651 lines
25 KiB
HTML
651 lines
25 KiB
HTML
<html>
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<head>
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<script type="text/javascript" src="http://www.corp.google.com/style/prettify.js"></script>
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<script src="http://www.corp.google.com/eng/techpubs/include/navbar.js" type="text/javascript"></script>
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</head>
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<body>
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<p>Contains classes for accessing and publishing data
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on the device. It includes three main categories of APIs:
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the {@link android.content.res.Resources Resources} for
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retrieving resource data associated with an application;
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{@link android.content.ContentProvider Content Providers} and
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{@link android.content.ContentResolver ContentResolver} for managing and
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publishing persistent data associated with an application; and
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the {@link android.content.pm.PackageManager Package Manager}
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for finding out information about the application packages installed
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on the device.</p>
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<p>In addition, the {@link android.content.Context Context} abstract class
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is a base API for pulling these pieces together, allowing you to access
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an application's resources and transfer data between applications.</p>
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<p>This package builds on top of the lower-level Android packages
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{@link android.database}, {@link android.text},
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{@link android.graphics.drawable}, {@link android.graphics},
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{@link android.os}, and {@link android.util}.</p>
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<ol>
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<li> <a href="#Resources">Resources</a>
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<ol>
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<li> <a href="#ResourcesTerminology">Terminology</a>
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<li> <a href="#ResourcesQuickStart">Examples</a>
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<ol>
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<li> <a href="#UsingSystemResources">Using System Resources</a>
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<li> <a href="#StringResources">String Resources</a>
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<li> <a href="#ColorResources">Color Resources</a>
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<li> <a href="#DrawableResources">Drawable Resources</a>
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<li> <a href="#LayoutResources">Layout Resources</a>
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<li> <a href="#ReferencesToResources">References to Resources</a>
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<li> <a href="#ReferencesToThemeAttributes">References to Theme Attributes</a>
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<li> <a href="#StyleResources">Style Resources</a>
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<li> <a href="#StylesInLayoutResources">Styles in Layout Resources</a>
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</ol>
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</ol>
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</ol>
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<a name="Resources"></a>
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<h2>Resources</h2>
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<p>This topic includes a terminology list associated with resources, and a series
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of examples of using resources in code. For a complete guide on creating and
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using resources, see the document on <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources
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and Internationalization</a>. For a reference on the supported Android resource types,
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see <a href="{@docRoot}guide/topics/resources/available-resources.html">Available Resource Types</a>.</p>
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<p>The Android resource system keeps track of all non-code
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assets associated with an application. You use the
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{@link android.content.res.Resources Resources} class to access your
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application's resources; the Resources instance associated with your
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application can generally be found through
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{@link android.content.Context#getResources Context.getResources()}.</p>
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<p>An application's resources are compiled into the application
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binary at build time for you by the build system. To use a resource,
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you must install it correctly in the source tree and build your
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application. As part of the build process, Java symbols for each
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of the resources are generated that you can use in your source
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code -- this allows the compiler to verify that your application code matches
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up with the resources you defined.</p>
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<p>The rest of this section is organized as a tutorial on how to
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use resources in an application.</p>
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<a name="ResourcesTerminology"></a>
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<h3>Terminology</h3>
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<p>The resource system brings a number of different pieces together to
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form the final complete resource functionality. To help understand the
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overall system, here are some brief definitions of the core concepts and
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components you will encounter in using it:</p>
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<p><b>Asset</b>: A single blob of data associated with an application. This
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includes Java object files, graphics (such as PNG images), XML files, etc.
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These files are organized in a directory hierarchy that, during final packaging
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of the application, is bundled together into a single ZIP file.</p>
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<p><b>aapt</b>: The tool that generates the final ZIP file of application
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assets. In addition to collecting raw assets together, it also parses
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resource definitions into binary asset data.</p>
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<p><b>Resource Table</b>: A special asset that aapt generates for you,
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describing all of the resources contained in an application/package.
