providing-resources.jd revision 821ca51857f4d21b231cd9ead786227b771fe759
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 13device configurations</li> 14 </ul> 15 <h2>In this document</h2> 16 <ol> 17 <li><a href="#ResourceTypes">Grouping Resource Types</a></li> 18 <li><a href="#AlternativeResources">Providing Alternative Resources</a> 19 <ol> 20 <li><a href="#QualifierRules">Qualifier name rules</a></li> 21 <li><a href="#AliasResources">Creating alias resources</a></li> 22 </ol> 23 </li> 24 <li><a href="#Compatibility">Providing the Best Device Compatibility with Resources</a> 25 <ol> 26 <li><a href="#ScreenCompatibility">Providing screen resource compatibility for Android 271.5</a></li> 28 </ol> 29 </li> 30 <li><a href="#BestMatch">How Android Finds the Best-matching Resource</a></li> 31 <li><a href="#KnownIssues">Known Issues</a></li> 32 </ol> 33 34 <h2>See also</h2> 35 <ol> 36 <li><a href="accessing-resources.html">Accessing Resources</a></li> 37 <li><a href="available-resources.html">Resource Types</a></li> 38 <li><a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 39Screens</a></li> 40 </ol> 41</div> 42</div> 43 44<p>You should always externalize application resources such as images and strings from your 45code, so that you can maintain them independently. You should also provide alternative resources for 46specific device configurations, by grouping them in specially-named resource directories. At 47runtime, Android uses uses the appropriate resource based on the current configuration. For 48example, you might want to provide a different UI layout depending on the screen size or different 49strings depending on the language setting.</p> 50 51<p>Once you externalize your application resources, you can access them 52using resource IDs that are generated in your project's {@code R} class. How to use 53resources in your application is discussed in <a href="accessing-resources.html">Accessing 54Resources</a>. This document shows you how to group your resources in your Android project and 55provide alternative resources for specific device configurations.</p> 56 57 58<h2 id="ResourceTypes">Grouping Resource Types</h2> 59 60<p>You should place each type of resource in a specific subdirectory of your project's 61{@code res/} directory. For example, here's the file hierarchy for a simple project:</p> 62 63<pre class="classic no-pretty-print"> 64MyProject/ 65 src/ <span style="color:black"> 66 MyActivity.java </span> 67 res/ 68 drawable/ <span style="color:black"> 69 icon.png </span> 70 layout/ <span style="color:black"> 71 main.xml 72 info.xml</span> 73 values/ <span style="color:black"> 74 strings.xml </span> 75</pre> 76 77<p>As you can see in this example, the {@code res/} directory contains all the resources (in 78subdirectories): an image resource, two layout resources, and a string resource file. The resource 79directory names are important and are described in table 1.</p> 80 81<p class="table-caption" id="table1"><strong>Table 1.</strong> Resource directories 82supported inside project {@code res/} directory.</p> 83 84<table> 85 <tr> 86 <th scope="col">Directory</th> 87 <th scope="col">Resource Type</th> 88 </tr> 89 90 <tr> 91 <td><code>anim/</code></td> 92 <td>XML files that define tween animations. See <a 93href="animation-resource.html">Animation Resources</a>.</td> 94 </tr> 95 96 <tr> 97 <td><code>color/</code></td> 98 <td>XML files that define a state list of colors. See <a href="color-list-resource.html">Color 99State List Resource</a></td> 100 </tr> 101 102 <tr> 103 <td><code>drawable/</code></td> 104 <td><p>Bitmap files ({@code .png}, {@code .9.png}, {@code .jpg}, {@code .gif}) or XML files that 105are compiled into the following drawable resource subtypes:</p> 106 <ul> 107 <li>Bitmap files</li> 108 <li>Nine-Patches (re-sizable bitmaps)</li> 109 <li>State lists</li> 110 <li>Shapes</li> 111 <li>Animation drawables</li> 112 <li>Other drawables</li> 113 </ul> 114 <p>See <a href="drawable-resource.html">Drawable Resources</a>.</p> 115 </td> 116 </tr> 117 118 <tr> 119 <td><code>layout/</code></td> 120 <td>XML files that define a user interface layout. 121 See <a href="layout-resource.html">Layout Resource</a>.</td> 122 </tr> 123 124 <tr> 125 <td><code>menu/</code></td> 126 <td>XML files that define application menus, such as an Options Menu, Context Menu, or Sub 127Menu. See <a href="menu-resource.html">Menu Resource</a>.</td> 128 </tr> 129 130 <tr> 131 <td><code>raw/</code></td> 132 <td><p>Arbitrary files to save in their raw form. Files in here are not compressed by the 133system. To open these resources with a raw {@link java.io.InputStream}, call {@link 134android.content.res.Resources#openRawResource(int) 135Resources.openRawResource()} with the resource ID, which is {@code R.raw.<em>filename</em>}.</p> 136 <p>However, if you need access to original file names and file hierarchy, you might consider 137saving some resources in the {@code 138assets/} directory (instead of {@code res/raw/}). Files in {@code assets/} are not given a 139resource ID, so you can read them only using {@link android.content.res.AssetManager}.</p></td> 140 </tr> 141 142 <tr> 143 <td><code>values/</code></td> 144 <td><p>XML files that contain simple values, such as strings, integers, and colors.</p> 145 <p>Whereas XML resource files in other {@code res/} subdirectories define a single resource 146based on the XML filename, files in the {@code values/} directory describe multiple resources. 147For a file in this directory, each child of the {@code <resources>} element defines a single 148resource. For example, a {@code <string>} element creates an 149{@code R.string} resource and a {@code <color>} element creates an {@code R.color} 150resource.