App resources overview (Views)

Concepts and Jetpack Compose implementation

Resources are the additional files and static content that your code uses, such as bitmaps, layout definitions, user interface strings, animation instructions, and more.

Always externalize app resources such as images and strings from your code, so that you can maintain them independently. Also, provide alternative resources for specific device configurations by grouping them in specially named resource directories. At runtime, Android uses the appropriate resource based on the current configuration. For example, you might want to provide a different UI layout depending on the screen size or different strings depending on the language setting.

Once you externalize your app resources, you can access them using resource IDs that are generated in your project's R class. This document shows you how to group the resources in your Android project. It also shows you how to provide alternative resources for specific device configurations and then access them from your app code or other XML files.

Group resource types

Place each type of resource in a specific subdirectory of your project's res/ directory. For example, here's the file hierarchy for a simple project:

MyProject/
    src/
        MyActivity.java
    res/
        drawable/
            graphic.png
        layout/
            main.xml
            info.xml
        mipmap/
            icon.png
        values/
            strings.xml

The res/ directory contains all the resources in its subdirectories: an image resource, two layout resources, a mipmap/ directory for launcher icons, and a string resource file. The resource directory names are important and are described in table 1.

Table 1. Resource directories supported inside project res/ directory.

Directory

Resource Type

animator/

XML files that define Property animations.

anim/

XML files that define Tween animations. Property animations can also be saved in this directory, but the animator/ directory is preferred for property animations to distinguish between the two types.

color/

XML files that define a state list of colors. For more information, see Color state list resource.

drawable/

Bitmap files (PNG, .9.png, JPG, or GIF) or XML files that are compiled into the following drawable resource subtypes:

  • Bitmap files
  • Nine-patches (re-sizable bitmaps)
  • State lists
  • Shapes
  • Animation drawables
  • Other drawables

For more information, see Drawable resources.

mipmap/

Drawable files for different launcher icon densities. For more information on managing launcher icons with mipmap/ folders, see Put app icons in mipmap directories.

layout/

XML files that define a user interface layout. For more information, see Layout resource.

menu/

XML files that define app menus, such as an options menu, context menu, or submenu. For more information, see Menu resource.

raw/

Arbitrary files to save in their raw form. To open these resources with a raw InputStream, call Resources.openRawResource with the resource ID, which is R.raw.filename.

However, if you need access to the original filenames and file hierarchy, consider saving resources in the assets/ directory instead of res/raw/. Files in assets/ aren't given a resource ID, so you can only read them using AssetManager.

values/

XML files that contain simple values, such as strings, integers, and colors.

Whereas XML resource files in other res/ subdirectories define a single resource based on the XML filename, files in the values/ directory describe multiple resources. For a file in this directory, each child of the element defines a single resource. For example, a element creates an R.string resource, and a element creates an R.color resource.

Because each resource is defined with its own XML element, you can name the file whatever you want and place different resource types in one file. However, for clarity, you might want to place unique resource types in different files. For example, here are some filename conventions for resources you can create in this directory:

For more information, see String resources, Style resource, and More resource types.

xml/

Arbitrary XML files that can be read at runtime by calling Resources.getXML(). Various XML configuration files must be saved here.

font/

Font files with extensions such as TTF, OTF, or TTC or XML files that include a element. For more information about fonts as resources, see Add a font as an XML resource.

The resources that you save in the subdirectories defined in table 1 are your default resources. That is, these resources define the default design and content for your app. However, different types of Android-powered devices might call for different types of resources.

For example, you can provide different layout resources for devices that have larger than normal screens to take advantage of the extra screen space. You can also provide different string resources that translate the text in your user interface based on the device's language setting. To provide these different resources for different device configurations, you need to provide alternative resources in addition to your default resources.

Provide alternative resources

Most apps provide alternative resources to support specific device configurations. For instance, include alternative drawable resources for different screen densities and alternative string resources for different languages. At runtime, Android detects the current device configuration and loads the appropriate resources for your app.

Figure 1. Two devices using different layout resources based on screen size.

To specify configuration-specific alternatives for a set of resources, do the following:

  1. Create a new directory in res/ named in the form <resources_name>-<qualifier>.

    • <resources_name> is the directory name of the corresponding default resources (defined in table 1).
    • <qualifier> is a name that specifies an individual configuration for which these resources are to be used (defined in table 2).

