Facebook/react-native
1
0
Fork 0
mirror of https://github.com/facebook/react-native.git synced 2025-11-01 09:14:26 +00:00
Code Issues Packages Projects Releases Wiki Activity
Files
dd009a401e1c6447a42ab84bbaf7c554da11f2de
react-native/docs/pixelratio.html
T
Website Deployment Script b7c2cdaf52 Deploy website 
Deploy website version based on 068c01bff8
2017-12-07 18:28:46 +00:00

126 lines
32 KiB
HTML
Raw Blame History

This file contains ambiguous Unicode characters
This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
<html><head><meta charset="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge, chrome=1"/><title>PixelRatio · React Native</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta property="og:title" content="PixelRatio · React Native"/><meta property="og:type" content="website"/><meta property="og:url" content="https://facebook.github.io/react-native/index.html"/><meta property="og:description" content="PixelRatio class gives access to the device pixel density."/><link rel="shortcut icon" href="/react-native/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/solarized-dark.min.css"/><link rel="alternate" type="application/atom+xml" href="https://facebook.github.io/blog/atom.xml" title="React Native Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://facebook.github.io/blog/feed.xml" title="React Native Blog RSS Feed"/><script type="text/javascript" src="https://snack.expo.io/embed.js"></script><script type="text/javascript" src="/react-native/js/codeblocks.js"></script><link rel="stylesheet" href="/react-native/css/main.css"/></head><body class="sideNavVisible"><div class="fixedHeaderContainer"><div class="headerWrapper wrapper"><header><a href="/react-native/"><img class="logo" src="/react-native/img/header_logo.png"/><h2 class="headerTitle">React Native</h2></a><a href="/react-native/versions.html"><h3>0.51</h3></a><div class="navigationWrapper navigationSlider"><nav class="slidingNav"><ul class="nav-site nav-site-internal"><li><a href="/react-native/docs/getting-started.html" target="_self">Docs</a></li><li><a href="/react-native/en/help.html" target="_self">Community</a></li><li><a href="/react-native/blog" target="_self">Blog</a></li><li class="navSearchWrapper reactNavSearchWrapper"><input type="text" id="search_input_react" placeholder="Search"/></li><li><a href="https://github.com/facebook/react-native" target="_self">GitHub</a></li><li><a href="https://reactjs.org/" target="_self">React</a></li></ul></nav></div></header></div></div><div class="navPusher"><div class="docMainWrapper wrapper"><div class="container docsNavContainer" id="docsNav"><nav class="toc"><div class="toggleNav"><section class="navWrapper wrapper"><div class="navBreadcrumb wrapper"><div class="navToggle" id="navToggler"><i></i></div><h2><i>›</i><span>APIs</span></h2></div><div class="navGroups"><div class="navGroup navGroupActive"><h3>The Basics</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/getting-started.html">Getting Started</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/tutorial.html">Learn the Basics</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/props.html">Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/state.html">State</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/style.html">Style</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/height-and-width.html">Height and Width</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/flexbox.html">Layout with Flexbox</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/handling-text-input.html">Handling Text Input</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/handling-touches.html">Handling Touches</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/using-a-scrollview.html">Using a ScrollView</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/using-a-listview.html">Using List Views</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/network.html">Networking</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/more-resources.html">More Resources</a></li></ul></div><div class="navGroup navGroupActive"><h3>Guides</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/components-and-apis.html">Components and APIs</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/platform-specific-code.html">Platform Specific Code</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/navigation.html">Navigating Between Screens</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/images.html">Images</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/animations.html">Animations</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/accessibility.html">Accessibility</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/improvingux.html">Improving User Experience</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/timers.html">Timers</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/debugging.html">Debugging</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/performance.html">Performance</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/gesture-responder-system.html">Gesture Responder System</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/javascript-environment.html">JavaScript Environment</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/direct-manipulation.html">Direct Manipulation</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/colors.html">Color Reference</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/integration-with-existing-apps.html">Integration with Existing Apps</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/running-on-device.html">Running On Device</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/upgrading.html">Upgrading to new React Native versions</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/troubleshooting.html">Troubleshooting</a></li></ul></div><div class="navGroup navGroupActive"><h3>Guides (iOS)</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/native-modules-ios.html">Native Modules</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/native-components-ios.html">Native UI Components</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/linking-libraries-ios.html">Linking Libraries</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/running-on-simulator-ios.html">Running On Simulator</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/communication-ios.html">Communication between native and React Native</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/building-for-apple-tv.html">Building For Apple TV</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/app-extensions.html">App Extensions</a></li></ul></div><div class="navGroup navGroupActive"><h3>Guides (Android)</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/native-modules-android.html">Native Modules</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/native-components-android.html">Native UI Components</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/headless-js-android.html">Headless JS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/signed-apk-android.html">Generating Signed APK</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/android-building-from-source.html">Building React Native from source</a></li></ul></div><div class="navGroup navGroupActive"><h3>Contributing</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/contributing.html">How to Contribute</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/maintainers.html">What to Expect from Maintainers</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/testing.html">Testing your Changes</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/understanding-cli.html">Understanding the CLI</a></li></ul></div><div class="navGroup navGroupActive"><h3>Components</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/activityindicator.html">ActivityIndicator</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/button.html">Button</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/datepickerios.html">DatePickerIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/drawerlayoutandroid.html">DrawerLayoutAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/flatlist.html">FlatList</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/image.html">Image</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/keyboardavoidingview.html">KeyboardAvoidingView</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/listview.html">ListView</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/maskedviewios.html">MaskedViewIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/modal.html">Modal</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/navigatorios.html">NavigatorIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/picker.html">Picker</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/pickerios.html">PickerIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/progressbarandroid.html">ProgressBarAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/progressviewios.html">ProgressViewIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/refreshcontrol.html">RefreshControl</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/scrollview.html">ScrollView</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/sectionlist.html">SectionList</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/segmentedcontrolios.html">SegmentedControlIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/slider.html">Slider</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/snapshotviewios.html">SnapshotViewIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/statusbar.html">StatusBar</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/switch.html">Switch</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/tabbarios.html">TabBarIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/tabbarios-item.html">TabBarIOS.Item</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/text.html">Text</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/textinput.html">TextInput</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/toolbarandroid.html">ToolbarAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/touchablehighlight.html">TouchableHighlight</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/touchablenativefeedback.html">TouchableNativeFeedback</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/touchableopacity.html">TouchableOpacity</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/touchablewithoutfeedback.html">TouchableWithoutFeedback</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/view.html">View</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/viewpagerandroid.html">ViewPagerAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/virtualizedlist.html">VirtualizedList</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/webview.html">WebView</a></li></ul></div><div class="navGroup navGroupActive"><h3>APIs</h3><ul><li class="navListItem"><a class="navItem" href="/react-native/docs/accessibilityinfo.html">AccessibilityInfo</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/actionsheetios.html">ActionSheetIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/alert.html">Alert</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/alertios.html">AlertIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/animated.html">Animated</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/appregistry.html">AppRegistry</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/appstate.html">AppState</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/asyncstorage.html">AsyncStorage</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/backandroid.html">BackAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/backhandler.html">BackHandler</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/cameraroll.html">CameraRoll</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/clipboard.html">Clipboard</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/datepickerandroid.html">DatePickerAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/dimensions.html">Dimensions</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/easing.html">Easing</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/geolocation.html">Geolocation</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/imageeditor.html">ImageEditor</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/imagepickerios.html">ImagePickerIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/imagestore.html">ImageStore</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/image-style-props.html">Image Style Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/interactionmanager.html">InteractionManager</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/keyboard.html">Keyboard</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/layout-props.html">Layout Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/layoutanimation.html">LayoutAnimation</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/linking.html">Linking</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/listviewdatasource.html">ListViewDataSource</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/netinfo.html">NetInfo</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/panresponder.html">PanResponder</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/permissionsandroid.html">PermissionsAndroid</a></li><li class="navListItem navListItemActive"><a class="navItem