providing-resources.jd revision 7ef674b596ba1bac6b26350a6c478d5e6a16bfd7
1page.title=Providing Resources 2parent.title=Application Resources 3parent.link=index.html 4@jd:body 5 6<div id="qv-wrapper"> 7<div id="qv"> 8 <h2>Quickview</h2> 9 <ul> 10 <li>Different types of resources belong in different subdirectories of {@code res/}</li> 11 <li>Alternative resources provide configuration-specific resource files</li> 12 <li>Always include default resources so your app does not depend on specific configurations</li> 13 </ul> 14 <h2>In this document</h2> 15 <ol> 16 <li><a href="#ResourceTypes">Grouping Resource Types</a></li> 17 <li><a href="#AlternativeResources">Providing Alternative Resources</a> 18 <ol> 19 <li><a href="#QualifierRules">Qualifier name rules</a></li> 20 <li><a href="#AliasResources">Creating alias resources</a></li> 21 </ol> 22 </li> 23 <li><a href="#Compatibility">Providing the Best Device Compatibility with Resources</a></li> 24 <li><a href="#BestMatch">How Android Finds the Best-matching Resource</a></li> 25 <li><a href="#KnownIssues">Known Issues</a></li> 26 </ol> 27 28 <h2>See also</h2> 29 <ol> 30 <li><a href="accessing-resources.html">Accessing Resources</a></li> 31 <li><a href="available-resources.html">Resource Types</a></li> 32 <li><a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 33Screens</a></li> 34 </ol> 35</div> 36</div> 37 38<p>You should always externalize application resources such as images and strings from your 39code, so that you can maintain them independently. You can also provide alternative resources for 40specific device configurations, by grouping them in specially-named resource directories. Android 41then applies the appropriate resource based on the current configuration. For 42instance, you might want to provide a different UI layout depending on the screen size.</p> 43 44<p>Once you externalize your application resources, you can access them 45using resource IDs that are generated in your project's {@code R} class. How to use 46resources in your application is discussed in <a href="accessing-resources.html">Accessing 47Resources</a>. This document shows you how to group your resources in your Android project and 48provide alternative resources for specific device configurations.</p> 49 50 51<h2 id="ResourceTypes">Grouping Resource Types</h2> 52 53<p>You should place each type of resource in a specific subdirectory of your project's 54{@code res/} directory. For example, here's the file hierarchy for a simple project:</p> 55 56<pre class="classic no-pretty-print"> 57MyProject/ 58 src/ <span style="color:black"> 59 MyActivity.java </span> 60 res/ 61 drawable/ <span style="color:black"> 62 icon.png </span> 63 layout/ <span style="color:black"> 64 main.xml 65 info.xml</span> 66 values/ <span style="color:black"> 67 strings.xml </span> 68</pre> 69 70<p>As you can see in this example, the {@code res/} directory contains all the resources (in 71subdirectories): an image resource, two layout resources, and a string resource file. The resource 72directory names are important and are described in table 1.</p> 73 74<p class="table-caption" id="table1"><strong>Table 1.</strong> Resource directories 75supported inside project {@code res/} directory.</p> 76 77<table> 78 <tr> 79 <th scope="col">Directory</th> 80 <th scope="col">Resource Type</th> 81 </tr> 82 83 <tr> 84 <td><code>anim/</code></td> 85 <td>XML files that define tween animations. See <a 86href="animation-resource.html">Animation Resources</a>.</td> 87 </tr> 88 89 <tr> 90 <td><code>color/</code></td> 91 <td>XML files that define a state list of colors. See <a href="color-list-resource.html">Color 92State List Resource</a></td> 93 </tr> 94 95 <tr> 96 <td><code>drawable/</code></td> 97 <td><p>Bitmap files ({@code .png}, {@code .9.png}, {@code .jpg}, {@code .gif}) or XML files that 98are compiled into the following drawable resource subtypes:</p> 99 <ul> 100 <li>Bitmap files</li> 101 <li>Nine-Patches (re-sizable bitmaps)</li> 102 <li>State lists</li> 103 <li>Shapes</li> 104 <li>Animation drawables</li> 105 <li>Other drawables</li> 106 </ul> 107 <p>See <a href="drawable-resource.html">Drawable Resources</a>.</p> 108 </td> 109 </tr> 110 111 <tr> 112 <td><code>layout/</code></td> 113 <td>XML files that define a user interface layout. 114 See <a href="layout-resource.html">Layout Resource</a>.</td> 115 </tr> 116 117 <tr> 118 <td><code>menu/</code></td> 119 <td>XML files that define application menus, such as an Options Menu, Context Menu, or Sub 120Menu. See <a href="menu-resource.html">Menu Resource</a>.</td> 121 </tr> 122 123 <tr> 124 <td><code>raw/</code></td> 125 <td><p>Arbitrary files to save in their raw form. Files in here are not compressed by the 126system. To open these resources with a raw {@link java.io.InputStream}, call {@link 127android.content.res.Resources#openRawResource(int) 128Resources.openRawResource()} with the resource ID, which is {@code R.raw.<em>filename</em>}.</p> 129 <p>However, if you need access to original file names and file hierarchy, you might consider 130saving some resources in the {@code 131assets/} directory (instead of {@code res/raw/}). Files in {@code assets/} are not given a 132resource ID, so you can read them only using {@link android.content.res.AssetManager}.</p></td> 133 </tr> 134 135 <tr> 136 <td><code>values/</code></td> 137 <td><p>XML files that contain simple values, such as strings, integers, and colors.</p> 138 <p>Whereas XML resource files in other {@code res/} subdirectories define a single resource 139based on the XML filename, files in the {@code values/} directory describe multiple resources. 