    You can append more than one <qualifier>. Separate each one with a dash.

  2. Save the appropriate alternative resources in this new directory. The resource files must be named exactly the same as the default resource files.

For example, here are some default and alternative resources:

res/
    drawable/
        icon.png
        background.png
    drawable-hdpi/
        icon.png
        background.png

The hdpi qualifier indicates that the resources in that directory are for devices with a high-density screen. The images in these drawable directories are sized for specific screen densities, but the filenames are exactly the same. This way, the resource ID that you use to reference the icon.png or background.png image is always the same. Android selects the version of each resource that best matches the current device by comparing the device configuration information with the qualifiers in the resource directory name.

Table 2 lists the valid configuration qualifiers in order of precedence. You can add multiple qualifiers to one directory name by separating each qualifier with a dash. If you use multiple qualifiers for a resource directory, you must add them to the directory name in the order they are listed in the table.

Table 2. Configuration qualifier names.

Configuration

Qualifier values

Description

MCC and MNC

Examples:

mcc310

mcc310-mnc004

mcc208-mnc00

The mobile country code (MCC), optionally followed by the mobile network code (MNC) from the SIM card in the device. For example, mcc310 is U.S. on any carrier, mcc310-mnc004 is U.S. on Verizon, and mcc208-mnc00 is France on Orange.

If the device uses a radio connection (that is, it's a GSM phone), the MCC and MNC values come from the SIM card.

You can also use the MCC alone, for example, to include country-specific legal resources in your app. If you need to specify based on the language only, then use the language, script (optional), and region (optional) qualifier instead. If you use the MCC and MNC qualifier, do so with care and test that it works as expected.

Also see the configuration fields mcc and mnc, which indicate the current mobile country code and mobile network code, respectively.

Language, script (optional), and region (optional)

Examples:

en

fr

en-rUS

fr-rFR

fr-rCA

b+en

b+en+US

b+es+419

b+zh+Hant

b+sr+Latn+RS

The language is defined by a two-letter ISO 639-2{:.external} language code, optionally followed by a two-letter ISO 3166-1-alpha-2{:.external} region code (preceded by lowercase r).

The codes are not case-sensitive. The r prefix is used to distinguish the region portion. You can't specify a region alone.

Android 7.0 (API level 24) introduced support for BCP 47 language tags{:.external}, which you can use to qualify language- and region-specific resources. A language tag is composed from a sequence of one or more subtags, each of which refines or narrows the range of language identified by the overall tag. For more information about language tags, see Tags for Identifying Languages{:.external}.

To use a BCP 47 language tag, concatenate b+ and a two-letter ISO 639-2{:.external} language code, optionally followed by additional subtags separated by +.

The language tag can change during the life of your app if users change their language in the system settings. For information about how this can affect your app during runtime, see Handle configuration changes.

For a complete guide to localizing your app for other languages, see Localize your app.

Also see the getLocales method, which provides the defined list of locales. This list includes the primary locale.
Grammatical gender masculine
feminine
neuter

The user's grammatical gender. Used for languages that have grammatical gender.

For example, if you need to provide different resources for French speaking users, then you can use directories like the following:

res/
  values-fr/
    strings.xml (default strings with unspecified gender)
  values-fr-masculine/
    strings.xml (strings with masculine gender)
  values-fr-feminine/
    strings.xml (strings with feminine gender)
  values-fr-neuter/
    strings.xml (strings with neutral gender)

See: Grammatical Inflection in Android.

Also see the getGrammaticalGender() configuration method, which indicates the grammatical gender.

Added in API level 34.

Layout direction

ldrtl

ldltr

The layout direction of your app. ldrtl means "layout-direction-right-to-left." ldltr means "layout-direction-left-to-right" and is the default implicit value.

This can apply to any resource, such as layouts, drawables, or values.

For example, if you want to provide a specific layout for the Arabic language and a generic layout for any other "right-to-left" language, like Persian or Hebrew, then you use directories like the following:

res/
layout/
main.xml (default layout)
layout-ar/
main.xml (specific layout for Arabic)
layout-ldrtl/
main.xml (any right-to-left language except for Arabic, because the "ar" language qualifier has a higher precedence)

Note: To enable right-to-left layout features for your app, you must set SupportsRtl to "true" and set TargetSdkVersion to 17 or higher.