</p> 151 <p>Because each resource is defined with its own XML element, you can name the file 152whatever you want and place different resource types in one file. However, for clarity, you might 153want to place unique resource types in different files. For example, here are some filename 154conventions for resources you can create in this directory:</p> 155 <ul> 156 <li>arrays.xml for resource arrays (<a 157href="more-resources.html#TypedArray">typed arrays</a>).</li> 158 <li>colors.xml for <a 159href="more-resources.html#Color">color values</a></li> 160 <li>dimens.xml for <a 161href="more-resources.html#Dimension">dimension values</a>.</li> 162 <li>strings.xml for <a href="string-resource.html">string 163values</a>.</li> 164 <li>styles.xml for <a href="style-resource.html">styles</a>.</li> 165 </ul> 166 <p>See <a href="string-resource.html">String Resources</a>, 167 <a href="style-resource.html">Style Resource</a>, and 168 <a href="more-resources.html">More Resource Types</a>.</p> 169 </td> 170 </tr> 171 172 <tr> 173 <td><code>xml/</code></td> 174 <td>Arbitrary XML files that can be read at runtime by calling {@link 175android.content.res.Resources#getXml(int) Resources.getXML()}. Various XML configuration files 176must be saved here, such as a <a 177href="{@docRoot}guide/topics/search/searchable-config.html">searchable configuration</a>. 178<!-- or preferences configuration. --></td> 179 </tr> 180</table> 181 182<p class="caution"><strong>Caution:</strong> Never save resource files directly inside the 183{@code res/} directory—it will cause a compiler error.</p> 184 185<p>For more information about certain types of resources, see the <a 186href="available-resources.html">Resource Types</a> documentation.</p> 187 188<p>The resources that you save in the subdirectories defined in table 1 are your "default" 189resources. That is, these resources define the default design and content for your application. 190However, different types of Android-powered devices might call for different types of resources. 191For example, if a device has a larger than normal screen, then you should provide 192different layout resources that take advantage of the extra screen space. Or, if a device has a 193different language setting, then you should provide different string resources that translate the 194text in your user interface. To provide these different resources for different device 195configurations, you need to provide alternative resources, in addition to your default 196resources.</p> 197 198 199<h2 id="AlternativeResources">Providing Alternative Resources</h2> 200 201 202<div class="figure" style="width:421px"> 203<img src="{@docRoot}images/resources/resource_devices_diagram2.png" height="137" alt="" /> 204<p class="img-caption"> 205<strong>Figure 1.</strong> Two different devices, one using alternative resources.</p> 206</div> 207 208<p>Almost every application should provide alternative resources to support specific device 209configurations. For instance, you should include alternative drawable resources for different 210screen densities and alternative string resources for different languages. At runtime, Android 211detects the current device configuration and loads the appropriate 212resources for your application.</p> 213 214<p>To specify configuration-specific alternatives for a set of resources:</p> 215<ol> 216 <li>Create a new directory in {@code res/} named in the form {@code 217<em><resources_name></em>-<em><config_qualifier></em>}. 218 <ul> 219 <li><em>{@code <resources_name>}</em> is the directory name of the corresponding default 220resources (defined in table 1).</li> 221 <li><em>{@code <qualifier>}</em> is a name that specifies an individual configuration 222for which these resources are to be used (defined in table 2).</li> 223 </ul> 224 <p>You can append more than one <em>{@code <qualifier>}</em>. Separate each 225one with a dash.</p> 226 </li> 227 <li>Save the respective alternative resources in this new directory. The resource files must be 228named exactly the same as the default resource files.</li> 229</ol> 230 231<p>For example, here are some default and alternative resources:</p> 232 233<pre class="classic no-pretty-print"> 234res/ 235 drawable/ <span style="color:black"> 236 icon.png 237 background.png </span> 238 drawable-hdpi/ <span style="color:black"> 239 icon.png 240 background.png </span> 241</pre> 242 243<p>The {@code hdpi} qualifier indicates that the resources in that directory are for devices with a 244high-density screen. The images in each of these drawable directories are sized for a specific 245screen density, but the filenames are exactly 246the same. This way, the resource ID that you use to reference the {@code icon.png} or {@code 247background.png} image is always the same, but Android selects the 248version of each resource that best matches the current device, by comparing the device 249configuration information with the qualifiers in the alternative resource directory name.</p> 250 251<p>Android supports several configuration qualifiers and you can 252add multiple qualifiers to one directory name, by separating each qualifier with a dash. Table 2 253lists the valid configuration qualifiers, in order of precedence—if you use multiple 254qualifiers for one resource directory, they must be added to the directory name in the order they 255are listed in the table.</p> 256 257<p class="note"><strong>Note:</strong> Some configuration qualifiers were added after Android 1.0, 258so not 259all versions of Android support all the qualifiers listed in table 2. New qualifiers 260indicate the version in which they were added. To avoid any issues, always include a set of default 261resources for resources that your application uses. For more information, see the section about <a 262href="#Compatibility">Providing the Best Device Compatibility with Resources</a>.