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This file is accessed for you by the Resources class; it is not touched
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directly by applications.</p>
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<p><b>Resource</b>: An entry in the Resource Table describing a single
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named value. Broadly, there are two types of resources: primitives and
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bags.</p>
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<p><b>Resource Identifier</b>: In the Resource Table all resources are
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identified by a unique integer number. In source code (resource descriptions,
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XML files, Java code) you can use symbolic names that stand as constants for
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the actual resource identifier integer.</p>
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<p><b>Primitive Resource</b>: All primitive resources can be written as a
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simple string, using formatting to describe a variety of primitive types
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included in the resource system: integers, colors, strings, references to
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other resources, etc. Complex resources, such as bitmaps and XML
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describes, are stored as a primitive string resource whose value is the path
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of the underlying Asset holding its actual data.</p>
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<p><b>Bag Resource</b>: A special kind of resource entry that, instead of a
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simple string, holds an arbitrary list of name/value pairs. Each name is
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itself a resource identifier, and each value can hold
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the same kinds of string formatted data as a normal resource. Bags also
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support inheritance: a bag can inherit the values from another bag, selectively
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replacing or extending them to generate its own contents.</p>
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<p><b>Kind</b>: The resource kind is a way to organize resource identifiers
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for various purposes. For example, drawable resources are used to
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instantiate Drawable objects, so their data is a primitive resource containing
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either a color constant or string path to a bitmap or XML asset. Other
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common resource kinds are string (localized string primitives), color
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(color primitives), layout (a string path to an XML asset describing a view
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layout), and style (a bag resource describing user interface attributes).
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There is also a standard "attr" resource kind, which defines the resource
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identifiers to be used for naming bag items and XML attributes</p>
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<p><b>Style</b>: The name of the resource kind containing bags that are used
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to supply a set of user interface attributes. For example, a TextView class may
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be given a style resource that defines its text size, color, and alignment.
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In a layout XML file, you associate a style with a bag using the "style"
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attribute, whose value is the name of the style resource.</p>
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<p><b>Style Class</b>: Specifies a related set of attribute resources.
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This data is not placed in the resource table itself, but used to generate
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Java constants that make it easier for you to retrieve values out of
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a style resource and/or XML tag's attributes. For example, the
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Android platform defines a "View" style class that
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contains all of the standard view attributes: padding, visibility,
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background, etc.; when View is inflated it uses this style class to
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retrieve those values from the XML file (at which point style and theme
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information is applied as approriate) and load them into its instance.</p>
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<p><b>Configuration</b>: For any particular resource identifier, there may be
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multiple different available values depending on the current configuration.
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The configuration includes the locale (language and country), screen
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orientation, screen density, etc. The current configuration is used to
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select which resource values are in effect when the resource table is
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loaded.</p>
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<p><b>Theme</b>: A standard style resource that supplies global
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attribute values for a particular context. For example, when writing a
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Activity the application developer can select a standard theme to use, such
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as the Theme.White or Theme.Black styles; this style supplies information
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such as the screen background image/color, default text color, button style,
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text editor style, text size, etc. When inflating a layout resource, most
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values for widgets (the text color, selector, background) if not explicitly
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set will come from the current theme; style and attribute
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values supplied in the layout can also assign their value from explicitly
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named values in the theme attributes if desired.</p>
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<p><b>Overlay</b>: A resource table that does not define a new set of resources,
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but instead replaces the values of resources that are in another resource table.
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Like a configuration, this is applied at load time
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to the resource data; it can add new configuration values (for example
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strings in a new locale), replace existing values (for example change
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the standard white background image to a "Hello Kitty" background image),
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and modify resource bags (for example change the font size of the Theme.White
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style to have an 18 pt font size). This is the facility that allows the
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user to select between different global appearances of their device, or
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download files with new appearances.</p>
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<a name="ResourcesQuickStart"></a>
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<h3>Examples</h3>
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<p>This section gives a few quick examples you can use to make your own resources.
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For more details on how to define and use resources, see <a
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href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources and
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Internationalization</a>. </p>
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<a name="UsingSystemResources"></a>
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<h4>Using System Resources</h4>
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<p>Many resources included with the system are available to applications.
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All such resources are defined under the class "android.R". For example,
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you can display the standard application icon in a screen with the following
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code:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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requestScreenFeatures(FEATURE_BADGE_IMAGE);
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super.onStart();
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setBadgeResource(android.R.drawable.sym_def_app_icon);
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}
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}
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</pre>
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<p>In a similar way, this code will apply to your screen the standard
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"green background" visual treatment defined by the system:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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super.onStart();
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setTheme(android.R.style.Theme_Black);
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}
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}
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</pre>
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<a name="StringResources"></a>
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<h4>String Resources</h4>
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<p>String resources are defined using an XML resource description syntax.
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The file or multiple files containing these resources can be given any name
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(as long as it has a .xml suffix) and placed at an appropriate location in
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the source tree for the desired configuration (locale/orientation/density).