Added in API level 17.

Smallest width

swdp

Examples:

sw320dp

sw600dp

sw720dp

etc.

The shortest dimension of the screen area available to an app. Specifically, the app window's smallestWidth is the shortest of the window's available height and width. You can also think of it as the "smallest possible width" for the window. You can use this qualifier so that your app has at least dps of width available for its UI.

For example, if your layout requires that its smallest dimension of screen area be at least 600 dp at all times, then you can use this qualifier to create the layout resources in a res/layout-sw600dp/ directory. The system uses these resources only when the smallest dimension of available screen is at least 600 dp, regardless of whether the 600 dp side is the user-perceived height or width. The smallest width can change if the window is resized, changing the available width/height, or repositioned, potentially changing the system insets.

Using smallest width to determine the general screen size is useful because width is often the driving factor in designing a layout. A UI often scrolls vertically, but has fairly hard constraints on the minimum space it needs horizontally.

The available width is also the key factor in determining whether to use a one-pane layout for handsets or a multipane layout for tablets. Thus, you likely care most about what the smallest possible width is on each device.

The smallest width of a device takes into account screen decorations and system UI. For example, if the device has persistent UI elements on the screen that account for space along the axis of the smallest width, the system declares the smallest width to be smaller than the actual screen size, because those are screen pixels not available for your UI.

Some values you might use here for common screen sizes:

  • 320, for devices with screen configurations such as:
    • 240x320 ldpi (QVGA handset)
    • 320x480 mdpi (handset)
    • 480x800 hdpi (high-density handset)
  • 480, for screens such as 480x800 mdpi (tablet/handset)
  • 600, for screens such as 600x1024 mdpi (7" tablet)
  • 720, for screens such as 720x1280 mdpi (10" tablet)

When your app provides multiple resource directories with different values for the smallestWidth qualifier, the system uses the one closest to (without exceeding) the device's smallestWidth.

Added in API level 13.

Also see the android:requiresSmallestWidthDp attribute, which declares the minimum smallestWidth with which your app is compatible, and the smallestScreenWidthDp configuration field, which holds the device's smallestWidth value.

For more information about designing for different screens using this qualifier, see Responsive/adaptive design with views.

Available width and height

wdp

hdp

Examples:

w720dp

w1024dp

h720dp

h1024dp

etc.

Specifies the minimum available screen width or height (in dp units defined by the value) at which the resource is used. These configuration values are compared to the current display width and height as the device orientation changes between portrait and landscape, the device folds or unfolds, or the system enters or exits multi-window mode. In multi-window mode, the values reflect the width and height of the window that contains the app, not the width and height of the device screen. Similarly, for embedded activities, the values pertain to the width and height of the individual activities, not the width and height of the screen. For more information, see Activity embedding.

Available width and height are often useful for determining whether to use a multipane layout, because even on a tablet device you often don't want the same multipane layout for portrait orientation as you do for landscape. Thus, you can use these to specify the minimum width and/or height required for the layout, instead of using both the screen size and orientation qualifiers together.

When your app provides multiple resource directories with different values for these configurations, the system uses the one closest to (without exceeding) the device's current screen width. Closest to is determined by adding the differences between the actual screen width and the specified width to the difference between the actual screen height and the specified height, with unspecified heights and widths having a value of 0.

The values exclude the area occupied by Window insets, so if the device has persistent UI elements on the edges of the display, the values for width and height are smaller than the real screen dimensions, even when the app is displayed edge to edge using Window.setDecorFitsSystemWindows or WindowCompat.setDecorFitsSystemWindows.

Some vertical screen decorations that aren't fixed (such as a phone status bar that can be hidden when full screen) are not accounted for here, nor are window decorations like the title bar or action bar, so apps must be prepared to deal with a somewhat smaller space than they specify.

Note: The system chooses the resource that matches both in width and height. Therefore a resource that specifies both is strongly preferred over one that specifies only one or the other. For example, if the actual screen is 720 dp wide by 1280 dp high and one resource is qualified with w720dp and another is qualified as w700dp-h1200dp, the latter is chosen even though the former is an exact match for what it specifies.