140For a file in this directory, each child of the {@code <resources>} element defines a single 141resource. For example, a {@code <string>} element creates an 142{@code R.string} resource and a {@code <color>} element creates an {@code R.color} 143resource.</p> 144 <p>Because each resource is defined with its own XML element, you can name the file 145whatever you want and place different resource types in one file. However, for clarity, you might 146want to place unique resource types in different files. For example, here are some filename 147conventions for resources you can create in this directory:</p> 148 <ul> 149 <li>arrays.xml for resource arrays (<a 150href="more-resources.html#TypedArray">typed arrays</a>).</li> 151 <li>colors.xml for <a 152href="more-resources.html#Color">color values</a></li> 153 <li>dimens.xml for <a 154href="more-resources.html#Dimension">dimension values</a>.</li> 155 <li>strings.xml for <a href="string-resource.html">string 156values</a>.</li> 157 <li>styles.xml for <a href="style-resource.html">styles</a>.</li> 158 </ul> 159 <p>See <a href="string-resource.html">String Resources</a>, 160 <a href="style-resource.html">Style Resource</a>, and 161 <a href="more-resources.html">More Resource Types</a>.</p> 162 </td> 163 </tr> 164 165 <tr> 166 <td><code>xml/</code></td> 167 <td>Arbitrary XML files that can be read at runtime by calling {@link 168android.content.res.Resources#getXml(int) Resources.getXML()}. Various XML configuration files 169must be saved here, such as a <a 170href="{@docRoot}guide/topics/search/searchable-config.html">searchable configuration</a>. 171<!-- or preferences configuration. --></td> 172 </tr> 173</table> 174 175<p class="caution"><strong>Caution:</strong> Never save resource files directly inside the 176{@code res/} directory—it will cause a compiler error.</p> 177 178<p>For more information about certain types of resources, see the <a 179href="available-resources.html">Resource Types</a> documentation.</p> 180 181<p>The resources that you save in the subdirectories defined in table 1 are your "default" 182resources. That is, these resources define the default design and content for your application. 183However, different types of Android-powered devices might call for different types of resources. 184For example, if a device has a larger than normal screen, then you should provide 185different layout resources that take advantage of the extra screen space. Or, if a device has a 186different language setting, then you should provide different string resources that translate the 187text in your user interface. To provide these different resources for different device 188configurations, you need to provide "alternative" resources, in addition to your default 189resources.</p> 190 191 192<h2 id="AlternativeResources">Providing Alternative Resources</h2> 193 194 195<div class="figure" style="width:421px"> 196<img src="{@docRoot}images/resources/resource_devices_diagram2.png" height="137" alt="" /> 197<p class="img-caption"> 198<strong>Figure 1.</strong> Two device configurations, one using alternative resources.</p> 199</div> 200 201<p>Almost every application should provide alternative resources to support specific device 202configurations. For instance, you should include alternative drawable resources for different 203screen densities and alternative string resources for different languages. At runtime, Android 204detects the current device configuration and loads the appropriate 205resources for your application.</p> 206 207<p>To specify configuration-specific alternatives for a set of resources:</p> 208<ol> 209 <li>Create a new directory in {@code res/} named in the form {@code 210<em><resources_name></em>-<em><config_qualifier></em>}. 211 <ul> 212 <li><em>{@code <resources_name>}</em> is the directory name of the corresponding default 213resources (defined in table 1).</li> 214 <li><em>{@code <config_qualifier>}</em> is a name that specifies a configuration 215for which these resources are to be used (defined in table 2).</li> 216 </ul> 217 <p>You can append more than one <em>{@code <config_qualifier>}</em>. Separate each 218one with a dash.</p> 219 </li> 220 <li>Save the respective alternative resources in this new directory. The resource files must be 221named exactly the same as the default resource files.</li> 222</ol> 223 224<p>For example, here are some default and alternative resources:</p> 225 226<pre class="classic no-pretty-print"> 227res/ 228 drawable/ <span style="color:black"> 229 icon.png 230 background.png </span> 231 drawable-hdpi/ <span style="color:black"> 232 icon.png 233 background.png </span> 234</pre> 235 236<p>The {@code hdpi} qualifier indicates that the resources in that directory are for devices with a 237high-density screen. The images in each of these drawable directories are sized for a specific 238screen density, but the filenames are exactly 239the same. This way, the resource ID that you use to reference the {@code icon.png} or {@code 240background.png} image is always the same, but Android selects the 241version of each resource that best matches the current device, by comparing the device 242configuration information with the qualifiers in the alternative resource directory name.</p> 243 244<p>Android supports several configuration qualifiers and you can 245add multiple qualifiers to one directory name, by separating each qualifier with a dash. Table 2 246lists the valid configuration qualifiers, in order of precedence—if you use multiple 247qualifiers for one resource directory, they must be added to the directory name in the order they 248are listed in the table.