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		value: 维护兼容性
		- name: zh-tw-lang
		value: 維持相容性
		- title: Selecting Colors with the Palette API
		path: /training/material/palette-colors.html

		- title: Best Practices for User Input
		path: /training/best-user-input.html

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		page.image=images/cards/material_2x.png
		page.metaDescription=Learn how to apply material design to your apps.


		@jd:body

		<div id="tb-wrapper">
		@@ -58,6 +57,9 @@ specification</a> and use the new components and functionality available in Andr

		<dt><a href="{@docRoot}training/material/compatibility.html">Maintaining Compatibility</a></dt>
		<dd>Learn how to maintain compatibility with platform versions earlier than Android 5.0.</dd>

		<dt><a href="{@docRoot}training/material/palette-colors.html">Selecting Colors with the Palette API</a></dt>
		<dd>Learn how to select colors for your app using the v7 Palette library.</dd>
		</dl>

		<h2>Video Training</h2>

docs/html/training/material/palette-colors.html

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		<html devsite>
		<head>
		<title>Selecting Colors with the Palette API</title>
		<meta name="book_path" value="/training/_book.yaml" />
		<meta name="top_category" value="develop" />
		<meta name="subcategory" value="training" />
		</head>
		<body>

		<div id="tb-wrapper">
		<div id="tb">
		<h2>This lesson teaches you to</h2>
		<ol>
		<li><a href="#set-up-the-library">Set up the library</a></li>
		<li><a href="#create-a-palette">Create a palette</a>
		<ol>
		<li><a href="#generate-a-palette-instance">Generate a Palette instance</a></li>
		<li><a href="#customize-your-palette">Customize your palette</a></li>
		</ol>
		</li>
		<li><a href="#extract-color-profiles">Extract color profiles</a>
		<ol>
		<li><a href="#use-swatches">Use swatches to create color schemes</a></li>
		</ol>
		</li>
		</ol>
		<h2>You should also read</h2>
		<ul>
		<li><a href="http://www.google.com/design/spec">Material design specification</a></li>
		<li><a href="/design/material/index.html">Material design on Android</a></li>
		</ul>
		</div>
		</div>

		<p>Good visual design is essential for a successful app, and color schemes are a primary component of design. The palette library is a
		<a href="/topic/libraries/support-library/features.html#v7-palette">support library</a>
		that extracts prominent colors from images to help you create visually engaging apps.</p>

		<p>You can use the palette library to design layout
		<a href="/guide/topics/ui/themes.html">themes</a> and apply custom colors to visual elements in your app.
		For example, you can use a palette to create a color-coordinated title
		card for a song based on its album cover or to adjust an app’s toolbar color when its
		background image changes. The <code><a
		href="/reference/android/support/v7/graphics/Palette.html">Palette</a></code> object gives
		you access to the colors in a <code><a
		href="/reference/android/graphics/Bitmap.html">Bitmap</a></code>
		image while also providing six main color profiles from the bitmap to help
		inform your <a href="http://material.google.com">design choices</a>.</p>

		<h2 id="set-up-the-library">Set up the library</h2>

		<p>To use the palette library, install or update the <a
		href="/topic/libraries/support-library/index.html">Android
		Support Library</a> to version 24.0.0 or higher and follow the instructions for <a
		href="/topic/libraries/support-library/setup.html#add-library">Adding
		Support Libraries</a> to add the palette library to your app development project.</p>

		<p>Make sure that the version specified in your dependency identifier matches your
		app’s <code>compileSdkVersion</code>, set in the <code>build.gradle</code>
		file:</p>

		<pre class="prettyprint">
		android {
		compileSdkVersion 24
		...
		}

		dependencies {
		...
		compile 'com.android.support:palette-v7:24.2.1'
		}
		</pre>

		<p>For more information about adding the palette dependency, read about the palette
		feature in the <a
		href="/topic/libraries/support-library/features.html#v7-palette">support
		library documentation</a>.</p>

		<h2 id="create-a-palette">Create a palette</h2>

		<p>A <code>Palette</code> object gives you access to the primary colors in an
		image, as well as the corresponding colors for overlaid text. Use palettes to design
		your app’s style and to dynamically change your app’s color scheme based on a
		given source image.</p>

		<p>To create a palette, first instantiate a <code><a
		href="https://developer.android.com/reference/android/support/v7/graphics/Palette.Builder.html">Palette.Builder</a></code>
		from a <code>Bitmap</code>. You can then use the
		<code>Palette.Builder</code> to customize the palette before generating it. This
		section will describe palette generation and customization from a bitmap
		image.</p>