</p> 263 264<p class="table-caption" id="table2"><strong>Table 2.</strong> Configuration qualifier 265names.</p> 266<table> 267 <tr> 268 <th>Qualifier</th> 269 <th>Values</th> 270 <th>Description</th> 271 </tr> 272 <tr id="MccQualifier"> 273 <td>MCC and MNC</td> 274 <td>Examples:<br/> 275 <code>mcc310</code><br/> 276 <code><nobr>mcc310-mnc004</nobr></code><br/> 277 <code>mcc208-mnc00</code><br/> 278 etc. 279 </td> 280 <td> 281 <p>The mobile country code (MCC), optionally followed by mobile network code (MNC) 282 from the SIM card in the device. For example, <code>mcc310</code> is U.S. on any carrier, 283 <code>mcc310-mnc004</code> is U.S. on Verizon, and <code>mcc208-mnc00</code> is France on 284 Orange.</p> 285 <p>If the device uses a radio connection (GSM phone), the MCC comes 286 from the SIM, and the MNC comes from the network to which the 287 device is connected.</p> 288 <p>You can also use the MCC alone (for example, to include country-specific legal 289resources in your application). If you need to specify based on the language only, then use the 290<em>language and region</em> qualifier instead (discussed next). If you decide to use the MCC and 291MNC qualifier, you should do so with care and test that it works as expected.</p> 292 <p>Also see the configuration fields {@link 293android.content.res.Configuration#mcc}, and {@link 294android.content.res.Configuration#mnc}, which indicate the current mobile country code 295and mobile network code, respectively.</p> 296 </td> 297 </tr> 298 <tr id="LocaleQualifier"> 299 <td>Language and region</td> 300 <td>Examples:<br/> 301 <code>en</code><br/> 302 <code>fr</code><br/> 303 <code>en-rUS</code><br/> 304 <code>fr-rFR</code><br/> 305 <code>fr-rCA</code><br/> 306 etc. 307 </td> 308 <td><p>The language is defined by a two-letter <a 309href="http://www.loc.gov/standards/iso639-2/php/code_list.php">ISO 310 639-1</a> language code, optionally followed by a two letter 311 <a 312href="http://www.iso.org/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html">ISO 313 3166-1-alpha-2</a> region code (preceded by lowercase "{@code r}"). 314 </p><p> 315 The codes are <em>not</em> case-sensitive; the {@code r} prefix is used to 316 distinguish the region portion. 317 You cannot specify a region alone.</p> 318 <p>This can change during the life 319of your application if the user changes his or her language in the system settings. See <a 320href="runtime-changes.html">Handling Runtime Changes</a> for information about 321how this can affect your application during runtime.</p> 322 <p>See <a href="localization.html">Localization</a> for a complete guide to localizing 323your application for other languages.</p> 324 <p>Also see the {@link android.content.res.Configuration#locale} configuration field, which 325indicates the current locale.</p> 326 </td> 327 </tr> 328 <tr id="ScreenSizeQualifier"> 329 <td>Screen size</td> 330 <td> 331 <code>small</code><br/> 332 <code>normal</code><br/> 333 <code>large</code> 334 </td> 335 <td> 336 <ul class="nolist"> 337 <li>{@code small}: Screens based on the space available on a 338 low-density QVGA screen. Considering a portrait HVGA display, this has 339 the same available width but less height—it is 3:4 vs. HVGA's 340 2:3 aspect ratio. Examples are QVGA low density and VGA high 341 density.</li> 342 <li>{@code normal}: Screens based on the traditional 343 medium-density HVGA screen. A screen is considered to be normal if it is 344 at least this size (independent of density) and not larger. Examples 345 of such screens a WQVGA low density, HVGA medium density, WVGA 346 high density.</li> 347 <li>{@code large}: Screens based on the space available on a 348 medium-density VGA screen. Such a screen has significantly more 349 available space in both width and height than an HVGA display. 350 Examples are VGA and WVGA medium density screens.</li> 351 </ul> 352 <p><em>Added in API Level 4.</em></p> 353 <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 354Screens</a> for more information.</p> 355 <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field, 356which indicates whether the screen is small, normal, 357or large.</p> 358 </td> 359 </tr> 360 <tr id="ScreenAspectQualifier"> 361 <td>Screen aspect</td> 362 <td> 363 <code>long</code><br/> 364 <code>notlong</code> 365 </td> 366 <td> 367 <ul class="nolist"> 368 <li>{@code long}: Long screens, such as WQVGA, WVGA, FWVGA</li> 369 <li>{@code notlong}: Not long screens, such as QVGA, HVGA, and VGA</li> 370 </ul> 371 <p><em>Added in API Level 4.</em></p> 372 <p>This is based purely on the aspect ratio of the screen (a "long" screen is wider). This 373is not related to the screen orientation.</p> 374 <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field, 375which indicates whether the screen is long.</p> 376 </td> 377 </tr> 378 <tr id="OrientationQualifier"> 379 <td>Screen orientation</td> 380 <td> 381 <code>port</code><br/> 382 <code>land</code> <!-- <br/> 383 <code>square</code> --> 384 </td> 385 <td> 386 <ul class="nolist"> 387 <li>{@code port}: Device is in portrait orientation (vertical)</li> 388 <li>{@code land}: Device is in landscape orientation (horizontal)</li> 389 <!-- Square mode is currently not used. --> 390 </ul> 391 <p>This can change during the life of your application if the user rotates the 392screen. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about 393how this affects your application during runtime.</p> 394 <p>Also see the {@link android.content.res.Configuration#orientation} configuration field, 395which indicates the current device orientation.