</p> 249 250<p class="note"><strong>Note:</strong> Some resource qualifiers were added after Android 1.0, so not 251all versions of Android support all the qualifiers listed in table 2. New qualifiers 252indicate the version in which they were added. To avoid any issues, always include a set of default 253resources for resources that your application uses. For more information, see the section about <a 254href="#Compatibility">Providing the Best Device Compatibility with Resources</a>.</p> 255 256<p class="table-caption" id="table2"><strong>Table 2.</strong> Alternative resource qualifier 257names.</p> 258<table> 259 <tr> 260 <th>Qualifier</th> 261 <th>Values</th> 262 <th>Description</th> 263 </tr> 264 <tr id="MccQualifier"> 265 <td>MCC and MNC</td> 266 <td>Examples:<br/> 267 <code>mcc310</code><br/> 268 <code><nobr>mcc310-mnc004</nobr></code><br/> 269 <code>mcc208-mnc00</code><br/> 270 etc. 271 </td> 272 <td> 273 <p>The mobile country code (MCC), optionally followed by mobile network code (MNC) 274 from the SIM card in the device. For example, <code>mcc310</code> is U.S. on any carrier, 275 <code>mcc310-mnc004</code> is U.S. on Verizon, and <code>mcc208-mnc00</code> is France on 276 Orange.</p> 277 <p>If the device uses a radio connection (GSM phone), the MCC comes 278 from the SIM, and the MNC comes from the network to which the 279 device is connected.</p> 280 <p>You can also use the MCC alone (for example, to include country-specific legal 281resources in your application). If you need to specify based on the language only, then use the 282<em>language and region</em> qualifier instead (discussed next). If you decide to use the MCC and 283MNC qualifier, you should do so with care and test that it works as expected.</p> 284 <p>Also see the configuration fields {@link 285android.content.res.Configuration#mcc}, and {@link 286android.content.res.Configuration#mnc}, which indicate the current mobile country code 287and mobile network code, respectively.</p> 288 </td> 289 </tr> 290 <tr id="LocaleQualifier"> 291 <td>Language and region</td> 292 <td>Examples:<br/> 293 <code>en</code><br/> 294 <code>fr</code><br/> 295 <code>en-rUS</code><br/> 296 <code>fr-rFR</code><br/> 297 <code>fr-rCA</code><br/> 298 etc. 299 </td> 300 <td><p>The language is defined by a two-letter <a 301href="http://www.loc.gov/standards/iso639-2/php/code_list.php">ISO 302 639-1</a> language code, optionally followed by a two letter 303 <a 304href="http://www.iso.org/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html">ISO 305 3166-1-alpha-2</a> region code (preceded by lowercase "{@code r}"). 306 </p><p> 307 The codes are <em>not</em> case-sensitive; the {@code r} prefix is used to 308 distinguish the region portion. 309 You cannot specify a region alone.</p> 310 <p>This can change during the life 311of your application if the user changes his or her language in the system settings. See <a 312href="runtime-changes.html">Handling Runtime Changes</a> for information about 313how this can affect your application during runtime.</p> 314 <p>See <a href="localization.html">Localization</a> for a complete guide to localizing 315your application for other languages.</p> 316 <p>Also see the {@link android.content.res.Configuration#locale} configuration field, which 317indicates the current locale.</p> 318 </td> 319 </tr> 320 <tr id="ScreenSizeQualifier"> 321 <td>Screen size</td> 322 <td> 323 <code>small</code><br/> 324 <code>normal</code><br/> 325 <code>large</code> 326 </td> 327 <td> 328 <ul class="nolist"> 329 <li>{@code small}: Screens based on the space available on a 330 low-density QVGA screen. Considering a portrait HVGA display, this has 331 the same available width but less height—it is 3:4 vs. HVGA's 332 2:3 aspect ratio. Examples are QVGA low density and VGA high 333 density.</li> 334 <li>{@code normal}: Screens based on the traditional 335 medium-density HVGA screen. A screen is considered to be normal if it is 336 at least this size (independent of density) and not larger. Examples 337 of such screens a WQVGA low density, HVGA medium density, WVGA 338 high density.</li> 339 <li>{@code large}: Screens based on the space available on a 340 medium-density VGA screen. Such a screen has significantly more 341 available space in both width and height than an HVGA display. 342 Examples are VGA and WVGA medium density screens.</li> 343 </ul> 344 <p><em>Added in API Level 4.</em></p> 345 <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 346Screens</a> for more information.</p> 347 <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field, 348which indicates whether the screen is small, normal, 349or large.</p> 350 </td> 351 </tr> 352 <tr id="ScreenLongQualifier"> 353 <td>Wider/taller screens</td> 354 <td> 355 <code>long</code><br/> 356 <code>notlong</code> 357 </td> 358 <td> 359 <ul class="nolist"> 360 <li>{@code long}: Long screens, such as WQVGA, WVGA, FWVGA</li> 361 <li>{@code notlong}: Not long screens, such as QVGA, HVGA, and VGA</li> 362 </ul> 363 <p><em>Added in API Level 4.</em></p> 364 <p>This is based purely on the aspect ratio of the screen (a "long" screen is wider). This 365is not related to the screen orientation.</p> 366 <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field, 367which indicates whether the screen is long.</p> 368 </td> 369 </tr> 370 <tr id="OrientationQualifier"> 371 <td>Screen orientation</td> 372 <td> 373 <code>port</code><br/> 374 <code>land</code> <!-- <br/> 375 <code>square</code> --> 376 </td> 377 <td> 378 <ul class="nolist"> 379 <li>{@code port}: Device is in portrait orientation (vertical)</li> 380 <li>{@code land}: Device is in landscape orientation (horizontal)</li> 381 <!