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9 <p>Contains classes for accessing and publishing data
10 on the device. It includes three main categories of APIs:
11 the {@link android.content.res.Resources Resources} for
12 retrieving resource data associated with an application;
13 {@link android.content.ContentProvider Content Providers} and
14 {@link android.content.ContentResolver ContentResolver} for managing and
15 publishing persistent data associated with an application; and
16 the {@link android.content.pm.PackageManager Package Manager}
17 for finding out information about the application packages installed
20 <p>In addition, the {@link android.content.Context Context} abstract class
21 is a base API for pulling these pieces together, allowing you to access
22 an application's resources and transfer data between applications.</p>
24 <p>This package builds on top of the lower-level Android packages
25 {@link android.database}, {@link android.text},
26 {@link android.graphics.drawable}, {@link android.graphics},
27 {@link android.os}, and {@link android.util}.</p>
30 <li> <a href="#Resources">Resources</a>
32 <li> <a href="#ResourcesTerminology">Terminology</a>
33 <li> <a href="#ResourcesQuickStart">Examples</a>
35 <li> <a href="#UsingSystemResources">Using System Resources</a>
36 <li> <a href="#StringResources">String Resources</a>
37 <li> <a href="#ColorResources">Color Resources</a>
38 <li> <a href="#DrawableResources">Drawable Resources</a>
39 <li> <a href="#LayoutResources">Layout Resources</a>
40 <li> <a href="#ReferencesToResources">References to Resources</a>
41 <li> <a href="#ReferencesToThemeAttributes">References to Theme Attributes</a>
42 <li> <a href="#StyleResources">Style Resources</a>
43 <li> <a href="#StylesInLayoutResources">Styles in Layout Resources</a>
48 <a name="Resources"></a>
51 <p>This topic includes a terminology list associated with resources, and a series
52 of examples of using resources in code. For a complete guide on creating and
53 using resources, see the document on <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources
54 and Internationalization</a>. For a reference on the supported Android resource types,
55 see <a href="{@docRoot}guide/topics/resources/available-resources.html">Available Resource Types</a>.</p>
56 <p>The Android resource system keeps track of all non-code
57 assets associated with an application. You use the
58 {@link android.content.res.Resources Resources} class to access your
59 application's resources; the Resources instance associated with your
60 application can generally be found through
61 {@link android.content.Context#getResources Context.getResources()}.</p>
62 <p>An application's resources are compiled into the application
63 binary at build time for you by the build system. To use a resource,
64 you must install it correctly in the source tree and build your
65 application. As part of the build process, Java symbols for each
66 of the resources are generated that you can use in your source
67 code -- this allows the compiler to verify that your application code matches
68 up with the resources you defined.</p>
70 <p>The rest of this section is organized as a tutorial on how to
71 use resources in an application.</p>
73 <a name="ResourcesTerminology"></a>
76 <p>The resource system brings a number of different pieces together to
77 form the final complete resource functionality. To help understand the
78 overall system, here are some brief definitions of the core concepts and
79 components you will encounter in using it:</p>
81 <p><b>Asset</b>: A single blob of data associated with an application. This
82 includes Java object files, graphics (such as PNG images), XML files, etc.
83 These files are organized in a directory hierarchy that, during final packaging
84 of the application, is bundled together into a single ZIP file.</p>
86 <p><b>aapt</b>: The tool that generates the final ZIP file of application
87 assets. In addition to collecting raw assets together, it also parses
88 resource definitions into binary asset data.</p>
90 <p><b>Resource Table</b>: A special asset that aapt generates for you,
91 describing all of the resources contained in an application/package.