</p> 396 </td> 397 </tr> 398 <tr id="DockQualifier"> 399 <td>Dock mode</td> 400 <td> 401 <code>car</code><br/> 402 <code>desk</code> 403 </td> 404 <td> 405 <ul class="nolist"> 406 <li>{@code car}: Device is in a car dock</li> 407 <li>{@code desk}: Device is in a desk dock</li> 408 </ul> 409 <p><em>Added in API Level 8.</em></p> 410 <p>This can change during the life of your application if the user places the device in a 411dock. You can enable or disable this mode using {@link 412android.app.UiModeManager}. See <a href="runtime-changes.html">Handling Runtime Changes</a> for 413information about how this affects your application during runtime.</p> 414 </td> 415 </tr> 416 <tr id="NightQualifier"> 417 <td>Night mode</td> 418 <td> 419 <code>night</code><br/> 420 <code>notnight</code> 421 </td> 422 <td> 423 <ul class="nolist"> 424 <li>{@code night}: Night time</li> 425 <li>{@code notnight}: Day time</li> 426 </ul> 427 <p><em>Added in API Level 8.</em></p> 428 <p>This can change during the life of your application if night mode is left in 429auto mode (default), in which case the mode changes based on the time of day. You can enable 430or disable this mode using {@link android.app.UiModeManager}. See <a 431href="runtime-changes.html">Handling Runtime Changes</a> for information about how this affects your 432application during runtime.</p> 433 </td> 434 </tr> 435 <tr id="DensityQualifier"> 436 <td>Screen pixel density (dpi)</td> 437 <td> 438 <code>ldpi</code><br/> 439 <code>mdpi</code><br/> 440 <code>hdpi</code><br/> 441 <code>nodpi</code> 442 </td> 443 <td> 444 <ul class="nolist"> 445 <li>{@code ldpi}: Low-density screens; approximately 120dpi.</li> 446 <li>{@code mdpi}: Medium-density (on traditional HVGA) screens; approximately 447160dpi.</li> 448 <li>{@code hdpi}: High-density screens; approximately 240dpi.</li> 449 <li>{@code nodpi}: This can be used for bitmap resources that you do not want to be scaled 450to match the device density.</li> 451 </ul> 452 <p><em>Added in API Level 4.</em></p> 453 <p>There is thus a 4:3 scaling factor between each density, so a 9x9 bitmap 454 in ldpi is 12x12 in mdpi and 16x16 in hdpi.</p> 455 <p>When Android selects which resource files to use, 456 it handles screen density differently than the other qualifiers. 457 In step 1 of <a href="#BestMatch">How Android finds the best 458 matching directory</a> (below), screen density is always considered to 459 be a match. In step 4, if the qualifier being considered is screen 460 density, Android selects the best final match at that point, 461 without any need to move on to step 5. 462 </p> 463 <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 464Screens</a> for more information about how to handle screen sizes and how Android might scale 465your bitmaps.</p> 466 </td> 467 </tr> 468 <tr id="TouchscreenQualifier"> 469 <td>Touchscreen type</td> 470 <td> 471 <code>notouch</code><br/> 472 <code>stylus</code><br/> 473 <code>finger</code> 474 </td> 475 <td> 476 <ul class="nolist"> 477 <li>{@code notouch}: Device does not have a touchscreen.</li> 478 <li>{@code stylus}: Device has a resistive touchscreen that's suited for use with a 479stylus.</li> 480 <li>{@code finger}: Device has a touchscreen.</li> 481 </ul> 482 <p>Also see the {@link android.content.res.Configuration#touchscreen} configuration field, 483which indicates the type of touchscreen on the device.</p> 484 </td> 485 </tr> 486 <tr id="KeyboardAvailQualifier"> 487 <td>Keyboard availability</td> 488 <td> 489 <code>keysexposed</code><br/> 490 <code>keyssoft</code> 491 </td> 492 <td> 493 <ul class="nolist"> 494 <li>{@code keysexposed}: Device has a keyboard available. If the device has a 495software keyboard enabled (which is likely), this may be used even when the hardware keyboard is 496<em>not</em> exposed to the user, even if the device has no hardware keyboard. If no software 497keyboard is provided or it's disabled, then this is only used when a hardware keyboard is 498exposed.</li> 499 <li>{@code keyshidden}: Device has a hardware keyboard available but it is 500hidden <em>and</em> the device does <em>not</em> have a software keyboard enabled.</li> 501 <li>{@code keyssoft}: Device has a software keyboard enabled, whether it's 502visible or not.</li> 503 </ul> 504 <p>If you provide <code>keysexposed</code> resources, but not <code>keyssoft</code> 505resources, the system uses the <code>keysexposed</code> resources regardless of whether a 506keyboard is visible, as long as the system has a software keyboard enabled.</p> 507 <p>This can change during the life of your application if the user opens a hardware 508keyboard. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about how 509this affects your application during runtime.</p> 510 <p>Also see the configuration fields {@link 511android.content.res.Configuration#hardKeyboardHidden} and {@link 512android.content.res.Configuration#keyboardHidden}, which indicate the visibility of a hardware 513keyboard and and the visibility of any kind of keyboard (including software), respectively.</p> 514 </td> 515 </tr> 516 <tr id="ImeQualifier"> 517 <td>Primary text input method</td> 518 <td> 519 <code>nokeys</code><br/> 520 <code>qwerty</code><br/> 521 <code>12key</code> 522 </td> 523 <td> 524 <ul class="nolist"> 525 <li>{@code nokeys}: Device has no hardware keys for text input.</li> 526 <li>{@code qwerty}: Device has a hardware qwerty keyboard, whether it's visible to the 527user 528or not.</li> 529 <li>{@code 12key}: Device has a hardware 12-key keyboard, whether it's visible to the user 530or not.