-- Square mode is currently not used. --> 382 </ul> 383 <p>This can change during the life of your application if the user rotates the 384screen. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about 385how this affects your application during runtime.</p> 386 <p>Also see the {@link android.content.res.Configuration#orientation} configuration field, 387which indicates the current device orientation.</p> 388 </td> 389 </tr> 390 <tr id="DockQualifier"> 391 <td>Dock mode</td> 392 <td> 393 <code>car</code><br/> 394 <code>desk</code> 395 </td> 396 <td> 397 <ul class="nolist"> 398 <li>{@code car}: Device is in a car dock</li> 399 <li>{@code desk}: Device is in a desk dock</li> 400 </ul> 401 <p><em>Added in API Level 8.</em></p> 402 <p>This can change during the life of your application if the user places the device in a 403dock. You can enable or disable this mode using {@link 404android.app.UiModeManager}. See <a href="runtime-changes.html">Handling Runtime Changes</a> for 405information about how this affects your application during runtime.</p> 406 </td> 407 </tr> 408 <tr id="NightQualifier"> 409 <td>Night mode</td> 410 <td> 411 <code>night</code><br/> 412 <code>notnight</code> 413 </td> 414 <td> 415 <ul class="nolist"> 416 <li>{@code night}: Night time</li> 417 <li>{@code notnight}: Day time</li> 418 </ul> 419 <p><em>Added in API Level 8.</em></p> 420 <p>This can change during the life of your application if night mode is left in 421auto mode (default), in which case the mode changes based on the time of day. You can enable 422or disable this mode using {@link android.app.UiModeManager}. See <a 423href="runtime-changes.html">Handling Runtime Changes</a> for information about how this affects your 424application during runtime.</p> 425 </td> 426 </tr> 427 <tr id="DensityQualifier"> 428 <td>Screen pixel density (dpi)</td> 429 <td> 430 <code>ldpi</code><br/> 431 <code>mdpi</code><br/> 432 <code>hdpi</code><br/> 433 <code>nodpi</code> 434 </td> 435 <td> 436 <ul class="nolist"> 437 <li>{@code ldpi}: Low-density screens; approximately 120dpi.</li> 438 <li>{@code mdpi}: Medium-density (on traditional HVGA) screens; approximately 439160dpi.</li> 440 <li>{@code hdpi}: High-density screens; approximately 240dpi.</li> 441 <li>{@code nodpi}: This can be used for bitmap resources that you do not want to be scaled 442to match the device density.</li> 443 </ul> 444 <p><em>Added in API Level 4.</em></p> 445 <p>There is thus a 4:3 scaling factor between each density, so a 9x9 bitmap 446 in ldpi is 12x12 in mdpi and 16x16 in hdpi.</p> 447 <p>When Android selects which resource files to use, 448 it handles screen density differently than the other qualifiers. 449 In step 1 of <a href="#BestMatch">How Android finds the best 450 matching directory</a> (below), screen density is always considered to 451 be a match. In step 4, if the qualifier being considered is screen 452 density, Android selects the best final match at that point, 453 without any need to move on to step 5. 454 </p> 455 <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 456Screens</a> for more information about how to handle screen sizes and how Android might scale 457your bitmaps.</p> 458 </td> 459 </tr> 460 <tr id="TouchscreenQualifier"> 461 <td>Touchscreen type</td> 462 <td> 463 <code>notouch</code><br/> 464 <code>stylus</code><br/> 465 <code>finger</code> 466 </td> 467 <td> 468 <ul class="nolist"> 469 <li>{@code notouch}: Device does not have a touchscreen.</li> 470 <li>{@code stylus}: Device has a resistive touchscreen that's suited for use with a 471stylus.</li> 472 <li>{@code finger}: Device has a touchscreen.</li> 473 </ul> 474 <p>Also see the {@link android.content.res.Configuration#touchscreen} configuration field, 475which indicates the type of touchscreen on the device.</p> 476 </td> 477 </tr> 478 <tr id="KeyboardAvailQualifier"> 479 <td>Keyboard availability</td> 480 <td> 481 <code>keysexposed</code><br/> 482 <code>keyssoft</code> 483 </td> 484 <td> 485 <ul class="nolist"> 486 <li>{@code keysexposed}: Device has a keyboard available. If the device has a 487software keyboard enabled (which is likely), this may be used even when the hardware keyboard is 488<em>not</em> exposed to the user, even if the device has no hardware keyboard. If no software 489keyboard is provided or it's disabled, then this is only used when a hardware keyboard is 490exposed.</li> 491 <li>{@code keyshidden}: Device has a hardware keyboard available but it is 492hidden <em>and</em> the device does <em>not</em> have a software keyboard enabled.</li> 493 <li>{@code keyssoft}: Device has a software keyboard enabled, whether it's 494visible or not.</li> 495 </ul> 496 <p>If you provide <code>keysexposed</code> resources, but not <code>keyssoft</code> 497resources, the system uses the <code>keysexposed</code> resources regardless of whether a 498keyboard is visible, as long as the system has a software keyboard enabled.</p> 499 <p>This can change during the life of your application if the user opens a hardware 500keyboard. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about how 501this affects your application during runtime.</p> 502 <p>Also see the configuration fields {@link 503android.content.res.Configuration#hardKeyboardHidden} and {@link 504android.content.res.Configuration#keyboardHidden}, which indicate the visibility of a hardware 505keyboard and and the visibility of any kind of keyboard (including software), respectively.</p> 506 </td> 507 </tr> 508 <tr id="ImeQualifier"> 509 <td>Primary text input method</td> 510 <td> 511 <code>nokeys</code><br/> 512 <code>qwerty</code><br/> 513 <code>12key</code> 514 </td> 515 <td> 516 <ul class="nolist"> 517 <li>{@code nokeys}: Device has no hardware keys for text input.