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<p>Here is a simple resource file describing a few strings:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<resources>
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<string id="mainLabel">Hello <u>th<ignore>e</ignore>re</u>, <i>you</i> <b>Activity</b>!</string>
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<string id="back">Back</string>
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<string id="clear">Clear</string>
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</resources>
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</pre>
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<p>Typically this file will be called "strings.xml", and must be placed
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in the <code>values</code> directory:</p>
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<pre>
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MyApp/res/values/strings.xml
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</pre>
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<p>The strings can now be retrieved by your application through the
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symbol specified in the "id" attribute:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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super.onStart();
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String back = getResources().getString(R.string.back).toString();
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back = getString(R.string.back).toString(); // synonym
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}
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}
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</pre>
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<p>Unlike system resources, the resource symbol (the R class) we are using
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here comes from our own application's package, not android.R.</p>
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<p>Note that the "mainLabel" string is complex, including style information.
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To support this, the <code>getString()</code> method returns a
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<code>CharSequence</code> object that you can pass to a
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<code>TextView</code> to retain those style. This is why code
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must call <code>toString()</code> on the returned resource if it wants
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a raw string.</p>
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<a name="ColorResources"></a>
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<h4>Color Resources</h4>
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<p>Color resources are created in a way very similar to string resources,
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but with the <color> resource tag. The data for these resources
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must be a hex color constant of the form "#rgb", "#argb", "#rrggbb", or
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"#aarrggbb". The alpha channel is 0xff (or 0xf) for opaque and 0
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for transparent.</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<resources>
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<color id="opaque_red">#ffff0000</color>
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<color id="transparent_red">#80ff0000</color>
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<color id="opaque_blue">#0000ff</color>
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<color id="opaque_green">#0f0</color>
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</resources>
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</pre>
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<p>While color definitions could be placed in the same resource file
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as the previously shown string data, usually you will place the colors in
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their own file:</p>
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<pre>
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MyApp/res/values/colors.xml
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</pre>
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<p>The colors can now be retrieved by your application through the
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symbol specified in the "id" attribute:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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super.onStart();
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int red = getResources().getColor(R.color.opaque_red);
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}
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}
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</pre>
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<a name="DrawableResources"></a>
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<h4>Drawable Resources</h4>
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<p>For simple drawable resources, all you need to do is place your
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image in a special resource sub-directory called "drawable". Files here
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are things that can be handled by an implementation of the
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{@link android.graphics.drawable.Drawable Drawable} class, often bitmaps
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(such as PNG images) but also various kinds of XML descriptions
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for selectors, gradients, etc.</p>
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<p>The drawable files will be scanned by the
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resource tool, automatically generating a resource entry for each found.
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For example the file <code>res/drawable/<myimage>.<ext></code>
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will result in a resource symbol named "myimage" (without the extension). Note
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that these file names <em>must</em> be valid Java identifiers, and should
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have only lower-case letters.</p>
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<p>For example, to use your own custom image as a badge in a screen,
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you can place the image here:</p>
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<pre>
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MyApp/res/drawable/my_badge.png
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</pre>
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<p>The image can then be used in your code like this:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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requestScreenFeatures(FEATURE_BADGE_IMAGE);
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super.onStart();
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setBadgeResource(R.drawable.my_badge);
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}
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}
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</pre>