</li> 531 </ul> 532 <p>Also see the {@link android.content.res.Configuration#keyboard} configuration field, 533which indicates the primary text input method available.</p> 534 </td> 535 </tr> 536 <tr id="NavAvailQualifier"> 537 <td>Navigation key availability</td> 538 <td> 539 <code>navexposed</code><br/> 540 <code>navhidden</code> 541 </td> 542 <td> 543 <ul class="nolist"> 544 <li>{@code navexposed}: Navigation keys are available to the user.</li> 545 <li>{@code navhidden}: Navigation keys are not available (such as behind a closed 546lid).</li> 547 </ul> 548 <p>This can change during the life of your application if the user reveals the navigation 549keys. See <a href="runtime-changes.html">Handling Runtime Changes</a> for 550information about how this affects your application during runtime.</p> 551 <p>Also see the {@link android.content.res.Configuration#navigationHidden} configuration 552field, which indicates whether navigation keys are hidden.</p> 553 </td> 554 </tr> 555 <tr id="TouchQualifier"> 556 <td>Primary non-touch navigation method</td> 557 <td> 558 <code>nonav</code><br/> 559 <code>dpad</code><br/> 560 <code>trackball</code><br/> 561 <code>wheel</code> 562 </td> 563 <td> 564 <ul class="nolist"> 565 <li>{@code nonav}: Device has no navigation facility other than using the 566touchscreen.</li> 567 <li>{@code dpad}: Device has a directional-pad (d-pad) for navigation.</li> 568 <li>{@code trackball}: Device has a trackball for navigation.</li> 569 <li>{@code wheel}: Device has a directional wheel(s) for navigation (uncommon).</li> 570 </ul> 571 <p>Also see the {@link android.content.res.Configuration#navigation} configuration field, 572which indicates the type of navigation method available.</p> 573 </td> 574 </tr> 575<!-- DEPRECATED 576 <tr> 577 <td>Screen dimensions</td> 578 <td>Examples:<br/> 579 <code>320x240</code><br/> 580 <code>640x480</code><br/> 581 etc. 582 </td> 583 <td> 584 <p>The larger dimension must be specified first. <strong>This configuration is deprecated 585and should not be used</strong>. Instead use "screen size," "wider/taller screens," and "screen 586orientation" described above.</p> 587 </td> 588 </tr> 589--> 590 <tr id="VersionQualifier"> 591 <td>System Version (API Level)</td> 592 <td>Examples:<br/> 593 <code>v3</code><br/> 594 <code>v4</code><br/> 595 <code>v7</code><br/> 596 etc.</td> 597 <td> 598 <p>The API Level supported by the device. For example, <code>v1</code> for API Level 5991 (devices with Android 1.0 or higher) and <code>v4</code> for API Level 4 (devices with Android 6001.6 or higher). See the <a 601href="{@docRoot}guide/appendix/api-levels.html">Android API Levels</a> document for more information 602about these values.</p> 603 <p class="caution"><strong>Caution:</strong> Android 1.5 and 1.6 only match resources 604with this qualifier when it exactly matches the system version. See the section below about <a 605href="#KnownIssues">Known Issues</a> for more information.</p> 606 </td> 607 </tr> 608</table> 609 610 611<h3 id="QualifierRules">Qualifier name rules</h3> 612 613<p>Here are some rules about using configuration qualifier names:</p> 614 615<ul> 616 <li>You can specify multiple qualifiers for a single set of resources, separated by dashes. For 617example, <code>drawable-en-rUS-land</code> applies to US-English devices in landscape 618orientation.</li> 619 <li>The qualifiers must be in the order listed in <a href="#table2">table 2</a>. For 620example: 621 <ul> 622 <li>Wrong: <code>drawable-hdpi-port/</code></li> 623 <li>Correct: <code>drawable-port-hdpi/</code></li> 624 </ul> 625 </li> 626 <li>Alternative resource directories cannot be nested. For example, you cannot have 627<code>res/drawable/drawable-en/</code>.</li> 628 <li>Values are case-insensitive. The resource compiler converts directory names 629 to lower case before processing to avoid problems on case-insensitive 630 file systems. Any capitalization in the names is only to benefit readability.</li> 631 <li>Only one value for each qualifier type is supported. For example, if you want to use 632the same drawable files for Spain and France, you <em>cannot</em> have a directory named 633<code>drawable-rES-rFR/</code>. Instead you need two resource directories, such as 634<code>drawable-rES/</code> and <code>drawable-rFR/</code>, which contain the appropriate files. 635However, you are not required to actually duplicate the same files in both locations. Instead, you 636can create an alias to a resource. See <a href="#AliasResources">Creating 637alias resources</a> below.</li> 638</ul> 639 640<p>After you save alternative resources into directories named with 641these qualifiers, Android automatically applies the resources in your application based on the 642current device configuration. Each time a resource is requested, Android checks for alternative 643resource directories that contain the requested resource file, then <a href="#BestMatch">finds the 644best-matching resource</a> (discussed below). If there are no alternative resources that match 645a particular device configuration, then Android uses the corresponding default resources (the 646set of resources for a particular resource type that does not include a configuration 647qualifier).</p> 648 649 650 651<h3 id="AliasResources">Creating alias resources</h3> 652 653<p>When you have a resource that you'd like to use for more than one device 654configuration (but do not want to provide as a default resource), you do not need to put the same 655resource in more than one alternative resource directory. Instead, you can (in some cases) create an 656alternative 657resource that acts as an alias for a resource saved in your default resource directory.