Resource Directory Structure

Android projects organize non-code assets into specific subdirectories within the res/ folder. The build system optimizes these assets, and you access them via unique resource IDs generated in the R class.

Directory	Resource Type
animator/	XML files defining property animations.
anim/	XML files defining tween animations.
color/	XML files defining color state lists.
drawable/	Bitmaps (.png, .9.png, .jpg, .gif) or XML drawables (shapes, layers, selectors).
mipmap/	Launcher icon assets for different densities.
layout/	XML files defining UI structure.
menu/	XML files defining application menus (options, context, submenus).
raw/	Arbitrary files to be opened as a raw input stream (e.g., audio, video).
values/	XML files containing simple values (strings, colors, dimensions, styles). Multiple resources can be defined in one file.
xml/	Arbitrary XML configuration files read at runtime.
font/	Font files (.ttf, .otf) or XML font family definitions.

Note: Do not place resource files directly into the res/ root directory; it will cause a compilation error.

Configuration Qualifiers

Directory names can be modified with configuration qualifiers to allow the system to load the most appropriate resources based on the current device state. The naming convention follows the pattern: <resources_name>-<config_qualifier>.

Configuration	Qualifier Examples	Description
MCC and MNC	mcc310 mcc310-mnc004	Mobile Country Code and Mobile Network Code from the SIM card.
Language and Region	en fr-rCA b+es+419	Two-letter ISO 639-1 language code, optionally followed by a region code. Android 7.0+ supports BCP 47 tags (e.g., b+es+419).
Layout Direction	ldrtl ldltr	ldrtl for right-to-left layouts, ldltr for left-to-right (default).
Smallest Width	sw600dp	The minimum width of the screen available to the layout, regardless of orientation.
Available Width	w720dp	The current minimum available width, changing with orientation.
Available Height	h1024dp	The current minimum available height, changing with orientation.
Screen Size	small normal large xlarge	Generalized screen size buckets based on physical dimensions.
Screen Aspect	long notlong	Widescreen aspect ratio versus non-widescreen.
Screen Shape	round notround	Circular screens (wearables) versus standard rectangular screens.
Wide Color Gamut	widecg nowidecg	Display capability for wide color gamuts (P3, AdobeRGB) or standard sRGB.
Dynamic Range	highdr lowdr	High Dynamic Range (HDR) versus Standard Dynamic Range.
Orientation	port land	Portrait or landscape orientation.
UI Mode	car desk television watch	The device is docked in a car, desk, or presenting on a TV, or is a wearable.
Night Mode	night notnight	Whether night mode is active.
Screen Density	ldpi hdpi xhdpi xxhdpi xxxhdpi nodpi	Density of the screen. nodpi prevents scaling.
Touchscreen	notouch finger	Absence of touch or primary finger interaction.
Keyboard Availability	keysexposed keyshidden	Visibility status of a physical or software keyboard.
Primary Input	nokeys qwerty 12key	Type of hardware keyboard available.
Navigation	navexposed navhidden	Availability of navigation keys.
Navigation Method	nonav dpad trackball	Primary non-touch navigation method.
API Version	v21	Minimum API level supported by the resource.

Handling Configuration Changes

When configuration changes occur (such as screen rotation), the default behavior is to destroy and recreate the Activity. To persist UI data across these changes efficiently, modern Android development relies on using ViewModel objects.

Localization and Locale Detection

To adapt the application to different languages, developers can retrieve the current system locale via the Context configuration.

Java Implementation

Configuration sysConfig = context.getResources().getConfiguration();
Locale primaryLocale = sysConfig.getLocales().get(0);
String userLocale = primaryLocale.getDisplayName();

Kotlin Implementation

val primaryLocale: Locale = context.resources.configuration.locales[0]
val userLocale: String = primaryLocale.displayName

Testing with Pseudolocales

Pseudolocales allow developers to test UI layouts for potential expansion issues caused by string translations. Enable this in your build.gradle file:

android {
    buildTypes {
        debug {
            pseudoLocalesEnabled true
        }
    }
}

Unicode and Internationalization (ICU)

Starting with Android 7.0 (API level 24), the framework utilizes the android.icu library for comprehensive Unicode and internationalization support. Older versions relying on com.ibm.icu should migrate to the native Android package.

Legacy Class	Android ICU Replacement
java.lang.Character	android.icu.lang.UCharacter
java.text.BreakIterator	android.icu.text.BreakIterator
java.text.DecimalFormat	android.icu.text.DecimalFormat
java.util.Calendar	android.icu.util.Calendar
android.text.format.DateFormat	android.icu.text.DateFormat

Note that android.icu does not automatically respect the user's 12/24-hour preference. You must manually apply the skeleton:

boolean is24Hour = android.text.format.DateFormat.is24HourFormat(context);
String timeSkeleton = is24Hour ? "Hm" : "hm";

android.icu.text.DateFormat formatter = android.icu.text.DateFormat.getInstanceForSkeleton(timeSkeleton, Locale.getDefault());
String resultTime = formatter.format(new Date());

val is24Hour = android.text.format.DateFormat.is24HourFormat(context)
val timeSkeleton = if (is24Hour) "Hm" else "hm"

val formatter = android.icu.text.DateFormat.getInstanceForSkeleton(timeSkeleton, Locale.getDefault())
val resultTime = formatter.format(Date())

Transliteration

Android 10 (API level 29) introduced the Transliterator API. This utility converts text from one script to another (e.g., Latin to Cyrillic). Developers should verify available IDs using Transliterator.getAvailableIDs() before usage, as IDs vary by device manufacturer.

Resource Resolution Strategy

The Android runtime attempts to find the most specific resource match. If an exact match is not found (e.g., requesting es-MX when only es-ES exists), it may fall back to a less specific qualifier. If no match is found, it defaults to the resource set without qualifiers.

To improve matching accuracy, especially for region-agnostic languages, use BCP 47 language tags. For instance, move generic Spanish resources to values-b+es+419 (Latin American Spanish) rather than a specific country code. Furthermore, API 24+ allows querying the user's full preferred language list via LocaleList.getDefault() for more granular control.

Animated Vector Drawables

Historically, creating an animated vector drawable required three separate XML files: a vector drawable, an animator, and an animated-vector XML linking them.

Modern Android tooling allows consolidating these into a single XML file using inline resources via the aapt:attr namespace. This reduces file clutter and simplifies asset management.

Consolidated Example (AVD):

<?xml version="1.0" encoding="utf-8"?>
<animated-vector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:aapt="http://schemas.android.com/aapt">

    <!-- Inline Vector Definition -->
    <aapt:attr name="android:drawable">
        <vector
            android:width="100dp"
            android:height="100dp"
            android:viewportWidth="100"
            android:viewportHeight="100">

            <group
                android:name="scaleGroup"
                android:pivotX="50"
                android:pivotY="50">
                <path
                    android:fillColor="#FF5722"
                    android:pathData="M50,50 L50,20 A30,30 0 1,1 50,80 A30,30 0 1,1 50,20 Z" />
            </group>
        </vector>
    </aapt:attr>

    <!-- Inline Animation Target -->
    <target android:name="scaleGroup">
        <aapt:attr name="android:animation">
            <objectAnimator
                android:duration="2000"
                android:propertyName="scaleX"
                android:valueFrom="1"
                android:valueTo="1.5"
                android:valueType="floatType"
                android:repeatCount="-1"
                android:repeatMode="reverse" />
        </aapt:attr>
    </target>
</animated-vector>