Added in API level 13.

Also see the screenWidthDp and screenHeightDp configuration fields, which hold the current screen width and height.

For more information about designing for different screens using this qualifier, see Responsive/adaptive design with views.

Screen size

small

normal

large

xlarge
  • small: screens that are of similar size to a low-density QVGA screen. The minimum layout size for a small screen is approximately 320x426 dp units. Examples are QVGA low density and VGA high density.
  • normal: screens that are of similar size to a medium-density HVGA screen. The minimum layout size for a normal screen is approximately 320x470 dp units. Examples of such screens are a WQVGA low density, HVGA medium density, and WVGA high density.
  • large: screens that are of similar size to a medium-density VGA screen. The minimum layout size for a large screen is approximately 480x640 dp units. Examples are VGA and WVGA medium-density screens.
  • xlarge: screens that are considerably larger than the traditional medium-density HVGA screen. The minimum layout size for an xlarge screen is approximately 720x960 dp units. In most cases, devices with extra-large screens are too large to carry in a pocket and most likely are tablet-style devices. Added in API level 9.

Note: Using a size qualifier does not imply that the resources are only for screens of that size. If you don't provide alternative resources with qualifiers that better match the current device configuration, the system can use whichever resources are the best match.

Caution: If all your resources use a size qualifier that is larger than the current screen, the system doesn't use them and your app crashes at runtime. This happens, for example, if all layout resources are tagged with the xlarge qualifier but the device has a normal-size screen.

Added in API level 4.

Also see the screenLayout configuration field, which indicates whether the screen is small, normal, or large.

For more information, see Screen compatibility overview.

Screen aspect

long

notlong
  • long: long screens, such as WQVGA, WVGA, FWVGA
  • notlong: not long screens, such as QVGA, HVGA, and VGA

Added in API level 4.

This is based purely on the aspect ratio of the screen (a long screen is wider). This isn't related to the screen orientation.

Also see the screenLayout configuration field, which indicates whether the screen is long.

Round screen

round

notround
  • round: round screens, such as a round wearable device
  • notround: rectangular screens, such as phones or tablets

Added in API level 23.

Also see the isScreenRound configuration method, which indicates whether the screen is round.

Wide Color Gamut

widecg

nowidecg
  • widecg: displays with a wide color gamut such as Display P3 or AdobeRGB
  • nowidecg: displays with a narrow color gamut such as sRGB

Added in API level 26.

Also see the isScreenWideColorGamut configuration method, which indicates whether the screen has a wide color gamut.

High Dynamic Range (HDR)

highdr

lowdr
  • highdr: displays with a high dynamic range
  • lowdr: displays with a low/standard dynamic range

Added in API level 26.

Also see the isScreenHdr configuration method, which indicates whether the screen has HDR capabilities.

Screen orientation

port

land
  • port: device is in portrait orientation (vertical)
  • land: device is in landscape orientation (horizontal)

This can change during the life of your app if the user rotates the screen. For information about how this affects your app during runtime, see Handle configuration changes.

Also see the orientation configuration field, which indicates the current device orientation.

UI mode

car

desk

television

appliance

watch

vrheadset
  • car: device is displaying in a car dock
  • desk: device is displaying in a desk dock
  • television: device is displaying on a television, providing a "ten-foot" experience where its UI is on a large screen that the user is far away from, and the experience is primarily oriented around D-pad or other non-pointer interaction
  • appliance: device is serving as an appliance, with no display
  • watch: device has a display and is worn on the wrist
  • vrheadset: device is displaying in a virtual reality headset

Added in API level 8; television added in API 13; appliance added in API 16; watch added in API 20; vrheadset added in API 26.

For information about how your app can respond when the device is inserted into or removed from a dock, read Determine and monitor the docking state and type.

This can change during the life of your app if the user places the device in a dock. You can enable or disable some of these modes using UiModeManager. For information about how this affects your app during runtime, see Handle configuration changes.

Night mode

night

notnight
  • night: night time
  • notnight: day time

Added in API level 8.

This can change during the life of your app if night mode is left in auto mode (default), in which case the mode changes based on the time of day. You can enable or disable this mode using UiModeManager. For information about how this affects your app during runtime, see Handle configuration changes.