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<p>For drawables that are a single solid color, you can also define them
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in a resource file very much like colors shown previously. The only
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difference is that here we use the <drawable> tag to create a
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drawable resource.</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<resources>
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<drawable id="opaque_red">#ffff0000</drawable>
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<drawable id="transparent_red">#80ff0000</drawable>
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<drawable id="opaque_blue">#0000ff</drawable>
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<drawable id="opaque_green">#0f0</drawable>
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</resources>
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</pre>
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<p>These resource entries are often placed in the same resource file
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as color definitions:</p>
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<pre>
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MyApp/res/values/colors.xml
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</pre>
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<a name="LayoutResources"></a>
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<h4>Layout Resources</h4>
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<p>Layout resources describe a view hierarchy configuration that is
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generated at runtime. These resources are XML files placed in the
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resource directory "layout", and are how you should create the content
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views inside of your screen (instead of creating them by hand) so that
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they can be themed, styled, configured, and overlayed.</p>
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<p>Here is a simple layout resource consisting of a single view, a text
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editor:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<root>
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<EditText id="text"
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android:layout_width="fill-parent" android:layout_height="fill-parent"
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android:text="Hello, World!" />
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</root>
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</pre>
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<p>To use this layout, it can be placed in a file like this:</p>
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<pre>
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MyApp/res/layout/my_layout.xml
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</pre>
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<p>The layout can then be instantiated in your screen like this:</p>
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<pre class="prettyprint">
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public class MyActivity extends Activity
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{
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public void onStart()
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{
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super.onStart();
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setContentView(R.layout.my_layout);
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}
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}
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</pre>
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<p>Note that there are a number of visual attributes that can be supplied
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to TextView (including textSize, textColor, and textStyle) that we did
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not define in the previous example; in such a sitation, the default values for
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those attributes come from the theme. If we want to customize them, we
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can supply them explicitly in the XML file:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<root>
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<EditText id="text"
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android:layout_width="match_parent" android:layout_height="match_parent"
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<b>android:textSize="18" android:textColor="#008"</b>
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android:text="Hello, World!" />
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</root>
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</pre>
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<p>However, usually these kinds of attributes (those being attributes that
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usually make sense to vary with theme or overlay) should be defined through
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the theme or separate style resource. Later we will see how this is done.</p>
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<a name="ReferencesToResources"></a>
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<h4>References to Resources</h4>
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<p>A value supplied in an attribute (or resource) can also be a reference to
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a resource. This is often used in layout files to supply strings (so they
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can be localized) and images (which exist in another file), though a reference
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can be do any resource type including colors and integers.</p>
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<p>For example, if we have the previously defined color resources, we can
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write a layout file that sets the text color size to be the value contained in
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one of those resources:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<root>
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<EditText id="text"
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android:layout_width="match_parent" android:layout_height="match_parent"
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<b>android:textColor="@color/opaque_red"</b>
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android:text="Hello, World!" />
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</root>
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</pre>
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<p>Note here the use of the '@' prefix to introduce a resource reference -- the
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text following that is the name of a resource in the form
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of <code>@[package:]type/name</code>. In this case we didn't need to specify
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the package because we are referencing a resource in our own package. To
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reference a system resource, you would need to write:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<root>