</li> 518 <li>{@code qwerty}: Device has a hardware qwerty keyboard, whether it's visible to the 519user 520or not.</li> 521 <li>{@code 12key}: Device has a hardware 12-key keyboard, whether it's visible to the user 522or not.</li> 523 </ul> 524 <p>Also see the {@link android.content.res.Configuration#keyboard} configuration field, 525which indicates the primary text input method available.</p> 526 </td> 527 </tr> 528 <tr id="NavAvailQualifier"> 529 <td>Navigation key availability</td> 530 <td> 531 <code>navexposed</code><br/> 532 <code>navhidden</code> 533 </td> 534 <td> 535 <ul class="nolist"> 536 <li>{@code navexposed}: Navigation keys are available to the user.</li> 537 <li>{@code navhidden}: Navigation keys are not available (such as behind a closed 538lid).</li> 539 </ul> 540 <p>This can change during the life of your application if the user reveals the navigation 541keys. See <a href="runtime-changes.html">Handling Runtime Changes</a> for 542information about how this affects your application during runtime.</p> 543 <p>Also see the {@link android.content.res.Configuration#navigationHidden} configuration 544field, which indicates whether navigation keys are hidden.</p> 545 </td> 546 </tr> 547 <tr id="TouchQualifier"> 548 <td>Primary non-touch navigation method</td> 549 <td> 550 <code>nonav</code><br/> 551 <code>dpad</code><br/> 552 <code>trackball</code><br/> 553 <code>wheel</code> 554 </td> 555 <td> 556 <ul class="nolist"> 557 <li>{@code nonav}: Device has no navigation facility other than using the 558touchscreen.</li> 559 <li>{@code dpad}: Device has a directional-pad (d-pad) for navigation.</li> 560 <li>{@code trackball}: Device has a trackball for navigation.</li> 561 <li>{@code wheel}: Device has a directional wheel(s) for navigation (uncommon).</li> 562 </ul> 563 <p>Also see the {@link android.content.res.Configuration#navigation} configuration field, 564which indicates the type of navigation method available.</p> 565 </td> 566 </tr> 567<!-- DEPRECATED 568 <tr> 569 <td>Screen dimensions</td> 570 <td>Examples:<br/> 571 <code>320x240</code><br/> 572 <code>640x480</code><br/> 573 etc. 574 </td> 575 <td> 576 <p>The larger dimension must be specified first. <strong>This configuration is deprecated 577and should not be used</strong>. Instead use "screen size," "wider/taller screens," and "screen 578orientation" described above.</p> 579 </td> 580 </tr> 581--> 582 <tr id="VersionQualifier"> 583 <td>System Version (API Level)</td> 584 <td>Examples:<br/> 585 <code>v3</code><br/> 586 <code>v4</code><br/> 587 <code>v7</code><br/> 588 etc.</td> 589 <td> 590 <p>The API Level supported by the device. For example, <code>v1</code> for API Level 5911 (devices with Android 1.0 or higher) and <code>v4</code> for API Level 4 (devices with Android 5921.6 or higher). See the <a 593href="{@docRoot}guide/appendix/api-levels.html">Android API Levels</a> document for more information 594about these values.</p> 595 <p class="caution"><strong>Caution:</strong> Android 1.5 and 1.6 only match resources 596with this qualifier when it exactly matches the system version. See the section below about <a 597href="#KnownIssues">Known Issues</a> for more information.</p> 598 </td> 599 </tr> 600</table> 601 602 603<h3 id="QualifierRules">Qualifier name rules</h3> 604 605<p>Here are some rules about using resource qualifier names:</p> 606 607<ul> 608 <li>You can specify multiple qualifiers for a single set of resources, separated by dashes. For 609example, <code>drawable-en-rUS-land</code> applies to US-English devices in landscape 610orientation.</li> 611 <li>The qualifiers must be in the order listed in <a href="#table2">table 2</a>. For 612example: 613 <ul> 614 <li>Wrong: <code>drawable-hdpi-port/</code></li> 615 <li>Correct: <code>drawable-port-hdpi/</code></li> 616 </ul> 617 </li> 618 <li>Alternative resource directories cannot be nested. For example, you cannot have 619<code>res/drawable/drawable-en/</code>.</li> 620 <li>Values are case-insensitive. The resource compiler converts directory names 621 to lower case before processing to avoid problems on case-insensitive 622 file systems. Any capitalization in the names is only to benefit readability.</li> 623 <li>Only one value for each qualifier type is supported. For example, if you want to use 624the same drawable files for Spain and France, you <em>cannot</em> have a directory named 625<code>drawable-rES-rFR/</code>. Instead you need two resource directories, such as 626<code>drawable-rES/</code> and <code>drawable-rFR/</code>, which contain the appropriate files. 627However, you are not required to actually duplicate the same files in both locations. Instead, you 628can create an alias to a resource. See <a href="#AliasResources">Creating 629alias resources</a> below.</li> 630</ul> 631 632<p>After you save alternative resources into directories named with 633these qualifiers, Android automatically applies the resources in your application based on the 634current device configuration. Each time a resource is requested, Android checks for alternative 635resource directories that contain the requested resource file, then <a href="#BestMatch">finds the 636best-matching resource</a> (discussed below).</p> 637 638 639 640<h3 id="AliasResources">Creating alias resources</h3> 641 642<p>When you have a resource that you'd like to use for more than one device 643configuration (but not for all configurations), you do not need to put the same resource in 644each alternative resource directory. Instead, you can (in some cases) create an alternative 645resource that acts as an alias for a resource saved in your default resource directory.