92 This file is accessed for you by the Resources class; it is not touched
93 directly by applications.</p>
95 <p><b>Resource</b>: An entry in the Resource Table describing a single
96 named value. Broadly, there are two types of resources: primitives and
99 <p><b>Resource Identifier</b>: In the Resource Table all resources are
100 identified by a unique integer number. In source code (resource descriptions,
101 XML files, Java code) you can use symbolic names that stand as constants for
102 the actual resource identifier integer.</p>
104 <p><b>Primitive Resource</b>: All primitive resources can be written as a
105 simple string, using formatting to describe a variety of primitive types
106 included in the resource system: integers, colors, strings, references to
107 other resources, etc. Complex resources, such as bitmaps and XML
108 describes, are stored as a primitive string resource whose value is the path
109 of the underlying Asset holding its actual data.</p>
111 <p><b>Bag Resource</b>: A special kind of resource entry that, instead of a
112 simple string, holds an arbitrary list of name/value pairs. Each name is
113 itself a resource identifier, and each value can hold
114 the same kinds of string formatted data as a normal resource. Bags also
115 support inheritance: a bag can inherit the values from another bag, selectively
116 replacing or extending them to generate its own contents.</p>
118 <p><b>Kind</b>: The resource kind is a way to organize resource identifiers
119 for various purposes. For example, drawable resources are used to
120 instantiate Drawable objects, so their data is a primitive resource containing
121 either a color constant or string path to a bitmap or XML asset. Other
122 common resource kinds are string (localized string primitives), color
123 (color primitives), layout (a string path to an XML asset describing a view
124 layout), and style (a bag resource describing user interface attributes).
125 There is also a standard "attr" resource kind, which defines the resource
126 identifiers to be used for naming bag items and XML attributes</p>
128 <p><b>Style</b>: The name of the resource kind containing bags that are used
129 to supply a set of user interface attributes. For example, a TextView class may
130 be given a style resource that defines its text size, color, and alignment.
131 In a layout XML file, you associate a style with a bag using the "style"
132 attribute, whose value is the name of the style resource.</p>
134 <p><b>Style Class</b>: Specifies a related set of attribute resources.
135 This data is not placed in the resource table itself, but used to generate
136 Java constants that make it easier for you to retrieve values out of
137 a style resource and/or XML tag's attributes. For example, the
138 Android platform defines a "View" style class that
139 contains all of the standard view attributes: padding, visibility,
140 background, etc.; when View is inflated it uses this style class to
141 retrieve those values from the XML file (at which point style and theme
142 information is applied as approriate) and load them into its instance.</p>
144 <p><b>Configuration</b>: For any particular resource identifier, there may be
145 multiple different available values depending on the current configuration.
146 The configuration includes the locale (language and country), screen
147 orientation, screen density, etc. The current configuration is used to
148 select which resource values are in effect when the resource table is
151 <p><b>Theme</b>: A standard style resource that supplies global
152 attribute values for a particular context. For example, when writing a
153 Activity the application developer can select a standard theme to use, such
154 as the Theme.White or Theme.Black styles; this style supplies information
155 such as the screen background image/color, default text color, button style,
156 text editor style, text size, etc. When inflating a layout resource, most
157 values for widgets (the text color, selector, background) if not explicitly
158 set will come from the current theme; style and attribute
159 values supplied in the layout can also assign their value from explicitly
160 named values in the theme attributes if desired.</p>
162 <p><b>Overlay</b>: A resource table that does not define a new set of resources,
163 but instead replaces the values of resources that are in another resource table.
164 Like a configuration, this is applied at load time
165 to the resource data; it can add new configuration values (for example
166 strings in a new locale), replace existing values (for example change
167 the standard white background image to a "Hello Kitty" background image),
168 and modify resource bags (for example change the font size of the Theme.White
169 style to have an 18 pt font size). This is the facility that allows the
170 user to select between different global appearances of their device, or
171 download files with new appearances.</p>
173 <a name="ResourcesQuickStart"></a>
176 <p>This section gives a few quick examples you can use to make your own resources.
177 For more details on how to define and use resources, see <a
178 href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources and
179 Internationalization</a>. </p>
181 <a name="UsingSystemResources"></a>
182 <h4>Using System Resources</h4>
184 <p>Many resources included with the system are available to applications.
185 All such resources are defined under the class "android.R". For example,
186 you can display the standard application icon in a screen with the following
189 <pre class="prettyprint">
190 public class MyActivity extends Activity
192 public void onStart()
194 requestScreenFeatures(FEATURE_BADGE_IMAGE);
198 setBadgeResource(android.R.drawable.sym_def_app_icon);
203 <p>In a similar way, this code will apply to your screen the standard
204 "green background" visual treatment defined by the system:</p>
206 <pre class="prettyprint">
207 public class MyActivity extends Activity
209 public void onStart()
213 setTheme(android.R.style.Theme_Black);
218 <a name="StringResources"></a>
219 <h4>String Resources</h4>
221 <p>String resources are defined using an XML resource description syntax.