</p> 658 659<p class="note"><strong>Note:</strong> Not all resources offer a mechanism by which you can 660create an alias to another resource. In particular, animation, menu, raw, and other unspecified 661resources in the {@code xml/} directory do not offer this feature.</p> 662 663<p>For example, imagine you have an application icon, {@code icon.png}, and need unique version of 664it for different locales. However, two locales, English-Canadian and French-Canadian, need to 665use the same version. You might assume that you need to copy the same image 666into the resource directory for both English-Canadian and French-Canadian, but it's 667not true. Instead, you can save the image that's used for both as {@code icon_ca.png} (any 668name other than {@code icon.png}) and put 669it in the default {@code res/drawable/} directory. Then create an {@code icon.xml} file in {@code 670res/drawable-en-rCA/} and {@code res/drawable-fr-rCA/} that refers to the {@code icon_ca.png} 671resource using the {@code <bitmap>} element. This allows you to store just one version of the 672PNG file and two small XML files that point to it. (An example XML file is shown below.)</p> 673 674 675<h4>Drawable</h4> 676 677<p>To create an alias to an existing drawable, use the {@code <bitmap>} element. 678For example:</p> 679 680<pre> 681<?xml version="1.0" encoding="utf-8"?> 682<bitmap xmlns:android="http://schemas.android.com/apk/res/android" 683 android:src="@drawable/icon_ca" /> 684</pre> 685 686<p>If you save this file as {@code icon.xml} (in an alternative resource directory, such as 687{@code res/drawable-en-rCA/}), it is compiled into a resource that you 688can reference as {@code R.drawable.icon}, but is actually an alias for the {@code 689R.drawable.icon_ca} resource (which is saved in {@code res/drawable/}).</p> 690 691 692<h4>Layout</h4> 693 694<p>To create an alias to an existing layout, use the {@code <include>} 695element, wrapped in a {@code <merge>}. For example:</p> 696 697<pre> 698<?xml version="1.0" encoding="utf-8"?> 699<merge> 700 <include layout="@layout/main_ltr"/> 701</merge> 702</pre> 703 704<p>If you save this file as {@code main.xml}, it is compiled into a resource you can reference 705as {@code R.layout.main}, but is actually an alias for the {@code R.layout.main_ltr} 706resource.</p> 707 708 709<h4>Strings and other simple values</h4> 710 711<p>To create an alias to an existing string, simply use the resource ID of the desired 712string as the value for the new string. For example:</p> 713 714<pre> 715<?xml version="1.0" encoding="utf-8"?> 716<resources> 717 <string name="hello">Hello</string> 718 <string name="hi">@string/hello</string> 719</resources> 720</pre> 721 722<p>The {@code R.string.hi} resource is now an alias for the {@code R.string.hello}.</p> 723 724<p> <a href="{@docRoot}guide/topics/resources/more-resources.html">Other simple values</a> work the 725same way. For example, a color:</p> 726 727<pre> 728<?xml version="1.0" encoding="utf-8"?> 729<resources> 730 <color name="yellow">#f00</color> 731 <color name="highlight">@color/red</color> 732</resources> 733</pre> 734 735 736 737 738<h2 id="Compatibility">Providing the Best Device Compatibility with Resources</h2> 739 740<p>In order for your application to support multiple device configurations, it's very important that 741you always provide default resources for each type of resource that your application uses.</p> 742 743<p>For example, if your application supports several languages, always include a {@code 744values/} directory (in which your strings are saved) <em>without</em> a <a 745href="#LocalQualifier">language and region qualifier</a>. If you instead put all your string files 746in directories that have a language and region qualifier, then your application will crash when run 747on a device set to a language that your strings do not support. But, as long as you provide default 748{@code values/} resources, then your application will run properly (even if the user doesn't 749understand that language—it's better than crashing).</p> 750 751<p>Likewise, if you provide different layout resources based on the screen orientation, you should 752pick one orientation as your default. For example, instead of providing layout resources in {@code 753layout-land/} for landscape and {@code layout-port/} for portrait, leave one as the default, such as 754{@code layout/} for landscape and {@code layout-port/} for portrait.</p> 755 756<p>Providing default resources is important not only because your application might run on a 757configuration you had not anticipated, but also because new versions of Android sometimes add 758configuration qualifiers that older versions do not support. If you use a new resource qualifier, 759but maintain code compatibility with older versions of Android, then when an older version of 760Android runs your application, it will crash if you do not provide default resources, because it 761cannot use the resources named with the new qualifier. For example, if your <a 762href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code 763minSdkVersion}</a> is set to 4, and you qualify all of your drawable resources using <a 764href="NightQualifier">night mode</a> ({@code night} or {@code notnight}, which were added in API 765Level 8), then an API Level 4 device cannot access your drawable resources and will crash. In this 766case, you probably want {@code notnight} to be your default resources, so you should exclude that 767qualifier so your drawable resources are in either {@code drawable/} or {@code drawable-night/}.</p> 768 769<p>So, in order to provide the best device compatibility, always provide default 770resources for the resources your application needs to perform properly. Then create alternative 771resources for specific device configurations using the configuration qualifiers.