Using multiplatform resources in your app

When you've set up the resources for your project, build the project to generate the special Res class which provides access to resources. To regenerate the Res class and all the resource accessors, build the project again or re-import the project in the IDE.

After that, you can use the generated class to access the configured multiplatform resources from your code or from external libraries.

Customizing accessor class generation

You can customize the generated Res class to suit your needs using Gradle settings.

In the compose.resources {} block of the build.gradle.kts file, you can specify several settings that affect the way the Res class is generated for your project. An example configuration looks like this:

compose.resources {
    publicResClass = false
    packageOfResClass = "me.sample.library.resources"
    generateResClass = auto
}

publicResClass set to true makes the generated Res class public. By default, the generated class is internal.
packageOfResClass allows you to assign the generated Res class to a particular package (to access within the code, as well as for isolation in a final artifact). By default, Compose Multiplatform assigns the {group name}.{module name}.generated.resources package to the class.
generateResClass set to always makes the project unconditionally generate the Res class. This may be useful when the resource library is only available transitively. By default, Compose Multiplatform uses the auto value to generate the Res class only if the current project has an explicit implementation or api dependency on the resource library.

Resource usage

Images

You can access drawable resources as simple images, rasterized images or XML vectors. SVG images are supported on all platforms except Android.

To access drawable resources as Painter images, use the painterResource() function:
@Composable fun painterResource(resource: DrawableResource): Painter {...}
The painterResource() function takes a resource path and returns a Painter value. The function works synchronously on all targets except for web. For the web target, it returns an empty Painter for the first recomposition that is replaced with the loaded image in subsequent recompositions.
- painterResource() loads either a BitmapPainter for rasterized image formats, such as .png, .jpg, .bmp, .webp, or a VectorPainter for the Android XML vector drawable format.
- XML vector drawables have the same format as Android, except that they don't support external references to Android resources.
To access drawable resources as an ImageBitmap rasterized image, use the imageResource() function:
@Composable fun imageResource(resource: DrawableResource): ImageBitmap {...}
To access drawable resources as an ImageVector XML vector, use the vectorResource() function:
@Composable fun vectorResource(resource: DrawableResource): ImageVector {...}

Here's an example of how you can access images in your Compose Multiplatform code:

Image(
    painter = painterResource(Res.drawable.my_icon),
    contentDescription = null
)

Strings

Store all string resources in XML files in composeResources/values directories. A static accessor is generated for each item in each file.

Simple strings

To store a simple string, add a <string> element to your XML:

<resources>
    <string name="app_name">My awesome app</string>
    <string name="title">Some title</string>
</resources>

To get string resources as a String, use the following code:

@Composable
fun stringResource(resource: StringResource): String {...}

@Composable
fun stringResource(resource: StringResource, vararg formatArgs: Any): String {...}

For example:

Text(stringResource(Res.string.app_name))

suspend fun getString(resource: StringResource): String

suspend fun getString(resource: StringResource, vararg formatArgs: Any): String

For example:

coroutineScope.launch {
    val appName = getString(Res.string.app_name)
}

You can use special symbols in string resources:

\n — for a new line
\t — for a tab symbol
\uXXXX — for a specific Unicode character

String templates

Currently, arguments have basic support in string resources:

<resources>
    <string name="str_template">Hello, %1$s! You have %2$d new messages.</string>
</resources>

There is no difference between %...s and %...d when using string templates with arguments from composable code, for example:

Text(stringResource(Res.string.str_template, "User_name", 100))

String arrays

You can group related strings into an array and automatically access them as a List<String> object:

<resources>
    <string name="app_name">My awesome app</string>
    <string name="title">Some title</string>
    <string-array name="str_arr">
        <item>item \u2605</item>
        <item>item \u2318</item>
        <item>item \u00BD</item>
    </string-array>
</resources>

To get the corresponding list, use the following code:

@Composable
fun stringArrayResource(resource: StringArrayResource): List<String> {...}

For example:

Text(stringArrayResource(Res.array.str_arr)[0])

suspend fun getStringArray(resource: StringArrayResource): List<String>

For example:

coroutineScope.launch {
    val appName = getStringArray(Res.array.str_arr)
}

Plurals

When your UI displays quantities of something, you might want to support grammatical agreement for different numbers of the same thing (one book, many books, and so on) without creating programmatically unrelated strings.

The concept and base implementation in Compose Multiplatform are the same as for quantity strings on Android. See the Android documentation for more about best practices and nuances of using plurals in your project.

The supported variants are zero, one, two, few, many, and other. Note that not all variants are even considered for every language: for example, zero is ignored for English because it is the same as any other plural except 1. Rely on a language specialist to know what distinctions the language actually insists upon.
It's often possible to avoid quantity strings by using quantity-neutral formulations such as "Books: 1". If this doesn't worsen the user experience,

To define a plural, add a <plurals> element to any .xml file in your composeResources/values directory. A plurals collection is a simple resource referenced using the name attribute (not the name of the XML file). As such, you can combine plurals resources with other simple resources in one XML file under one <resources> element:

<resources>
    <string name="app_name">My awesome app</string>
    <string name="title">Some title</string>
    <plurals name="new_message">
        <item quantity="one">%1$d new message</item>
        <item quantity="other">%1$d new messages</item>
    </plurals>
</resources>

To access a plural as a String, use the following code:

@Composable
fun pluralStringResource(resource: PluralStringResource, quantity: Int): String {...}

@Composable
fun pluralStringResource(resource: PluralStringResource, quantity: Int, vararg formatArgs: Any): String {...}

For example:

Text(pluralStringResource(Res.plurals.new_message, 1, 1))

suspend fun getPluralString(resource: PluralStringResource, quantity: Int): String

suspend fun getPluralString(resource: PluralStringResource, quantity: Int, vararg formatArgs: Any): String

For example:

coroutineScope.launch {
    val appName = getPluralString(Res.plurals.new_message, 1, 1)
}

Fonts

Store custom fonts in the composeResources/font directory as *.ttf or *.otf files.