222 The file or multiple files containing these resources can be given any name
223 (as long as it has a .xml suffix) and placed at an appropriate location in
224 the source tree for the desired configuration (locale/orientation/density).
226 <p>Here is a simple resource file describing a few strings:</p>
229 <?xml version="1.0" encoding="utf-8"?>
231 <string id="mainLabel">Hello <u>th<ignore>e</ignore>re</u>, <i>you</i> <b>Activity</b>!</string>
232 <string id="back">Back</string>
233 <string id="clear">Clear</string>
237 <p>Typically this file will be called "strings.xml", and must be placed
238 in the <code>values</code> directory:</p>
241 MyApp/res/values/strings.xml
244 <p>The strings can now be retrieved by your application through the
245 symbol specified in the "id" attribute:</p>
247 <pre class="prettyprint">
248 public class MyActivity extends Activity
250 public void onStart()
254 String back = getResources().getString(R.string.back).toString();
255 back = getString(R.string.back).toString(); // synonym
260 <p>Unlike system resources, the resource symbol (the R class) we are using
261 here comes from our own application's package, not android.R.</p>
263 <p>Note that the "mainLabel" string is complex, including style information.
264 To support this, the <code>getString()</code> method returns a
265 <code>CharSequence</code> object that you can pass to a
266 <code>TextView</code> to retain those style. This is why code
267 must call <code>toString()</code> on the returned resource if it wants
270 <a name="ColorResources"></a>
271 <h4>Color Resources</h4>
273 <p>Color resources are created in a way very similar to string resources,
274 but with the <color> resource tag. The data for these resources
275 must be a hex color constant of the form "#rgb", "#argb", "#rrggbb", or
276 "#aarrggbb". The alpha channel is 0xff (or 0xf) for opaque and 0
280 <?xml version="1.0" encoding="utf-8"?>
282 <color id="opaque_red">#ffff0000</color>
283 <color id="transparent_red">#80ff0000</color>
284 <color id="opaque_blue">#0000ff</color>
285 <color id="opaque_green">#0f0</color>
289 <p>While color definitions could be placed in the same resource file
290 as the previously shown string data, usually you will place the colors in
294 MyApp/res/values/colors.xml
297 <p>The colors can now be retrieved by your application through the
298 symbol specified in the "id" attribute:</p>
300 <pre class="prettyprint">
301 public class MyActivity extends Activity
303 public void onStart()
307 int red = getResources().getColor(R.color.opaque_red);
312 <a name="DrawableResources"></a>
313 <h4>Drawable Resources</h4>
315 <p>For simple drawable resources, all you need to do is place your
316 image in a special resource sub-directory called "drawable". Files here
317 are things that can be handled by an implementation of the
318 {@link android.graphics.drawable.Drawable Drawable} class, often bitmaps
319 (such as PNG images) but also various kinds of XML descriptions
320 for selectors, gradients, etc.</p>
322 <p>The drawable files will be scanned by the
323 resource tool, automatically generating a resource entry for each found.