</p> 772 773<p>There is one exception to this rule: If your application's <a 774href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is 4 or 775greater, you <em>do not</em> need default drawable resources when you provide alternative drawable 776resources with the <a href="#DensityQualifier">screen density</a> qualifier. Even without default 777drawable resources, Android can find the best match among the alternative screen densities and scale 778the bitmaps as necessary. However, for the best experience on all types of devices, you should 779provide alternative drawables for all three types of density. If your <a 780href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is 781<em>less than</em> 4 (Android 1.5 or lower), be aware that the screen size, density, and aspect 782qualifiers are not supported on Android 1.5 or lower, so you might need to perform additional 783compatibility for these versions.</p> 784 785 786<h3 id="ScreenCompatibility">Providing screen resource compatibility for Android 1.5</h3> 787 788<p>Android 1.5 (and lower) does not support the following resource qualifers:</p> 789<dl> 790 <dt><a href="#DensityQualifier">Density</a></dt> 791 <dd>{@code ldpi}, {@code mdpi}, {@code ldpi}, and {@code nodpi}</dd> 792 <dt><a href="#ScreenSizeQualifier">Screen size</a></dt> 793 <dd>{@code small}, {@code normal}, and {@code large}</dd> 794 <dt><a href="#ScreenAspectQualifier">Screen aspect</a></dt> 795 <dd>{@code long} and {@code notlong}</dd> 796</dl> 797 798<p>These resource qualifiers were introduced in Android 1.6, so Android 1.5 (API Level 3) and lower 799does not support them. If you use these configuration qualifiers and do not provide 800corresponding default resources, then an Android 1.5 device might use any one of the resource 801directories named with the above screen qualifiers, because it ignores the screen qualifiers and 802uses whichever otherwise-matching drawable resource it finds first.</p> 803 804<p>For example, if your application supports Android 1.5 and includes drawable resources for 805each density type ({@code drawable-ldpi/}, {@code drawable-mdpi/}, and {@code drawable-ldpi/}), 806and does <em>not</em> include default drawable resources ({@code drawable/}), then 807an Android 1.5 will use drawables from any one of the alternative resource directories, which 808can result in a user interface that's less than ideal.<p> 809 810<p>So, to provide compatibility with Android 1.5 (and lower) when using the screen configuration 811qualifiers:</p> 812<ol> 813 <li>Provide default resources that are for medium-density, normal, and notlong screens. 814 815 <p>Because all Android 1.5 devices have medium-density, normal, not-long screens, you can 816place these kinds of resources in the corresponding default resource directory. For example, put all 817medium density drawable resources in {@code drawable/} (instead of {@code drawable-mdpi/}), 818put {@code normal} size resources in the corresponding default resource directory, and {@code 819notlong} resources in the corresponding default resource directory.</p> 820 </li> 821 822 <li>Ensure that your <a href="{@docRoot}sdk/tools-notes.html">SDK Tools</a> version 823is r6 or greater. 824 825 <p>You need SDK Tools, Revision 6 (or greater), because it includes a new packaging tool that 826automatically applies an appropriate <a href="#VersionQualifier">version qualifier</a> to any 827resource directory named with a qualifier that does not exist in Android 1.0. For example, because 828the density qualifier was introduced in Android 1.6 (API Level 4), when the packaging tool 829encounters a resource directory using the density qualifier, it adds {@code v4} to the directory 830name to ensure that older versions do not use those resources (only API Level 4 and higher support 831that qualifier). Thus, by putting your medium-density resources in a directory <em>without</em> the 832{@code mdpi} qualifier, they are still accessible by Android 1.5, and any device that supports the 833density qualifer and has a medium-density screen also uses the default resources (which are mdpi) 834because they are the best match for the device (instead of using the {@code ldpi} or {@code hdpi} 835resources).</p> 836</li> 837</ol> 838 839<p class="note"><strong>Note:</strong> Later versions of Android, such as API Level 8, 840introduce other configuration qualifiers that older version do not support. To provide the best 841compatibility, you should always include a set of default resources for each type of resource 842that your application uses, as discussed above to provide the best device compatibility.</p> 843 844 845 846<h2 id="BestMatch">How Android Finds the Best-matching Resource</h2> 847 848<p>When you request a resource for which you provide alternatives, Android selects which 849alternative resource to use at runtime, depending on the current device configuration. To 850demonstrate how Android selects an alternative resource, assume the following drawable directories 851each contain different versions of the same images:</p> 852 853<pre class="classic no-pretty-print"> 854drawable/ 855drawable-en/ 856drawable-fr-rCA/ 857drawable-en-port/ 858drawable-en-notouch-12key/ 859drawable-port-ldpi/ 860drawable-port-notouch-12key/ 861</pre> 862 863<p>And assume the following is the device configuration:</p> 864 865<p style="margin-left:1em;"> 866Locale = <code>en-GB</code> <br/> 867Screen orientation = <code>port</code> <br/> 868Screen pixel density = <code>hdpi</code> <br/> 869Touchscreen type = <code>notouch</code> <br/> 870Primary text input method = <code>12key</code> 871</p> 872 873<p>By comparing the device configuration to the available alternative resources, Android selects 874drawables from {@code drawable-en-port}. It arrives at this decision using the following logic:</p> 875 876 877<div class="figure" style="width:280px"> 878<img src="{@docRoot}images/resources/res-selection-flowchart.png" alt="" height="590" /> 879<p class="img-caption"><strong>Figure 2.