Screen pixel density (dpi)

ldpi

mdpi

hdpi

xhdpi

xxhdpi

xxxhdpi

nodpi

tvdpi

anydpi

nnndpi
  • ldpi: low-density screens; approximately 120 dpi.
  • mdpi: medium-density (on traditional HVGA) screens; approximately 160 dpi.
  • hdpi: high-density screens; approximately 240 dpi.
  • xhdpi: extra-high-density screens; approximately 320 dpi. Added in API level 8.
  • xxhdpi: extra-extra-high-density screens; approximately 480 dpi. Added in API level 16.
  • xxxhdpi: extra-extra-extra-high-density uses (launcher icon only—see Support different pixel densities); approximately 640 dpi. Added in API level 18.
  • nodpi: used for bitmap resources that you don't want to be scaled to match the device density.
  • tvdpi: screens somewhere between mdpi and hdpi; approximately 213 dpi. This isn't considered a "primary" density group. It is mostly intended for 720p televisions, and most apps don't need it. For 1080p TV panels, use xhdpi, and for 4K TV panels, use xxxhdpi. Added in API level 13.
  • anydpi: matches all screen densities and takes precedence over other qualifiers. This is useful for vector drawables. Added in API level 21.
  • nnndpi: used to represent non-standard densities, where nnn is a positive integer screen density. This isn't used in most cases. Using standard density buckets greatly reduces the overhead of supporting the various device screen densities on the market.

There is a 3:4:6:8:12:16 scaling ratio between the six primary densities (ignoring the tvdpi density). So, a 9x9 bitmap in ldpi is 12x12 in mdpi, 18x18 in hdpi, 24x24 in xhdpi, and so on.

Note: Using a density qualifier doesn't imply that the resources are only for screens of that density. If you don't provide alternative resources with qualifiers that better match the current device configuration, the system uses whichever resources are the best match.

For more information about how to handle different screen densities and how Android might scale your bitmaps to fit the current density, see Screen compatibility overview.

Touchscreen type

notouch

finger
  • notouch: device doesn't have a touchscreen.
  • finger: device has a touchscreen that is intended to be used through direct interaction of the user's finger.

Also see the touchscreen configuration field, which indicates the type of touchscreen on the device.

Keyboard availability

keysexposed

keyshidden

keyssoft
  • keysexposed: device has a keyboard available. If the device has a software keyboard enabled (which is likely), this is used even when the hardware keyboard isn't exposed to the user or when the device has no hardware keyboard. If no software keyboard is provided or it's disabled, then this is only used when a hardware keyboard is exposed.
  • keyshidden: device has a hardware keyboard available but it is hidden and the device does not have a software keyboard enabled.
  • keyssoft: device has a software keyboard enabled, whether it's visible or not.

If you provide keysexposed resources, but not keyssoft resources, the system uses the keysexposed resources regardless of whether a keyboard is visible, as long as the system has a software keyboard enabled.

This can change during the life of your app if the user opens a hardware keyboard. For information about how this affects your app during runtime, see Handle configuration changes.

Also see the configuration fields hardKeyboardHidden and keyboardHidden, which indicate the visibility of a hardware keyboard and the visibility of any kind of keyboard (including software), respectively.

Primary text input method

nokeys

qwerty

12key
  • nokeys: device has no hardware keys for text input.
  • qwerty: device has a hardware QWERTY keyboard, whether it's visible to the user or not.
  • 12key: device has a hardware 12-key keyboard, whether it's visible to the user or not.

Also see the keyboard configuration field, which indicates the primary text input method available.

Navigation key availability

navexposed

navhidden
  • navexposed: navigation keys are available to the user.
  • navhidden: navigation keys aren't available (such as behind a closed lid).

This can change during the life of your app if the user reveals the navigation keys. For information about how this affects your app during runtime, see Handle configuration changes.

Also see the navigationHidden configuration field, which indicates whether the navigation keys are hidden.

Primary non-touch navigation method

nonav

dpad

trackball

wheel
  • nonav: device has no navigation facility other than using the touchscreen.
  • dpad: device has a directional-pad (D-pad) for navigation.
  • trackball: device has a trackball for navigation.
  • wheel: device has a directional wheel(s) for navigation (uncommon).