</p> 646 647<p class="note"><strong>Note:</strong> Not all resources offer a mechanism by which you can 648create an alias to another resource. In particular, animation, menu, raw, and other unspecified 649resources in the {@code xml/} directory do not offer this feature.</p> 650 651<p>For example, imagine you have an application icon, {@code icon.png}, and need unique version of 652it for different locales. However, two locales, English-Canadian and French-Canadian, need to 653use the same version. You might assume that you need to copy the same image 654into the resource directory for both English-Canadian and French-Canadian, but it's 655not true. Instead, you can save the image that's used for both as {@code icon_ca.png} (any 656name other than {@code icon.png}) and put 657it in the default {@code res/drawable/} directory. Then create an {@code icon.xml} file in {@code 658res/drawable-en-rCA/} and {@code res/drawable-fr-rCA/} that refers to the {@code icon_ca.png} 659resource using the {@code <bitmap>} element. This allows you to store just one version of the 660PNG file and two small XML files that point to it. (An example XML file is shown below.)</p> 661 662 663<h4>Drawable</h4> 664 665<p>To create an alias to an existing drawable, use the {@code <bitmap>} element. 666For example:</p> 667 668<pre> 669<?xml version="1.0" encoding="utf-8"?> 670<bitmap xmlns:android="http://schemas.android.com/apk/res/android" 671 android:src="@drawable/icon_ca" /> 672</pre> 673 674<p>If you save this file as {@code icon.xml} (in an alternative resource directory, such as 675{@code res/drawable-en-rCA/}), it is compiled into a resource that you 676can reference as {@code R.drawable.icon}, but is actually an alias for the {@code 677R.drawable.icon_ca} resource (which is saved in {@code res/drawable/}).</p> 678 679 680<h4>Layout</h4> 681 682<p>To create an alias to an existing layout, use the {@code <include>} 683element, wrapped in a {@code <merge>}. For example:</p> 684 685<pre> 686<?xml version="1.0" encoding="utf-8"?> 687<merge> 688 <include layout="@layout/main_ltr"/> 689</merge> 690</pre> 691 692<p>If you save this file as {@code main.xml}, it is compiled into a resource you can reference 693as {@code R.layout.main}, but is actually an alias for the {@code R.layout.main_ltr} 694resource.</p> 695 696 697<h4>Strings and other simple values</h4> 698 699<p>To create an alias to an existing string, simply use the resource ID of the desired 700string as the value for the new string. For example:</p> 701 702<pre> 703<?xml version="1.0" encoding="utf-8"?> 704<resources> 705 <string name="hello">Hello</string> 706 <string name="hi">@string/hello</string> 707</resources> 708</pre> 709 710<p>The {@code R.string.hi} resource is now an alias for the {@code R.string.hello}.</p> 711 712<p> <a href="{@docRoot}guide/topics/resources/more-resources.html">Other simple values</a> work the 713same way. For example, a color:</p> 714 715<pre> 716<?xml version="1.0" encoding="utf-8"?> 717<resources> 718 <color name="yellow">#f00</color> 719 <color name="highlight">@color/red</color> 720</resources> 721</pre> 722 723 724 725 726 727<h2 id="Compatibility">Providing the Best Device Compatibility with Resources</h2> 728 729<p>In order for your application to support multiple device configurations, it's very important that 730you always provide default resources for each type of resource that your application uses.</p> 731 732<p>For example, if your application supports several languages, always include a {@code 733values/} directory (in which your strings are saved) <em>without</em> a <a 734href="#LocalQualifier">language and region qualifier</a>. If you instead put all your string files 735in directories that have a language and region qualifier, then your application will crash when run 736on a device set to a language that your strings do not support. But, as long as you provide default 737{@code values/} resources, then your application will run properly (even if the user doesn't 738understand that language—it's better than crashing).</p> 739 740<p>Likewise, if you provide different layout resources based on the screen orientation, you should 741pick one orientation as your default. For example, instead of providing layout resources in {@code 742layout-land/} for landscape and {@code layout-port/} for portrait, leave one as the default, such as 743{@code layout/} for landscape and {@code layout-port/} for portrait.</p> 744 745<p>Providing default resources is important not only because your application might run on a 746configuration you had not anticipated, but also because new versions of Android sometimes add 747resource qualifiers that older versions do not support. If you use a new resource qualifier, 748but maintain code compatibility with older versions of Android, then when an older version of 749Android runs your application, it will crash if you do not provide default resources, because it 750cannot use the resources named with the new qualifier. For example, if your <a 751href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code 752minSdkVersion}</a> is set to 4, and you qualify all of your drawable resources using <a 753href="NightQualifier">night mode</a> ({@code night} or {@code notnight}, which were added in API 754Level 8), then an API Level 4 device cannot access your drawable resources and will crash. In this 755case, you probably want {@code notnight} to be your default resources, so you should exclude that 756qualifier so your drawable resources are in either {@code drawable/} or {@code drawable-night/}.