		<h3 id="generate-a-palette-instance">Generate a Palette instance</h3>

		<p>Generate a <code>Palette</code> instance using <code>Palette</code>’s
		<code><a
		href="/reference/android/support/v7/graphics/Palette.html#from(android.graphics.Bitmap)">from(Bitmap
		bitmap)</a></code> method to first create a <code>Palette.Builder</code>
		from a <code>Bitmap</code>. The builder can then generate the palette either
		synchronously or asynchronously.</p>

		<p>Use synchronous palette generation if you want to create the palette on
		the same thread as the method being called. If you generate the palette
		asynchronously on a different thread, use the <code><a
		href="/reference/android/support/v7/graphics/Palette.PaletteAsyncListener.html#onGenerated(android.support.v7.graphics.Palette)">onGenerated()</a></code>
		method to access the palette immediately after it has been created.</p>

		<p>The following code snippet provides example methods for both types of palette generation:</p>

		<pre class="prettyprint">
		// Generate palette synchronously and return it
		public Palette createPaletteSync(Bitmap bitmap) {
		Palette p = Palette.from(bitmap).generate();
		return p;
		}

		// Generate palette asynchronously and use it on a different
		// thread using onGenerated()
		public void createPaletteAsync(Bitmap bitmap) {
		Palette.from(bitmap).generate(new PaletteAsyncListener() {
		public void onGenerated(Palette p) {
		// Use generated instance
		}
		});
		}
		</pre>

		<p>If you need to continuously generate palettes for a sorted list of images
		or objects, consider <a
		href="/reference/android/util/LruCache.html">caching</a>
		the <code>Palette</code> instances to prevent slow UI performance. You also
		should not create the palettes on your <a href="/training/articles/perf-anr.html">main thread</a>.</p>

		<h3 id="customize-your-palette">Customize your palette</h3>

		<p>The <code>Palette.Builder</code> allows you to customize your palette by
		choosing how many colors are in the resulting palette, what area of your
		image the builder uses to generate the palette, and what colors are allowed in the
		palette. For example, you can filter out the color black or ensure that the
		builder only uses the top half of an image to generate your palette.</p>

		<p>Fine-tune your palette’s size and colors with the following methods from
		the <code>Palette.Builder</code> class:</p>

		<dl>

		<dt><code><a
		href="/reference/android/support/v7/graphics/Palette.Builder.html#addFilter(android.support.v7.graphics.Palette.Filter)">addFilter()</a></code></dt>
		<dd>This method adds a filter that indicates what colors are allowed in the
		resulting palette. Pass in your own<code> <a
		href="/reference/android/support/v7/graphics/Palette.Filter.html">Palette.Filter</a></code>
		and modify its <code>isAllowed()</code> method to determine which colors are
		filtered from the palette.</dd>

		<dt><code><a
		href="/reference/android/support/v7/graphics/Palette.Builder.html#maximumColorCount(int)">maximumColorCount()</a></code></dt>
		<dd>This method sets the maximum number of colors in your palette. The
		default value is 16, and the optimal value depends on the source image.
		For landscapes, optimal values range from 8-16 while pictures with faces
		usually have values that fall between 24-32. The
		<code>Palette.Builder</code> takes longer to generate palettes with more
		colors.</dd>

		<dt><code><a
		href="/reference/android/support/v7/graphics/Palette.Builder.html#setRegion(int,%20int,%20int,%20int)">setRegion()</a></code></dt>
		<dd>This method indicates what area of the bitmap the builder uses when
		creating the palette. You can only use this method when generating the palette from
		a bitmap, and it does not affect the original image.</dd>

		<dt><code><a
		href="/reference/android/support/v7/graphics/Palette.Builder.html#addTarget(android.support.v7.graphics.Target)">addTarget()</a></code></dt>
		<dd>This method allows you to perform your own color matching by adding a
		<code><a
		href="/reference/android/support/v7/graphics/Target.html">Target</a></code>
		color profile to the builder. If the default <code>Target</code>s are not
		sufficient, advanced developers can create their own <code>Target</code>s
		using a <code><a
		href="/reference/android/support/v7/graphics/Target.Builder.html">Target.Builder</a></code>.</dd>

		</dl>

		<h2 id="extract-color-profiles">Extract color profiles</h2>

		<p>Based on the <a
		href="https://material.google.com/style/color.html#">standards
		of material design</a>, the palette library extracts commonly used color
		profiles from an image. Each profile is defined by a <code><a
		href="/reference/android/support/v7/graphics/Target.html">Target</a></code>,
		and colors extracted from the bitmap image are scored against each profile
		based on saturation, luminance, and population (number of pixels in the bitmap
		represented by the color). For each profile, the color with the best score
		defines that color profile for the given image.</p>