Also see the navigation configuration field, which indicates the type of navigation method available.

Platform version (API level)

Examples:

v3

v4

v7

etc.

The API level supported by the device. For example, v1 for API level 1 (devices with Android 1.0 or higher) and v4 for API level 4 (devices with Android 1.6 or higher). For more information about these values, see the Android API levels document.

Qualifier name rules

Here are some rules about using configuration qualifier names:

  • You can specify multiple qualifiers for a single set of resources, separated by dashes. For example, drawable-en-rUS-land applies to US-English devices in landscape orientation.
  • The qualifiers must be in the order listed in table 2.
    • Wrong: drawable-hdpi-port/
    • Correct: drawable-port-hdpi/
  • Alternative resource directories can't be nested. For example, you can't have res/drawable/drawable-en/.
  • Values are case-insensitive. The resource compiler converts directory names to lowercase before processing to avoid problems on case-insensitive file systems. Any capitalization in the names is only to benefit readability.
  • Only one value for each qualifier type is supported. For example, if you want to use the same drawable files for Spain and France, you can't have a directory named drawable-es-fr/. Instead, you need two resource directories, such as drawable-es/ and drawable-fr/, which contain the appropriate files. However, you aren't required to actually duplicate the files in both locations. Instead, you can create an alias to a resource, as described in the Create alias resources section.

After you save alternative resources into directories named with these qualifiers, Android automatically applies the resources in your app based on the current device configuration. Each time a resource is requested, Android checks for alternative resource directories that contain the requested resource file, then finds the best-matching resource.

If there are no alternative resources that match a particular device configuration, then Android uses the corresponding default resources—the set of resources for a particular resource type that doesn't include a configuration qualifier.

Create alias resources

When you have a resource that you'd like to use for more than one device configuration but you don't want to provide it as a default resource, you don't need to put the same resource in more than one alternative resource directory. Instead, you can create an alternative resource that acts as an alias for a resource saved in your default resource directory.

For example, imagine you have an app icon, icon.png, and need a unique version of it for different locales. However, two locales, English-Canadian and French-Canadian, need to use the same version. You don't need to copy the same image into the resource directory for both English-Canadian and French-Canadian. Instead, you can save the image that's used for both using any name other than icon.png, such as icon_ca.png, and put it in the default res/drawable/ directory. Then create an icon.xml file in res/drawable-en-rCA/ and res/drawable-fr-rCA/ that refers to the icon_ca.png resource using the <bitmap> element. This lets you store just one version of the PNG file and two small XML files that point to it. See the examples in the following sections for details.

Drawable

To create an alias to an existing drawable, use the <drawable> element:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <drawable name="icon">@drawable/icon_ca</drawable>
</resources>

If you save this file as icon.xml in an alternative resource directory, such as res/values-en-rCA/, it is compiled into a resource that you can reference as R.drawable.icon, but is actually an alias for the R.drawable.icon_ca resource, which is saved in res/drawable/.

Layout

To create an alias to an existing layout, use the <include> element, wrapped in a <merge>:

<?xml version="1.0" encoding="utf-8"?>
<merge>
  <include layout="@layout/main_ltr"/>
</merge>

If you save this file as main.xml, it is compiled into a resource you can reference as R.layout.main, but is actually an alias for the R.layout.main_ltr resource.

Access your app resources

Once you provide a resource in your application, you can apply it by referencing its resource ID. All resource IDs are defined in your project's R class, which the aapt tool automatically generates.

When your application is compiled, aapt generates the R class, which contains resource IDs for all the resources in your res/ directory. For each type of resource, there is an R subclass, such as R.drawable for all drawable resources. And for each resource of that type, there is a static integer, for example, R.drawable.icon. This integer is the resource ID that you can use to retrieve your resource.

Although the R class is where resource IDs are specified, you don't need to look there to discover a resource ID. A resource ID is always composed of the following:

  • The resource type: each resource is grouped into a "type," such as string, drawable, and layout. For more information about the different types, see Resource types overview.
  • The resource name, which is either the filename excluding the extension or the value in the XML android:name attribute, if the resource is a simple value, such as a string.