</p> 757 758<p>The bottom line is: For every type of resource your application uses, 759provide a set of default resources that allow your application to perform well, then create 760variations of those resources for specific device configurations.</p> 761 762<p>There is one exception to this rule: If your application's <a 763href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is 4 or 764greater, you <em>do not</em> need default drawable resources when you provide alternative drawable 765resources with the <a href="#DensityQualifier">screen density</a> qualifier. Even without default 766drawable resources, Android can find the best match among the alternative screen densities and scale 767the bitmaps as necessary. However, for the best experience on all types of devices, you should 768provide alternative drawables for all three types of density. (If your <a 769href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is 770<em>less than</em> 4, see the section below about <a href="#KnownIssues">known issues</a> for 771information about how to support multiple screen densities.)</p> 772 773 774 775 776<h2 id="BestMatch">How Android Finds the Best-matching Resource</h2> 777 778<p>When you request a resource for which you provide alternatives, Android selects which 779alternative resource to use at runtime, depending on the current device configuration. To 780demonstrate how Android selects an alternative resource, assume the following drawable directories 781each contain different versions of the same images:</p> 782 783<pre class="classic no-pretty-print"> 784drawable/ 785drawable-en/ 786drawable-fr-rCA/ 787drawable-en-port/ 788drawable-en-notouch-12key/ 789drawable-port-ldpi/ 790drawable-port-notouch-12key/ 791</pre> 792 793<p>And assume the following is the device configuration:</p> 794 795<p style="margin-left:1em;"> 796Locale = <code>en-GB</code> <br/> 797Screen orientation = <code>port</code> <br/> 798Screen pixel density = <code>hdpi</code> <br/> 799Touchscreen type = <code>notouch</code> <br/> 800Primary text input method = <code>12key</code> 801</p> 802 803<p>By comparing the device configuration to the available alternative resources, Android selects 804drawables from {@code drawable-en-port}. It arrives at this decision using the following logic:</p> 805 806 807<div class="figure" style="width:280px"> 808<img src="{@docRoot}images/resources/res-selection-flowchart.png" alt="" height="590" /> 809<p class="img-caption"><strong>Figure 2.</strong> Flowchart of how Android finds the 810best-matching resource.</p> 811</div> 812 813 814<ol> 815 <li>Eliminate resource files that contradict the device configuration. 816 <p>The <code>drawable-fr-rCA/</code> directory is eliminated, because it 817contradicts the <code>en-GB</code> locale.</p> 818<pre class="classic no-pretty-print"> 819drawable/ 820drawable-en/ 821<strike>drawable-fr-rCA/</strike> 822drawable-en-port/ 823drawable-en-notouch-12key/ 824drawable-port-ldpi/ 825drawable-port-notouch-12key/ 826</pre> 827<p class="note"><strong>Exception:</strong> Screen pixel density is the one qualifier that is not 828eliminated due to a contradiction. Even though the screen density of the device is mdpi, 829<code>drawable-port-ldpi/</code> is not eliminated because every screen density is 830considered to be a match at this point. More information is available in the <a 831href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 832Screens</a> document.</p></li> 833 834 <li>Pick the (next) highest-precedence qualifier in the list (<a href="#table2">table 2</a>). 835(Start with MCC, then move down.) </li> 836 <li>Do any of the resource directories include this qualifier? </li> 837 <ul> 838 <li>If No, return to step 2 and look at the next qualifier. (In the example, 839 the answer is "no" until the language qualifier is reached.)</li> 840 <li>If Yes, continue to step 4.</li> 841 </ul> 842 </li> 843 844 <li>Eliminate resource directories that do not include this qualifier. In the example, the system 845eliminates all the directories that do not include a language qualifier:</li> 846<pre class="classic no-pretty-print"> 847<strike>drawable/</strike> 848drawable-en/ 849drawable-en-port/ 850drawable-en-notouch-12key/ 851<strike>drawable-port-ldpi/</strike> 852<strike>drawable-port-notouch-12key/</strike> 853</pre> 854<p class="note"><strong>Exception:</strong> If the qualifier in question is screen pixel density, 855Android 856selects the option that most closely matches the device, and the selection process is complete. 857In general, Android prefers scaling down a larger original image to scaling up a smaller 858original image. See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 859Screens</a>.</p> 860 </li> 861 862 <li>Go back and repeat steps 2, 3, and 4 until only one directory remains. In the example, screen 863orientation is the next qualifier for which there are any matches. 864So, resources that do not specify a screen orientation are eliminated: 865<pre class="classic no-pretty-print"> 866<strike>drawable-en/</strike> 867drawable-en-port/ 868<strike>drawable-en-notouch-12key/</strike> 869</pre> 870<p>The remaining directory is {@code drawable-en-port}.</p> 871 </li> 872</ol> 873 874<p>Though this procedure is executed for each resource requested, the system further optimizes 875some aspects. One such optimization is that once the device configuration is known, it might 876eliminate alternative resources that can never match. For example, if the configuration 877language is English ("en"), then any resource directory that has a language qualifier set to 878something other than English is never included in the pool of resources checked (though a 879resource directory <em>without</em> the language qualifier is still included).