324 For example the file <code>res/drawable/<myimage>.<ext></code>
325 will result in a resource symbol named "myimage" (without the extension). Note
326 that these file names <em>must</em> be valid Java identifiers, and should
327 have only lower-case letters.</p>
329 <p>For example, to use your own custom image as a badge in a screen,
330 you can place the image here:</p>
333 MyApp/res/drawable/my_badge.png
336 <p>The image can then be used in your code like this:</p>
338 <pre class="prettyprint">
339 public class MyActivity extends Activity
341 public void onStart()
343 requestScreenFeatures(FEATURE_BADGE_IMAGE);
347 setBadgeResource(R.drawable.my_badge);
352 <p>For drawables that are a single solid color, you can also define them
353 in a resource file very much like colors shown previously. The only
354 difference is that here we use the <drawable> tag to create a
355 drawable resource.</p>
358 <?xml version="1.0" encoding="utf-8"?>
360 <drawable id="opaque_red">#ffff0000</drawable>
361 <drawable id="transparent_red">#80ff0000</drawable>
362 <drawable id="opaque_blue">#0000ff</drawable>
363 <drawable id="opaque_green">#0f0</drawable>
367 <p>These resource entries are often placed in the same resource file
368 as color definitions:</p>
371 MyApp/res/values/colors.xml
374 <a name="LayoutResources"></a>
375 <h4>Layout Resources</h4>
377 <p>Layout resources describe a view hierarchy configuration that is
378 generated at runtime. These resources are XML files placed in the
379 resource directory "layout", and are how you should create the content
380 views inside of your screen (instead of creating them by hand) so that
381 they can be themed, styled, configured, and overlayed.</p>
383 <p>Here is a simple layout resource consisting of a single view, a text
387 <?xml version="1.0" encoding="utf-8"?>
389 <EditText id="text"
390 android:layout_width="fill-parent" android:layout_height="fill-parent"
391 android:text="Hello, World!" />
395 <p>To use this layout, it can be placed in a file like this:</p>
398 MyApp/res/layout/my_layout.xml
401 <p>The layout can then be instantiated in your screen like this:</p>
403 <pre class="prettyprint">
404 public class MyActivity extends Activity
406 public void onStart()
409 setContentView(R.layout.my_layout);
414 <p>Note that there are a number of visual attributes that can be supplied
415 to TextView (including textSize, textColor, and textStyle) that we did
416 not define in the previous example; in such a sitation, the default values for
417 those attributes come from the theme. If we want to customize them, we
418 can supply them explicitly in the XML file:</p>
421 <?xml version="1.0" encoding="utf-8"?>
423 <EditText id="text"
424 android:layout_width="match_parent" android:layout_height="match_parent"
425 <b>android:textSize="18" android:textColor="#008"</b>
426 android:text="Hello, World!" />
430 <p>However, usually these kinds of attributes (those being attributes that
431 usually make sense to vary with theme or overlay) should be defined through
432 the theme or separate style resource. Later we will see how this is done.</p>
434 <a name="ReferencesToResources"></a>
435 <h4>References to Resources</h4>
437 <p>A value supplied in an attribute (or resource) can also be a reference to
438 a resource. This is often used in layout files to supply strings (so they
439 can be localized) and images (which exist in another file), though a reference
440 can be do any resource type including colors and integers.</p>
442 <p>For example, if we have the previously defined color resources, we can
443 write a layout file that sets the text color size to be the value contained in
444 one of those resources:</p>
447 <?xml version="1.0" encoding="utf-8"?>
449 <EditText id="text"
450 android:layout_width="match_parent" android:layout_height="match_parent"
451 <b>android:textColor="@color/opaque_red"</b>
452 android:text="Hello, World!" />
456 <p>Note here the use of the '@' prefix to introduce a resource reference -- the
457 text following that is the name of a resource in the form
458 of <code>@[package:]type/name</code>. In this case we didn't need to specify
459 the package because we are referencing a resource in our own package. To
460 reference a system resource, you would need to write:</p>
463 <?xml version="1.0" encoding="utf-8"?>
465 <EditText id="text"
466 android:layout_width="match_parent" android:layout_height="match_parent"
467 android:textColor="@<b>android:</b>color/opaque_red"
468 android:text="Hello, World!" />
472 <p>As another example, you should always use resource references when supplying
473 strings in a layout file so that they can be localized:</p>
476 <?xml version="1.0" encoding="utf-8"?>
478 <EditText id="text"
479 android:layout_width="match_parent" android:layout_height="match_parent"
480 android:textColor="@android:color/opaque_red"
481 android:text="@string/hello_world" />
485 <p>This facility can also be used to create references between resources.