There are two ways you can access a resource:

  • In code: using a static integer from a subclass of your R class, such as: R.string.hello string is the resource type and hello is the resource name. There are many Android APIs that can access your resources when you provide a resource ID in this format. For more information, see the Access resources in code section.
  • In XML: using a special XML syntax that corresponds to the resource ID defined in your R class, such as: @string/hello string is the resource type and hello is the resource name. You can use this syntax in an XML resource any place where a value is expected that you provide in a resource. For more information, see the Access resources from XML section.

Access resources in code

You can use a resource in code by passing the resource ID as a method parameter. For example, you can set an ImageView to use the res/drawable/myimage.png resource using setImageResource:

Kotlin

val imageView = findViewById(R.id.myimageview) as ImageView
imageView.setImageResource(R.drawable.myimage)

Java

ImageView imageView = (ImageView) findViewById(R.id.myimageview);

imageView.setImageResource(R.drawable.myimage);

You can also retrieve individual resources using methods in Resources, which you can get an instance of with getResources.

Syntax

Here's the syntax to reference a resource in code:

[<package_name>.]R.<resource_type>.<resource_name>

  • <package_name> is the name of the package in which the resource is located (not required when referencing resources from your own package).
  • <resource_type> is the R subclass for the resource type.
  • <resource_name> is either the resource filename without the extension or the android:name attribute value in the XML element, for simple values.

Use cases

There are many methods that accept a resource ID parameter, and you can retrieve resources using methods in Resources. You can get an instance of Resources using Context.getResources.

Here are some examples of accessing resources in code:

Kotlin

// Load a background for the current screen from a drawable resource.
window.setBackgroundDrawableResource(R.drawable.my_background_image)

// Set the Activity title by getting a string from the Resources object, because
//  this method requires a CharSequence rather than a resource ID.
window.setTitle(resources.getText(R.string.main_title))

// Load a custom layout for the current screen.
setContentView(R.layout.main_screen)

// Set a slide in animation by getting an Animation from the Resources object.
flipper.setInAnimation(AnimationUtils.loadAnimation(this,
        R.anim.hyperspace_in))

// Set the text on a TextView object using a resource ID.
val msgTextView = findViewById(R.id.msg) as TextView
msgTextView.setText(R.string.hello_message)

Java

// Load a background for the current screen from a drawable resource.
getWindow().setBackgroundDrawableResource(R.drawable.my_background_image) ;

// Set the Activity title by getting a string from the Resources object, because
//  this method requires a CharSequence rather than a resource ID.
getWindow().setTitle(getResources().getText(R.string.main_title));

// Load a custom layout for the current screen.
setContentView(R.layout.main_screen);

// Set a slide in animation by getting an Animation from the Resources object.
flipper.setInAnimation(AnimationUtils.loadAnimation(this,
        R.anim.hyperspace_in));

// Set the text on a TextView object using a resource ID.
TextView msgTextView = (TextView) findViewById(R.id.msg);
msgTextView.setText(R.string.hello_message);

Access resources from XML

You can define values for some XML attributes and elements using a reference to an existing resource. You often do this when creating layout files, to supply strings and images for your widgets.

For example, if you add a Button to your layout, use a string resource for the button text:

<Button
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="@string/submit" />

Syntax

Here is the syntax to reference a resource in an XML resource:

@[<package_name>:]<resource_type>/<resource_name>

  • <package_name> is the name of the package in which the resource is located (not required when referencing resources from the same package).
  • <resource_type> is the R subclass for the resource type.
  • <resource_name> is either the resource filename without the extension or the android:name attribute value in the XML element, for simple values.

Use cases

In some cases, you must use a resource for a value in XML, such as to apply a drawable image to a widget, but you can also use a resource in XML any place that accepts a simple value. For example, if you have the following resource file that includes a color resource and a string resource:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <color name="opaque_red">#f00</color>
  <string name="hello">Hello!</string>
</resources>

You can use these resources in the following layout file to set the text color and text string:

<?xml version="1.0" encoding="utf-8"?>
<EditText xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:textColor="@color/opaque_red"
  android:text="@string/hello" />

In this case, you don't need to specify the package name in the resource reference, because the resources are from your own package. To reference a system resource, you need to include the package name, as shown in the following example:

<?xml version="1.0" encoding="utf-8"?>
<EditText xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:textColor="@android:color/secondary_text_dark"
  android:text="@string/hello" />

You can even use resources in XML to create aliases. For example, you can create a drawable resource that is an alias for another drawable resource:

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
  android:src="@drawable/other_drawable" />

This sounds redundant, but can be very useful when using alternative resource. For more information, see the section about creating alias resources.