</p> 880 881<p class="note"><strong>Note:</strong> The <em>precedence</em> of the qualifier (in <a 882href="#table2">table 2</a>) is more important 883than the number of qualifiers that exactly match the device. For example, in step 4 above, the last 884choice on the list includes three qualifiers that exactly match the device (orientation, touchscreen 885type, and input method), while <code>drawable-en</code> has only one parameter that matches 886(language). However, language has a higher precedence than these other qualifiers, so 887<code>drawable-port-notouch-12key</code> is out.</p> 888 889<p>To learn more about how to use resources in your application, continue to <a 890href="accessing-resources.html">Accessing Resources</a>.</p> 891 892 893 894 895<h2 id="KnownIssues">Known Issues</h2> 896 897<p>The following are known issues in terms of how Android finds the best-matching resource on 898certain versions of Android.</p> 899 900<h3>Android 1.5 (and lower)</h3> 901 902<h4>Density and screen size qualifiers are not supported</h4> 903 904<p>Android 1.5 (and lower) does not support the following resource qualifers:</p> 905<dl> 906 <dt><a href="#DensityQualifier">Density</a></dt> 907 <dd>{@code ldpi}, {@code mdpi}, {@code ldpi}, and {@code nodpi}</dd> 908 <dt><a href="#ScreenSizeQualifier">Screen size</a></dt> 909 <dd>{@code small}, {@code normal}, and {@code large}</dd> 910 <dt><a href="#ScreenLongQualifier">Screen length</a></dt> 911 <dd>{@code long} and {@code notlong}</dd> 912</dl> 913 914<p>These resource qualifiers were introduced in Android 1.6, so Android 1.5 (API Level 3) and lower 915does not support them. If your application supports Android 1.5 and includes drawable resources for 916each density type ({@code drawable-ldpi/}, {@code drawable-mdpi/}, and {@code drawable-ldpi/}), then 917an Android 1.5 device might use any one of them, because it doesn't support the density qualifier, 918will ignore it, and will use which ever otherwise-matching drawable resource it finds first. This 919caveat applies the same to screen size and screen length resources.<p> 920 921<p><b>The fix:</b> Ensure that your <a href="{@docRoot}sdk/tools-notes.html">SDK Tools</a> version 922is r6 or greater and provide default drawable resources. For example, to support Android 1.5 923while providing resources for all screen densities, include a set of drawable resources that does 924not use the screen density qualifier. In fact, because all Android 1.5 devices have a medium-density 925screen, you can remove the {@code mdpi} qualifer and put all medium density images in {@code 926drawable/} (instead of {@code drawable-mdpi/}). For the screen size, put your {@code normal} size 927resources in the default resource directory, and for the screen length, put your {@code notlong} 928resources in the default resource directory (because all Android 1.5 devices have medium-density, 929normal, not-long screens).</p> 930 931<p>You need SDK Tools, Revision 6 (or greater), because it includes a new packaging tool that 932automatically applies an appropriate <a href="#VersionQualifier">version qualifier</a> to any 933resource directory named with a qualifier that did not exist in Android 1.0. For example, because 934the density qualifier was introduced in Android 1.6 (API Level 4), when the packaging tool 935encounters a resource directory using the density qualifier, it adds {@code v4} to the directory 936name to ensure that older versions do not use those resources (only API Level 4 and higher support 937that qualifier). Thus, by putting your medium-density resources in a directory <em>without</em> the 938{@code mdpi} qualifier, they are still accessible by Android 1.5, and any device that supports the 939density qualifer and has a medium-density screen also uses these resources because they are the best 940match for the device (instead of using the {@code ldpi} or {@code hdpi} resources).</p> 941 942<p class="note"><strong>Note:</strong> Later versions of Android, such as API Level 8, 943introduce other resource qualifiers that older version do not support. To provide the best 944compatibility, you should always include a set of default resources for each type of resource 945that your application uses. See the section about <a href="#Compatibility">Providing the Best Device 946Compatibility with Resources</a> for more information.</p> 947 948 949 950<h3>Android 1.5 and 1.6</h3> 951 952<h4>Version qualifier performs exact match, instead of best match</h4> 953 954<p>The correct behavior is for the system to match resources marked with a <a 955href="#VersionQualifier">version qualifier</a> equal 956to or less than the system version on the device, but on Android 1.5 and 1.6, (API Level 3 and 4), 957there is a bug that causes the system to match resources marked with the version qualifier 958only when it exactly matches the version on the device.</p> 959 960<p><b>The fix:</b> To provide version-specific resources, abide by this behavior. However, because 961this bug is fixed in versions of Android available after 1.6, if 962you need to differentiate resources between Android 1.5, 1.6, and later versions, then you only need 963to apply the version qualifier to the 1.6 resources and one to match all later versions. Thus, this 964is effectively a non-issue.</p> 965 966<p>For example, if you want drawable resources that are different on each Android 1.5, 1.6, 967and 2.0.1 (and later), create three drawable directories: {@code drawable/} (for 1.5 and lower), 968{@code drawable-v4} (for 1.6), and {@code drawable-v6} (for 2.0.1 and later—version 2.0, v5, 969is no longer available).</p> 970 971 972