		<p>By default, a <code>Palette</code> object contains 16 primary colors from
		a given image. When generating your palette, you can <a
		href="#customize-your-palette">customize</a> its number of colors using the
		<code>Palette.Builder</code>. Extracting more colors provides more potential
		matches for each color profile but also causes <code>Palette.Builder</code> to
		take longer when generating the palette.</p>

		<p>The palette library attempts to extract the following six color
		profiles:</p>

		<ul>
		<li>Light Vibrant</li>
		<li>Vibrant</li>
		<li>Dark Vibrant</li>
		<li>Light Muted</li>
		<li>Muted</li>
		<li>Dark Muted</li>
		</ul>

		<p>Each of <code>Palette</code>’s <code>get<<em>Profile</em>>Color()</code>
		methods returns the color in the palette associated with that particular profile,
		where <code><<em>Profile</em>></code> is replaced by the name of one of the six
		color profiles. For example, the method to get the Dark Vibrant color profile is <code><a
		href="/reference/android/support/v7/graphics/Palette.html#getDarkVibrantColor(int)">getDarkVibrantColor()</a></code>.
		Since not all images will contain all color profiles, you must also provide
		a default color to return.</p>

		<p>Figure 1 displays a photo and its corresponding color
		profiles from the <code>get<<em>Profile</em>>Color()</code> methods.</p>

		<img src="/training/material/images/palette-library-color-profiles_2-1_2x.png" alt="" width="624"/>

		<p class="img-caption"><strong>Figure 1.</strong> An example image and its
		extracted color profiles given the default maximum color count (16) for the palette.</p>

		<h3 id="use-swatches">Use swatches to create color schemes</h3>

		<p>The <code>Palette</code> class also generates <code><a
		href="/reference/android/support/v7/graphics/Palette.Swatch.html">Palette.Swatch</a></code>
		objects for each color profile. <code>Palette.Swatch</code>
		objects contain the associated color for that profile, as well as the
		color’s population in pixels.</p>

		<p>Swatches have additional methods for accessing more information about the color
		profile, such as HSL values and pixel population. You can use swatches to help
		create more comprehensive color schemes and app themes using the <code><a
		href="/reference/android/support/v7/graphics/Palette.Swatch.html#getBodyTextColor()">getBodyTextColor()</a></code>
		and <code><a
		href="/reference/android/support/v7/graphics/Palette.Swatch.html#getTitleTextColor()">getTitleTextColor()</a></code>
		methods. These methods return colors appropriate for use over the swatch’s
		color.</p>

		<p>Each of <code>Palette</code>’s <code>get<<em>Profile</em>>Swatch()</code>
		methods returns the swatch associated with that particular profile,
		where <code><<em>Profile</em>></code> is replaced by the name of one of the six
		color profiles. Although the palette’s <code>get<<em>Profile</em>>Swatch()</code> methods
		do not require default value parameters, they return <code>null</code> if that
		particular profile does not exist in the image. Therefore, you should check that
		a swatch is not null before using it. For example, the following method
		returns the Vibrant swatch from a palette if the swatch is not null:</p>

		<pre class="prettyprint">
		// Return a palette's vibrant swatch after checking that it exists
		private Palette.Swatch checkVibrantSwatch(Palette p) {
		Palette.Swatch vibrant = p.getVibrantSwatch();
		if (vibrant != null) {
		return vibrant;
		}
		// Throw error
		}
		</pre>

		<p>To access all colors in a palette, the <code><a
		href="/reference/android/support/v7/graphics/Palette.html#getSwatches()">getSwatches()</a></code>
		method returns a list of all swatches generated from an
		image, including the standard six color profiles.</p>

		<p>The following snippet of code uses the methods from the above code snippets to
		synchronously generate a palette, get its vibrant swatch, and change the colors of a
		toolbar to match the bitmap image. Figure 2 displays the resulting image and toolbar.</p>

		<div class="cols">

		<div class="col-2of3">

		<pre class="prettyprint">
		// Set the background and text colors of a toolbar given a
		// bitmap image to match
		public void setToolbarColor(Bitmap bitmap) {
		// Generate the palette and get the vibrant swatch
		// See the createPaletteSync() and checkVibrantSwatch() methods
		// from the code snippets above
		Palette p = createPaletteSync(bitmap);
		Palette.Swatch vibrantSwatch = checkVibrantSwatch(p);

		// Set the toolbar background and text colors
		Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
		toolbar.setBackgroundColor(vibrantSwatch.getRgb());
		toolbar.setTitleTextColor(vibrantSwatch.getTitleTextColor());
		}
		</pre>

		</div>

		<div class="col-1of3">

		<img src="/training/material/images/palette-library-title-text-color_2-1_2x.png" alt="" width="400"/>

		<p class="img-caption"><strong>Figure 2.</strong> An example image with its
		vibrant-colored toolbar and corresponding title text color.</p>

		</div>

		</div>

		</body>
		</html>