To load a font as a Font type, use the Font() function:

@Composable
fun Font(
    resource: FontResource,
    weight: FontWeight = FontWeight.Normal,
    style: FontStyle = FontStyle.Normal
): Font

For example:

val fontAwesome = FontFamily(Font(Res.font.font_awesome))

Raw files

To load any raw file as a byte array, use the Res.readBytes(path) function:

suspend fun readBytes(path: String): ByteArray

You can place raw files in the composeResources/files directory and create any hierarchy inside it.

For example, to access raw files, use the following code:

var bytes by remember {
    mutableStateOf(ByteArray(0))
}
LaunchedEffect(Unit) {
    bytes = Res.readBytes("files/myDir/someFile.bin")
}
Text(bytes.decodeToString())

coroutineScope.launch {
    val bytes = Res.readBytes("files/myDir/someFile.bin")
}

Convert byte arrays into images

If the file you are reading is a bitmap (JPEG, PNG, BMP, WEBP) or an XML vector image, you can use the following functions to convert them into ImageBitmap or ImageVector objects suitable for the Image() composable.

Access the raw files as shown in the Raw files section, then pass the result to a composable:

// bytes = Res.readBytes("files/example.png")
Image(bytes.decodeToImageBitmap(), null)

// bytes = Res.readBytes("files/example.xml")
Image(bytes.decodeToImageVector(LocalDensity.current), null)

On every platform except Android, you can also turn an SVG file into a Painter object:

// bytes = Res.readBytes("files/example.svg")
Image(bytes.decodeToSvgPainter(LocalDensity.current), null)

Generated maps for resources and string IDs

For ease of access, Compose Multiplatform also maps resources with string IDs. You can access them by using the filename as the key:

val Res.allDrawableResources: Map<String, DrawableResource>
val Res.allStringResources: Map<String, StringResource>
val Res.allStringArrayResources: Map<String, StringArrayResource>
val Res.allPluralStringResources: Map<String, PluralStringResource>
val Res.allFontResources: Map<String, FontResource>

An example of passing a mapped resource to a composable:

Image(painterResource(Res.allDrawableResources["compose_multiplatform"]!!), null)

Compose Multiplatform resources as Android assets

Starting with Compose Multiplatform 1.7.1, all multiplatform resources are packed into Android assets. This enables Android Studio to generate previews for Compose Multiplatform composables in Android source sets.

Using Multiplatform resources as Android assets also makes possible direct access from WebViews and media player components on Android, since resources can be reached by a simple path, for example Res.getUri("files/index.html").

An example of an Android composable displaying a resource HTML page with a link to a resource image:

// androidMain/kotlin/com/example/webview/App.kt @OptIn(ExperimentalResourceApi::class) @Composable @Preview fun App() { MaterialTheme { val uri = Res.getUri("files/webview/index.html") // Adding a WebView inside AndroidView with layout as full screen. AndroidView(factory = { WebView(it).apply { layoutParams = ViewGroup.LayoutParams( ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT ) } }, update = { it.loadUrl(uri) }) } }

The example works with this simple HTML file:

<html> <header> <title> Cat Resource </title> </header> <body> <img src="cat.jpg"> </body> </html>

Both resource files in this example are located in the commonMain source set:

File structure of the composeResources directory

Interaction with other libraries and resources

Accessing multiplatform resources from external libraries

If you want to process multiplatform resources using other libraries included in your project, you can pass platform-specific file paths to these other APIs. To get a platform-specific path, call the Res.getUri() function with the project path to the resource:

val uri = Res.getUri("files/my_video.mp4")

Now that the uri variable contains the absolute path to the file, any external library can use that path to access the file in a manner that suits it.

For Android-specific uses, multiplatform resources are also packed as Android assets.

Remote files

In the context of the resource library, only files that are part of the application are considered resources.

You can load remote files from the internet using their URL using specialized libraries:

Using Java resources

While you can use Java resources with Compose Multiplatform, they don't benefit from extended features provided by the framework: generated accessors, multimodule support, localization, and so on. Consider transitioning fully to the multiplatform resource library to unlock that potential.

With Compose Multiplatform 1.7.1, the resources API available in the compose.ui package is deprecated. If you still need to work with Java resources, copy the following implementation to your project to ensure that your code works after you upgrade to Compose Multiplatform 1.7.0 or above:

@Composable internal fun painterResource( resourcePath: String ): Painter = when (resourcePath.substringAfterLast(".")) { "svg" -> rememberSvgResource(resourcePath) "xml" -> rememberVectorXmlResource(resourcePath) else -> rememberBitmapResource(resourcePath) } @Composable internal fun rememberBitmapResource(path: String): Painter { return remember(path) { BitmapPainter(readResourceBytes(path).decodeToImageBitmap()) } } @Composable internal fun rememberVectorXmlResource(path: String): Painter { val density = LocalDensity.current val imageVector = remember(density, path) { readResourceBytes(path).decodeToImageVector(density) } return rememberVectorPainter(imageVector) } @Composable internal fun rememberSvgResource(path: String): Painter { val density = LocalDensity.current return remember(density, path) { readResourceBytes(path).decodeToSvgPainter(density) } } private object ResourceLoader private fun readResourceBytes(resourcePath: String) = ResourceLoader.javaClass.classLoader.getResourceAsStream(resourcePath).readAllBytes()

What's next?

Check out the official demo project that shows how resources can be handled in a Compose Multiplatform project targeting iOS, Android, and desktop.

Last modified: 13 November 2024