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<EditText id="text"
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android:layout_width="match_parent" android:layout_height="match_parent"
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android:textColor="@<b>android:</b>color/opaque_red"
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android:text="Hello, World!" />
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</root>
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</pre>
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<p>As another example, you should always use resource references when supplying
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strings in a layout file so that they can be localized:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<root>
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<EditText id="text"
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android:layout_width="match_parent" android:layout_height="match_parent"
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android:textColor="@android:color/opaque_red"
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android:text="@string/hello_world" />
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</root>
|
|
</pre>
|
|
|
|
<p>This facility can also be used to create references between resources.
|
|
For example, we can create new drawable resources that are aliases for
|
|
existing images:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<resources>
|
|
<drawable id="my_background">@android:drawable/theme2_background</drawable>
|
|
</resources>
|
|
</pre>
|
|
|
|
<a name="ReferencesToThemeAttributes"></a>
|
|
<h4>References to Theme Attributes</h4>
|
|
|
|
<p>Another kind of resource value allows you to reference the value of an
|
|
attribute in the current theme. This attribute reference can <em>only</em>
|
|
be used in style resources and XML attributes; it allows you to customize the
|
|
look of UI elements by changing them to standard variations supplied by the
|
|
current theme, instead of supplying more concrete values.</p>
|
|
|
|
<p>As an example, we can use this in our layout to set the text color to
|
|
one of the standard colors defined in the base system theme:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<root>
|
|
<EditText id="text"
|
|
android:layout_width="match_parent" android:layout_height="match_parent"
|
|
<b>android:textColor="?android:textDisabledColor"</b>
|
|
android:text="@string/hello_world" />
|
|
</root>
|
|
</pre>
|
|
|
|
<p>Note that this is very similar to a resource reference, except we are using
|
|
an '?' prefix instead of '@'. When you use this markup, you are supplying
|
|
the name of an attribute resource that will be looked up in the theme --
|
|
because the resource tool knows that an attribute resource is expected,
|
|
you do not need to explicitly state the type (which would be
|
|
<code>?android:attr/android:textDisabledColor</code>).</p>
|
|
|
|
<p>Other than using this resource identifier to find the value in the
|
|
theme instead of raw resources, the name syntax is identical to the '@' format:
|
|
<code>?[package:]type/name</code> with the type here being optional.</p>
|
|
|
|
<a name="StyleResources"></a>
|
|
<h4>Style Resources</h4>
|
|
|
|
<p>A style resource is a set of name/value pairs describing a group
|
|
of related attributes. There are two main uses for these resources:
|
|
defining overall visual themes, and describing a set of visual attributes
|
|
to apply to a class in a layout resource. In this section we will look
|
|
at their use to describe themes; later we will look at using them in
|
|
conjunction with layouts.</p>
|
|
|
|
<p>Like strings, styles are defined through a resource XML file. In the
|
|
situation where we want to define a new theme, we can create a custom theme
|
|
style that inherits from one of the standard system themes:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<resources>
|
|
<style id="Theme" parent="android:Theme.White">
|
|
<item id="android:foregroundColor">#FFF8D96F</item>
|
|
<item id="android:textColor">@color/opaque_blue</item>
|
|
<item id="android:textSelectedColor">?android:textColor</item>
|
|
</style>
|
|
</resources>
|
|
</pre>
|
|
|
|
<p>Typically these resource definitions will be placed in a file
|
|
called "styles.xml" , and must be placed in the <code>values</code>
|
|
directory:</p>
|
|
|
|
<pre>
|
|
MyApp/res/values/styles.xml
|
|
</pre>
|
|
|
|
<p>Similar to how we previously used a system style for an Activity theme,
|
|
you can apply this style to your Activity:</p>
|
|
|
|
<pre class="prettyprint">
|
|
public class MyActivity extends Activity
|
|
{
|
|
public void onStart()
|
|
{
|
|
super.onStart();
|
|
|
|
setTheme(R.style.Theme);
|
|
}
|
|
}
|
|
</pre>
|
|
|
|
<p>In the style resource shown here, we used the <code>parent</code>
|
|
attribute to specify another style resource from which it inherits
|
|
its values -- in this case the <code>Theme.White</code> system resource:</p>
|
|
|
|
<pre>
|
|
<style id="Home" parent="android:Theme.White">
|
|
...
|
|
</style>
|
|
</pre>
|
|
|
|
<p>Note, when doing this, that you must use the "android" prefix in front
|
|
to tell the compiler the namespace to look in for the resource --
|
|
the resources you are specifying here are in your application's namespace,
|
|
not the system. This explicit namespace specification ensures that names
|
|
the application uses will not accidentally conflict with those defined by
|
|
the system.</p>
|
|
|
|
<p>If you don't specify an explicit parent style, it will be inferred
|
|
from the style name -- everything before the final '.' in the name of the
|
|
style being defined is taken as the parent style name. Thus, to make
|
|
another style in your application that inherits from this base Theme style,
|
|
you can write:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<resources>
|
|
<style id="Theme.WhiteText">
|
|
<item id="android:foregroundColor">#FFFFFFFF</item>
|
|
<item id="android:textColor">?android:foregroundColor</item>
|
|
</style>
|
|
</resources>
|
|
</pre>
|
|
|
|
<p>This results in the symbol <code>R.style.Theme_WhiteText</code> that
|
|
can be used in Java just like we did with <code>R.style.Theme</code>
|
|
above.</p>
|
|
|
|
<a name="StylesInLayoutResources"></a>
|
|
<h4>Styles in Layout Resources</h4>
|
|
|
|
<p>Often you will have a number fo views in a layout that all use the same
|
|
set of attributes, or want to allow resource overlays to modify the values of
|
|
attributes. Style resources can be used for both of these purposes, to put
|
|
attribute definitions in a single place that can be references by multiple
|
|
XML tags and modified by overlays. To do this, you simply define a
|
|
new style resource with the desired values:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<resources>
|
|
<style id="SpecialText">
|
|
<item id="android:textSize">18</item>
|
|
<item id="android:textColor">#008</item>
|
|
</style>
|
|
</resources>
|
|
</pre>
|
|
|
|
<p>You can now apply this style to your TextView in the XML file:</p>
|
|
|
|
<pre>
|
|
<?xml version="1.0" encoding="utf-8"?>
|
|
<root>
|
|
<EditText id="text1" <b>style="@style/SpecialText"</b>
|
|
android:layout_width="match_parent" android:layout_height="wrap_content"
|
|
android:text="Hello, World!" />
|
|
<EditText id="text2" <b>style="@style/SpecialText"</b>
|
|
android:layout_width="match_parent" android:layout_height="wrap_content"
|
|
android:text="I love you all." />
|
|
</root></pre>
|
|
<h4> </h4>
|
|
|
|
</body>
|
|
</html>
|
|
|