="color:#657b83"><</span><span class="token tag class-name" style="color:#fac863">View</span><span class="token tag" style="color:#fc929e"> </span><span class="token tag attr-name" style="color:#c5a5c5">key</span><span class="token tag script language-javascript script-punctuation punctuation" style="color:#657b83">=</span><span class="token tag script language-javascript punctuation" style="color:#657b83">{</span><span class="token tag script language-javascript" style="color:#fc929e">item</span><span class="token tag script language-javascript punctuation" style="color:#657b83">.</span><span class="token tag script language-javascript" style="color:#fc929e">key</span><span class="token tag script language-javascript punctuation" style="color:#657b83">}</span><span class="token tag punctuation" style="color:#657b83">></span><span class="token tag punctuation" style="color:#657b83"><</span><span class="token tag class-name" style="color:#fac863">Text</span><span class="token tag punctuation" style="color:#657b83">></span><span class="token punctuation" style="color:#657b83">{</span><span class="token plain">item</span><span class="token punctuation" style="color:#657b83">.</span><span class="token plain">title</span><span class="token punctuation" style="color:#657b83">}</span><span class="token tag punctuation" style="color:#657b83"></</span><span class="token tag class-name" style="color:#fac863">Text</span><span class="token tag punctuation" style="color:#657b83">></span><span class="token tag punctuation" style="color:#657b83"></</span><span class="token tag class-name" style="color:#fac863">View</span><span class="token tag punctuation" style="color:#657b83">></span><span class="token punctuation" style="color:#657b83">)</span><span class="token punctuation" style="color:#657b83">;</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain" style="display:inline-block">
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</span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"></span><span class="token function" style="color:#79b6f2">render</span><span class="token punctuation" style="color:#657b83">(</span><span class="token punctuation" style="color:#657b83">)</span><span class="token punctuation" style="color:#657b83">{</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"> </span><span class="token comment" style="color:#93a1a1">// ...</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain" style="display:inline-block">
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</span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"> </span><span class="token tag punctuation" style="color:#657b83"><</span><span class="token tag class-name" style="color:#fac863">FlatList</span><span class="token tag" style="color:#fc929e"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token tag" style="color:#fc929e"> </span><span class="token tag attr-name" style="color:#c5a5c5">data</span><span class="token tag script language-javascript script-punctuation punctuation" style="color:#657b83">=</span><span class="token tag script language-javascript punctuation" style="color:#657b83">{</span><span class="token tag script language-javascript" style="color:#fc929e">items</span><span class="token tag script language-javascript punctuation" style="color:#657b83">}</span><span class="token tag" style="color:#fc929e"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token tag" style="color:#fc929e"> </span><span class="token tag attr-name" style="color:#c5a5c5">renderItem</span><span class="token tag script language-javascript script-punctuation punctuation" style="color:#657b83">=</span><span class="token tag script language-javascript punctuation" style="color:#657b83">{</span><span class="token tag script language-javascript" style="color:#fc929e">renderItem</span><span class="token tag script language-javascript punctuation" style="color:#657b83">}</span><span class="token tag" style="color:#fc929e"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token tag" style="color:#fc929e"> </span><span class="token tag punctuation" style="color:#657b83">/></span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain" style="display:inline-block">
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</span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"> </span><span class="token comment" style="color:#93a1a1">// ...</span><span class="token plain"></span></div><div class="token-line" style="color:#FFFFFF;background:#282C34"><span class="token plain"></span><span class="token punctuation" style="color:#657b83">}</span></div></div></div></div></div></div></article><div class="docMetadata margin-vert--xl"><div class="row"><div class="col"><a href="https://github.com/facebook/react-native-website/blob/master/website/versioned_docs/version-0.63/optimizing-flatlist-configuration.md" target="_blank" rel="noreferrer noopener"><svg fill="currentColor" height="1.2em" width="1.2em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 40 40" style="margin-right:0.3em;vertical-align:sub"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col text--right"><em><small class="docMetadata-updated">Last updated on <time datetime="2020-12-03T18:19:36.000Z" class="docLastUpdatedAt_1gIo">12/3/2020</time></small></em></div></div></div><div class="margin-vert--lg"><nav class="pagination-nav" aria-label="Blog list page navigation"><div class="pagination-nav__item"><a class="pagination-nav__link" href="/docs/performance"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">« Performance Overview</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/docs/ram-bundles-inline-requires"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">RAM Bundles and Inline Requires »</div></a></div></nav></div></div></div><div class="col col--3"><div class="tableOfContents_3iuQ"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#terms" class="table-of-contents__link">Terms</a></li><li><a href="#props" class="table-of-contents__link">Props</a><ul><li><a href="#removeclippedsubviews" class="table-of-contents__link">removeClippedSubviews</a></li><li><a href="#maxtorenderperbatch" class="table-of-contents__link">maxToRenderPerBatch</a></li><li><a href="#updatecellsbatchingperiod" class="table-of-contents__link">updateCellsBatchingPeriod</a></li><li><a href="#initialnumtorender" class="table-of-contents__link">initialNumToRender</a></li><li><a href="#windowsize" class="table-of-contents__link">windowSize</a></li></ul></li><li><a href="#list-items" class="table-of-contents__link">List items</a><ul><li><a href="#use-basic-components" class="table-of-contents__link">Use basic components</a></li><li><a href="#use-light-components" class="table-of-contents__link">Use light components</a></li><li><a href="#use-shouldcomponentupdate" class="table-of-contents__link">Use shouldComponentUpdate</a></li><li><a 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