486 For example, we can create new drawable resources that are aliases for
490 <?xml version="1.0" encoding="utf-8"?>
492 <drawable id="my_background">@android:drawable/theme2_background</drawable>
496 <a name="ReferencesToThemeAttributes"></a>
497 <h4>References to Theme Attributes</h4>
499 <p>Another kind of resource value allows you to reference the value of an
500 attribute in the current theme. This attribute reference can <em>only</em>
501 be used in style resources and XML attributes; it allows you to customize the
502 look of UI elements by changing them to standard variations supplied by the
503 current theme, instead of supplying more concrete values.</p>
505 <p>As an example, we can use this in our layout to set the text color to
506 one of the standard colors defined in the base system theme:</p>
509 <?xml version="1.0" encoding="utf-8"?>
511 <EditText id="text"
512 android:layout_width="match_parent" android:layout_height="match_parent"
513 <b>android:textColor="?android:textDisabledColor"</b>
514 android:text="@string/hello_world" />
518 <p>Note that this is very similar to a resource reference, except we are using
519 an '?' prefix instead of '@'. When you use this markup, you are supplying
520 the name of an attribute resource that will be looked up in the theme --
521 because the resource tool knows that an attribute resource is expected,
522 you do not need to explicitly state the type (which would be
523 <code>?android:attr/android:textDisabledColor</code>).</p>
525 <p>Other than using this resource identifier to find the value in the
526 theme instead of raw resources, the name syntax is identical to the '@' format:
527 <code>?[package:]type/name</code> with the type here being optional.</p>
529 <a name="StyleResources"></a>
530 <h4>Style Resources</h4>
532 <p>A style resource is a set of name/value pairs describing a group
533 of related attributes. There are two main uses for these resources:
534 defining overall visual themes, and describing a set of visual attributes
535 to apply to a class in a layout resource. In this section we will look
536 at their use to describe themes; later we will look at using them in
537 conjunction with layouts.</p>
539 <p>Like strings, styles are defined through a resource XML file. In the
540 situation where we want to define a new theme, we can create a custom theme
541 style that inherits from one of the standard system themes:</p>
544 <?xml version="1.0" encoding="utf-8"?>
546 <style id="Theme" parent="android:Theme.White">
547 <item id="android:foregroundColor">#FFF8D96F</item>
548 <item id="android:textColor">@color/opaque_blue</item>
549 <item id="android:textSelectedColor">?android:textColor</item>
554 <p>Typically these resource definitions will be placed in a file
555 called "styles.xml" , and must be placed in the <code>values</code>
559 MyApp/res/values/styles.xml
562 <p>Similar to how we previously used a system style for an Activity theme,
563 you can apply this style to your Activity:</p>
565 <pre class="prettyprint">
566 public class MyActivity extends Activity
568 public void onStart()
572 setTheme(R.style.Theme);
577 <p>In the style resource shown here, we used the <code>parent</code>
578 attribute to specify another style resource from which it inherits
579 its values -- in this case the <code>Theme.White</code> system resource:</p>
582 <style id="Home" parent="android:Theme.White">
587 <p>Note, when doing this, that you must use the "android" prefix in front
588 to tell the compiler the namespace to look in for the resource --
589 the resources you are specifying here are in your application's namespace,
590 not the system. This explicit namespace specification ensures that names
591 the application uses will not accidentally conflict with those defined by
594 <p>If you don't specify an explicit parent style, it will be inferred
595 from the style name -- everything before the final '.' in the name of the
596 style being defined is taken as the parent style name. Thus, to make
597 another style in your application that inherits from this base Theme style,
601 <?xml version="1.0" encoding="utf-8"?>
603 <style id="Theme.WhiteText">
604 <item id="android:foregroundColor">#FFFFFFFF</item>
605 <item id="android:textColor">?android:foregroundColor</item>
610 <p>This results in the symbol <code>R.style.Theme_WhiteText</code> that
611 can be used in Java just like we did with <code>R.style.Theme</code>
614 <a name="StylesInLayoutResources"></a>
615 <h4>Styles in Layout Resources</h4>
617 <p>Often you will have a number fo views in a layout that all use the same
618 set of attributes, or want to allow resource overlays to modify the values of
619 attributes. Style resources can be used for both of these purposes, to put
620 attribute definitions in a single place that can be references by multiple
621 XML tags and modified by overlays. To do this, you simply define a
622 new style resource with the desired values:</p>
625 <?xml version="1.0" encoding="utf-8"?>
627 <style id="SpecialText">
628 <item id="android:textSize">18</item>
629 <item id="android:textColor">#008</item>
634 <p>You can now apply this style to your TextView in the XML file:</p>
637 <?xml version="1.0" encoding="utf-8"?>
639 <EditText id="text1" <b>style="@style/SpecialText"</b>
640 android:layout_width="match_parent" android:layout_height="wrap_content"
641 android:text="Hello, World!" />
642 <EditText id="text2" <b>style="@style/SpecialText"</b>
643 android:layout_width="match_parent" android:layout_height="wrap_content"
644 android:text="I love you all." />