navItemActive" href="/react-native/docs/pixelratio.html">PixelRatio</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/pushnotificationios.html">PushNotificationIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/settings.html">Settings</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/shadow-props.html">Shadow Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/share.html">Share</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/statusbarios.html">StatusBarIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/stylesheet.html">StyleSheet</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/systrace.html">Systrace</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/text-style-props.html">Text Style Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/timepickerandroid.html">TimePickerAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/toastandroid.html">ToastAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/transforms.html">Transforms</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/vibration.html">Vibration</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/vibrationios.html">VibrationIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/view-style-props.html">View Style Props</a></li></ul></div></div></section></div><script>
var toggler = document.getElementById('navToggler');
var nav = document.getElementById('docsNav');
toggler.onclick = function() {
nav.classList.toggle('docsSliderActive');
};
</script></nav></div><div class="container mainContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/facebook/react-native-website/blob/master/docs/pixelratio.md" target="_blank">Edit</a><h1>PixelRatio</h1></header><article><div><span><p>PixelRatio class gives access to the device pixel density.</p>
<h2><a class="anchor" aria-hidden="true" name="fetching-a-correctly-sized-image"></a><a href="#fetching-a-correctly-sized-image" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Fetching a correctly sized image</h2>
<p>You should get a higher resolution image if you are on a high pixel density
device. A good rule of thumb is to multiply the size of the image you display
by the pixel ratio.</p>
<pre><code class="hljs"><span class="hljs-built_in">var</span> <span class="hljs-built_in">image</span> = getImage({
<span class="hljs-built_in">width</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">200</span>),
<span class="hljs-built_in">height</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">100</span>),
});
&lt;Image source={<span class="hljs-built_in">image</span>} <span class="hljs-built_in">style</span>={{<span class="hljs-built_in">width</span>: <span class="hljs-number">200</span>, <span class="hljs-built_in">height</span>: <span class="hljs-number">100</span>}} /&gt;
</code></pre>
<h2><a class="anchor" aria-hidden="true" name="pixel-grid-snapping"></a><a href="#pixel-grid-snapping" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Pixel grid snapping</h2>
<p>In iOS, you can specify positions and dimensions for elements with arbitrary
precision, for example 29.674825. But, ultimately the physical display only
have a fixed number of pixels, for example 640×960 for iPhone 4 or 750×1334
for iPhone 6. iOS tries to be as faithful as possible to the user value by
spreading one original pixel into multiple ones to trick the eye. The
downside of this technique is that it makes the resulting element look
blurry.</p>
<p>In practice, we found out that developers do not want this feature and they
have to work around it by doing manual rounding in order to avoid having
blurry elements. In React Native, we are rounding all the pixels
automatically.</p>
<p>We have to be careful when to do this rounding. You never want to work with
rounded and unrounded values at the same time as you're going to accumulate
rounding errors. Having even one rounding error is deadly because a one
pixel border may vanish or be twice as big.</p>
<p>In React Native, everything in JavaScript and within the layout engine works
with arbitrary precision numbers. It's only when we set the position and
dimensions of the native element on the main thread that we round. Also,
rounding is done relative to the root rather than the parent, again to avoid
accumulating rounding errors.</p>
<h3><a class="anchor" aria-hidden="true" name="methods"></a><a href="#methods" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Methods</h3>
<ul>
<li><a href="/react-native/docs/pixelratio.html#get"><code>get</code></a></li>
<li><a href="/react-native/docs/pixelratio.html#getfontscale"><code>getFontScale</code></a></li>
<li><a href="/react-native/docs/pixelratio.html#getpixelsizeforlayoutsize"><code>getPixelSizeForLayoutSize</code></a></li>
<li><a href="/react-native/docs/pixelratio.html#roundtonearestpixel"><code>roundToNearestPixel</code></a></li>
<li><a href="/react-native/docs/pixelratio.html#startdetecting"><code>startDetecting</code></a></li>
</ul>
<hr>
<h1><a class="anchor" aria-hidden="true" name="reference"></a><a href="#reference" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Reference</h1>
<h2><a class="anchor" aria-hidden="true" name="methods"></a><a href="#methods" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Methods</h2>
<h3><a class="anchor" aria-hidden="true" name="get"></a><a href="#get" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>get()</code></h3>
<pre><code class="hljs css javascript"><span class="hljs-keyword">static</span> get()
</code></pre>
<p>Returns the device pixel density. Some examples:</p>
<ul>
<li>PixelRatio.get() === 1
<ul>
<li>mdpi Android devices (160 dpi)</li>
</ul></li>
<li>PixelRatio.get() === 1.5
<ul>
<li>hdpi Android devices (240 dpi)</li>
</ul></li>
<li>PixelRatio.get() === 2
<ul>
<li>iPhone 4, 4S</li>
<li>iPhone 5, 5c, 5s</li>
<li>iPhone 6</li>
<li>xhdpi Android devices (320 dpi)</li>
</ul></li>
<li>PixelRatio.get() === 3
<ul>
<li>iPhone 6 plus</li>
<li>xxhdpi Android devices (480 dpi)</li>
</ul></li>
<li>PixelRatio.get() === 3.5
<ul>
<li>Nexus 6</li>
</ul></li>
</ul>
<hr>
<h3><a class="anchor" aria-hidden="true" name="getfontscale"></a><a href="#getfontscale" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getFontScale()</code></h3>
<pre><code class="hljs css javascript"><span class="hljs-keyword">static</span> getFontScale()
</code></pre>
<p>Returns the scaling factor for font sizes. This is the ratio that is used to calculate the
absolute font size, so any elements that heavily depend on that should use this to do
calculations.</p>
<p>If a font scale is not set, this returns the device pixel ratio.</p>
<p>Currently this is only implemented on Android and reflects the user preference set in
Settings &gt; Display &gt; Font size, on iOS it will always return the default pixel ratio.