</strong> Flowchart of how Android finds the 880best-matching resource.</p> 881</div> 882 883 884<ol> 885 <li>Eliminate resource files that contradict the device configuration. 886 <p>The <code>drawable-fr-rCA/</code> directory is eliminated, because it 887contradicts the <code>en-GB</code> locale.</p> 888<pre class="classic no-pretty-print"> 889drawable/ 890drawable-en/ 891<strike>drawable-fr-rCA/</strike> 892drawable-en-port/ 893drawable-en-notouch-12key/ 894drawable-port-ldpi/ 895drawable-port-notouch-12key/ 896</pre> 897<p class="note"><strong>Exception:</strong> Screen pixel density is the one qualifier that is not 898eliminated due to a contradiction. Even though the screen density of the device is mdpi, 899<code>drawable-port-ldpi/</code> is not eliminated because every screen density is 900considered to be a match at this point. More information is available in the <a 901href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 902Screens</a> document.</p></li> 903 904 <li>Pick the (next) highest-precedence qualifier in the list (<a href="#table2">table 2</a>). 905(Start with MCC, then move down.) </li> 906 <li>Do any of the resource directories include this qualifier? </li> 907 <ul> 908 <li>If No, return to step 2 and look at the next qualifier. (In the example, 909 the answer is "no" until the language qualifier is reached.)</li> 910 <li>If Yes, continue to step 4.</li> 911 </ul> 912 </li> 913 914 <li>Eliminate resource directories that do not include this qualifier. In the example, the system 915eliminates all the directories that do not include a language qualifier:</li> 916<pre class="classic no-pretty-print"> 917<strike>drawable/</strike> 918drawable-en/ 919drawable-en-port/ 920drawable-en-notouch-12key/ 921<strike>drawable-port-ldpi/</strike> 922<strike>drawable-port-notouch-12key/</strike> 923</pre> 924<p class="note"><strong>Exception:</strong> If the qualifier in question is screen pixel density, 925Android 926selects the option that most closely matches the device, and the selection process is complete. 927In general, Android prefers scaling down a larger original image to scaling up a smaller 928original image. See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple 929Screens</a>.</p> 930 </li> 931 932 <li>Go back and repeat steps 2, 3, and 4 until only one directory remains. In the example, screen 933orientation is the next qualifier for which there are any matches. 934So, resources that do not specify a screen orientation are eliminated: 935<pre class="classic no-pretty-print"> 936<strike>drawable-en/</strike> 937drawable-en-port/ 938<strike>drawable-en-notouch-12key/</strike> 939</pre> 940<p>The remaining directory is {@code drawable-en-port}.</p> 941 </li> 942</ol> 943 944<p>Though this procedure is executed for each resource requested, the system further optimizes 945some aspects. One such optimization is that once the device configuration is known, it might 946eliminate alternative resources that can never match. For example, if the configuration 947language is English ("en"), then any resource directory that has a language qualifier set to 948something other than English is never included in the pool of resources checked (though a 949resource directory <em>without</em> the language qualifier is still included).</p> 950 951<p class="note"><strong>Note:</strong> The <em>precedence</em> of the qualifier (in <a 952href="#table2">table 2</a>) is more important 953than the number of qualifiers that exactly match the device. For example, in step 4 above, the last 954choice on the list includes three qualifiers that exactly match the device (orientation, touchscreen 955type, and input method), while <code>drawable-en</code> has only one parameter that matches 956(language). However, language has a higher precedence than these other qualifiers, so 957<code>drawable-port-notouch-12key</code> is out.</p> 958 959<p>To learn more about how to use resources in your application, continue to <a 960href="accessing-resources.html">Accessing Resources</a>.</p> 961 962 963 964 965<h2 id="KnownIssues">Known Issues</h2> 966 967<h3>Android 1.5 and 1.6: Version qualifier performs exact match, instead of best match</h3> 968 969<p>The correct behavior is for the system to match resources marked with a <a 970href="#VersionQualifier">version qualifier</a> equal 971to or less than the system version on the device, but on Android 1.5 and 1.6, (API Level 3 and 4), 972there is a bug that causes the system to match resources marked with the version qualifier 973only when it exactly matches the version on the device.</p> 974 975<p><b>The workaround:</b> To provide version-specific resources, abide by this behavior. However, 976because this bug is fixed in versions of Android available after 1.6, if 977you need to differentiate resources between Android 1.5, 1.6, and later versions, then you only need 978to apply the version qualifier to the 1.6 resources and one to match all later versions. Thus, this 979is effectively a non-issue.</p> 980 981<p>For example, if you want drawable resources that are different on each Android 1.5, 1.6, 982and 2.0.1 (and later), create three drawable directories: {@code drawable/} (for 1.5 and lower), 983{@code drawable-v4} (for 1.6), and {@code drawable-v6} (for 2.0.1 and later—version 2.0, v5, 984is no longer available).</p> 985 986 987