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</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" rel="noreferrer noopener">Edit</a><h1 class="postHeaderTitle">PixelRatio</h1></header><article><div><span><p>PixelRatio class gives access to the device pixel density.</p>
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<p>There are a few use cases for using PixelRatio:</p>
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<h3><a class="anchor" aria-hidden="true" id="displaying-a-line-that-s-as-thin-as-the-device-permits"></a><a href="#displaying-a-line-that-s-as-thin-as-the-device-permits" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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>Displaying a line that's as thin as the device permits</h3>
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<p>A width of 1 is actually pretty thick on devices with high pixel density (such as iPhone 4+ and many Android devices), we can make one that's thinner using a width of <code>1 / PixelRatio.get()</code>. It's a technique that works on all the devices independent of their pixel density.</p>
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<pre><code class="hljs"><span class="hljs-attr">style</span>={{ borderWidth: <span class="hljs-number">1</span> / PixelRatio.get() }}
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</code></pre>
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<h3><a class="anchor" aria-hidden="true" id="fetching-a-correctly-sized-image"></a><a href="#fetching-a-correctly-sized-image" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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</h3>
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<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>
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<pre><code class="hljs"><span class="hljs-built_in">var</span> <span class="hljs-built_in">image</span> = getImage({
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<span class="hljs-built_in">width</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">200</span>),
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<span class="hljs-built_in">height</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">100</span>),
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});
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<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>}} />
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</code></pre>
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||
<h3><a class="anchor" aria-hidden="true" id="methods"></a><a href="#methods" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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>
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<ul>
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<li><a href="/react-native/docs/0.13/pixelratio#get"><code>get</code></a></li>
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<li><a href="/react-native/docs/0.13/pixelratio#getfontscale"><code>getFontScale</code></a></li>
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<li><a href="/react-native/docs/0.13/pixelratio#getpixelsizeforlayoutsize"><code>getPixelSizeForLayoutSize</code></a></li>
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<li><a href="/react-native/docs/0.13/pixelratio#startdetecting"><code>startDetecting</code></a></li>
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</ul>
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||
<hr>
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||
<h1><a class="anchor" aria-hidden="true" id="reference"></a><a href="#reference" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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" id="methods-1"></a><a href="#methods-1" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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" id="get"></a><a href="#get" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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 languages- 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><a href="https://material.io/tools/devices/">mdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 1.5
|
||
<ul>
|
||
<li><a href="https://material.io/tools/devices/">hdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 2
|
||
<ul>
|
||
<li>iPhone 4, 4S</li>
|
||
<li>iPhone 5, 5c, 5s</li>
|
||
<li>iPhone 6, 7, 8</li>
|
||
<li><a href="https://material.io/tools/devices/">xhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 3
|
||
<ul>
|
||
<li>iPhone 6 Plus, 7 Plus, 8 Plus</li>
|
||
<li>iPhone X</li>
|
||
<li>Pixel, Pixel 2</li>
|
||
<li><a href="https://material.io/tools/devices/">xxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 3.5
|
||
<ul>
|
||
<li>Nexus 6</li>
|
||
<li>Pixel XL, Pixel 2 XL</li>
|
||
<li><a href="https://material.io/tools/devices/">xxxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
</ul>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getfontscale"></a><a href="#getfontscale" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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 languages- 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 > Display > Font size, on iOS it will always return the default pixel ratio. @platform android</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getpixelsizeforlayoutsize"></a><a href="#getpixelsizeforlayoutsize" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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 languages- 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" id="startdetecting"></a><a href="#startdetecting" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" 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 languages- 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>
|
||
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