Reference style attributes

A style attribute resource lets you reference the value of an attribute in the currently applied theme. Referencing a style attribute lets you customize the look of UI elements by styling them to match standard variations supplied by the current theme, instead of supplying a hardcoded value. Referencing a style attribute essentially says, "Use the style that is defined by this attribute in the current theme."

To reference a style attribute, the name syntax is almost identical to the normal resource format, but instead of the "at" symbol (@), use a question mark (?). The resource type portion is optional. So the reference syntax is as follows:

?[<package_name>:][<resource_type>/]<resource_name>

For example, here's how you can reference an attribute to set the text color to match the secondary text color of the system theme:

<EditText id="text"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:textColor="?android:textColorSecondary"
  android:text="@string/hello_world" />

Here, the android:textColor attribute specifies the name of a style attribute in the current theme. Android now uses the value applied to the android:textColorSecondary style attribute as the value for android:textColor in this widget. Because the system resource tool knows that an attribute resource is expected in this context, you don't need to explicitly state the type, which is ?android:attr/textColorSecondary. You can exclude the attr type.

Access original files

While uncommon, you might need to access your original files and directories. If you do, then saving your files in res/ won't work for you, because the only way to read a resource from res/ is with the resource ID. Instead, you can save your resources in the assets/ directory.

Files saved in the assets/ directory are not given a resource ID, so you can't reference them through the R class or from XML resources. Instead, you can query files in the assets/ directory like a normal file system and read raw data using AssetManager.

However, if all you require is the ability to read raw data (such as a video or audio file), then save the file in the res/raw/ directory and read a stream of bytes using openRawResource.

Access platform resources

Android contains a number of standard resources, such as styles, themes, and layouts. To access these resources, qualify your resource reference with the android package name. For example, Android provides a layout resource you can use for list items in a ListAdapter:

Kotlin

listAdapter = ArrayAdapter(this, android.R.layout.simple_list_item_1, myarray)

Java

setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, myarray));

In this example, simple_list_item_1 is a layout resource defined by the platform for items in a ListView. You can use this instead of creating your own layout for list items.

Provide the best device compatibility with resources

For your app to support multiple device configurations, it's very important that you always provide default resources for each type of resource that your app uses.

For example, if your app supports several languages, always include a values/ directory (in which your strings are saved) without a language and region qualifier. If you instead put all your string files in directories that have a language and region qualifier, then your app crashes when run on a device set to a language that your strings don't support.

As long as you provide default values/ resources, then your app runs properly, even if the user doesn't understand the language it presents. It's better than crashing.

Likewise, if you provide different layout resources based on the screen orientation, pick one orientation as your default. For example, instead of providing layout resources in layout-land/ for landscape and layout-port/ for portrait, leave one as the default, such as layout/ for landscape and layout-port/ for portrait.

Providing default resources is important not only because your app might run on a configuration you hadn't anticipated, but also because new versions of Android sometimes add configuration qualifiers that lower versions don't support. If you use a new resource qualifier, but maintain code compatibility with lower versions of Android, then when a lower version of Android runs your app, it crashes if you don't provide default resources, because it can't use the resources named with the new qualifier.

For example, if your minSdkVersion is set to 4, and you qualify all of your drawable resources using night mode (night or notnight, which were added in API level 8), then an API level 4 device can't access your drawable resources and crashes. In this case, you probably want notnight to be your default resources, so exclude that qualifier and put your drawable resources in either drawable/ or drawable-night/.

In short, to provide the best device compatibility, always provide default resources for the resources your app needs to perform properly. Then create alternative resources for specific device configurations using configuration qualifiers.

There is one exception to this rule: If your app's minSdkVersion is 4 or greater, you don't need default drawable resources when you provide alternative drawable resources with the screen density qualifier. Even without default drawable resources, Android can find the best match among the alternative screen densities and scale the bitmaps as necessary. However, for the best experience on all types of devices, provide alternative drawables for all three types of density.