@platform android</p>
<hr>
<h3><a class="anchor" aria-hidden="true" name="getpixelsizeforlayoutsize"></a><a href="#getpixelsizeforlayoutsize" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getPixelSizeForLayoutSize()</code></h3>
<pre><code class="hljs css javascript"><span class="hljs-keyword">static</span> getPixelSizeForLayoutSize(layoutSize)
</code></pre>
<p>Converts a layout size (dp) to pixel size (px).</p>
<p>Guaranteed to return an integer number.</p>
<hr>
<h3><a class="anchor" aria-hidden="true" name="roundtonearestpixel"></a><a href="#roundtonearestpixel" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>roundToNearestPixel()</code></h3>
<pre><code class="hljs css javascript"><span class="hljs-keyword">static</span> roundToNearestPixel(layoutSize)
</code></pre>
<p>Rounds a layout size (dp) to the nearest layout size that corresponds to
an integer number of pixels. For example, on a device with a PixelRatio
of 3, <code>PixelRatio.roundToNearestPixel(8.4) = 8.33</code>, which corresponds to
exactly (8.33 * 3) = 25 pixels.</p>
<hr>
<h3><a class="anchor" aria-hidden="true" name="startdetecting"></a><a href="#startdetecting" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>startDetecting()</code></h3>
<pre><code class="hljs css javascript"><span class="hljs-keyword">static</span> startDetecting()
</code></pre>
<p>// No-op for iOS, but used on the web. Should not be documented.</p>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="permissionsandroid.html">← PermissionsAndroid</a><a class="docs-next button" href="pushnotificationios.html">PushNotificationIOS →</a></div></div></div></div><footer class="nav-footer" id="footer"><section class="sitemap"><a href="/react-native/" class="nav-home"><img src="/react-native/img/header_logo.png" alt="React Native" width="66" height="58"/></a><div><h5><a href="/react-native/docs/getting-started.html">Docs</a></h5><a href="/react-native/docs/getting-started.html">Getting Started</a><a href="/react-native/docs/tutorial.html">Learn the Basics</a><a href="/react-native/docs/components-and-apis.html">Components and APIs</a><a href="/react-native/docs/more-resources.html">More Resources</a></div><div><h5><a href="/react-native/help.html">Community</a></h5><a href="/react-native/showcase.html">Who&#x27;s using React Native?</a><a href="http://www.meetup.com/topics/react-native/" target="_blank">Meetups</a><a href="https://www.facebook.com/groups/react.native.community" target="_blank">Facebook Group</a><a href="https://twitter.com/reactnative" target="_blank">Twitter</a></div><div><h5><a href="/react-native/help.html">Help</a></h5><a href="http://stackoverflow.com/questions/tagged/react-native" target="_blank">Stack Overflow</a><a href="https://discord.gg/0ZcbPKXt5bZjGY5n">Reactiflux Chat</a><a href="/react-native/versions.html" target="_blank">Latest Releases</a><a href="https://react-native.canny.io/feature-requests" target="_blank">Feature Requests</a></div><div><h5>More</h5><a href="/react-native/blog">Blog</a><a href="http://reactjs.org" target="_blank">React</a><a href="https://github.com/facebook/react-native" target="_blank">GitHub</a><div class="githubButton"><a class="github-button" href="https://github.com/facebook/react-native" data-icon="octicon-star" data-show-count="true" data-count-href="/facebook/react-native/stargazers" data-count-api="/repos/facebook/react-native#stargazers_count" data-count-aria-label="# stargazers on GitHub" aria-label="Star facebook/react-native on GitHub">Star</a></div></div></section><a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource"><img src="/react-native/img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"/></a><section class="copyright">Copyright © 2017 Facebook Inc.</section></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-41298772-2', 'auto');
ga('send', 'pageview');
</script><script>window.fbAsyncInit = function() {FB.init({appId:'1677033832619985',xfbml:true,version:'v2.7'});};(function(d, s, id){var js, fjs = d.getElementsByTagName(s)[0];if (d.getElementById(id)) {return;}js = d.createElement(s); js.id = id;js.src = '//connect.facebook.net/en_US/sdk.js';fjs.parentNode.insertBefore(js, fjs);}(document, 'script','facebook-jssdk'));
</script><script>window.twttr=(function(d,s, id){var js,fjs=d.getElementsByTagName(s)[0],t=window.twttr||{};if(d.getElementById(id))return t;js=d.createElement(s);js.id=id;js.src='https://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js, fjs);t._e = [];t.ready = function(f) {t._e.push(f);};return t;}(document, 'script', 'twitter-wjs'));</script><script>
var search = docsearch({
apiKey: '2c98749b4a1e588efec53b2acec13025',
indexName: 'react-native-versions',
inputSelector: '#search_input_react',
algoliaOptions: {"facetFilters":["tags:0.51"],"hitsPerPage":5}
});
</script></body></html>
Reference in New Issue View Git Blame Copy Permalink