Apps written in Compose should support accessibility for users with different needs. Accessibility services are used to transform what’s shown on screen to a more fitting format for a user with a specific need. To support accessibility services, apps use APIs in the Android framework to expose semantic information about their UI elements. The Android framework will then inform accessibility services about this semantic information. Each accessibility service can choose how best to describe the app to the user. Android provides several accessibility services, including Talkback and Switch Access.
Semantics
Compose uses semantics properties to pass information to accessibility
services. Semantics properties provide information about UI elements that are
displayed to the user. Most built-in composables like
Text and
Button
fill these semantics properties with information inferred from the composable
and its children. Some modifiers like
toggleable
and
clickable
will also set certain semantics properties. However, sometimes the framework
needs more information to understand how to describe a UI element to the user.
This document describes various situations in which you need to explicitly add extra information to a composable so it can be correctly described to the Android framework. It also explains how to replace the semantics information completely for a given composable. It assumes a basic understanding of accessibility in Android.
Common use cases
To help people with accessibility needs use your app successfully, your app should follow the best practices described on this page.
Consider minimum touch target sizes
Any on-screen element that someone can click, touch, or interact with should be large enough for reliable interaction. When sizing these elements, make sure to set the minimum size to 48dp to correctly follow the Material Design Accessibility Guidelines.
Material components—like
Checkbox,
RadioButton,
Switch,
Slider, and
Surface—set
this minimum size internally, but only when the component can receive user
actions. For example, when a Checkbox has its onCheckedChange parameter set
to a non-null value, it will include padding to have a width and height of at
least 48dp.
@Composable
private fun CheckableCheckbox() {
Checkbox(checked = true, onCheckedChange = {})
}
When the onCheckedChange parameter is set to null, the padding is not included, because the component cannot be interacted with directly.
@Composable
private fun NonClickableCheckbox() {
Checkbox(checked = true, onCheckedChange = null)
}
When implementing selection controls like Switch, RadioButton, or
Checkbox, you typically lift the clickable behavior to a parent container,
set the click callback on the composable to null, and add a toggleable or
selectable modifier to the parent composable.
@Composable
private fun CheckableRow() {
MaterialTheme {
var checked by remember { mutableStateOf(false) }
Row(
Modifier
.toggleable(
value = checked,
role = Role.Checkbox,
onValueChange = { checked = !checked }
)
.padding(16.dp)
.fillMaxWidth()
) {
Text("Option", Modifier.weight(1f))
Checkbox(checked = checked, onCheckedChange = null)
}
}
}
When the size of a clickable composable is smaller than the minimum touch target size, Compose still increases the touch target size. It does so by expanding the touch target size outside of the boundaries of the composable.
In the following example we create a very small clickable Box. The touch
target area is automatically expanded beyond the boundaries of the Box, so
tapping next to the Box still triggers the click event.
@Composable
private fun SmallBox() {
var clicked by remember { mutableStateOf(false) }
Box(
Modifier
.size(100.dp)
.background(if (clicked) Color.DarkGray else Color.LightGray)
) {
Box(
Modifier
.align(Alignment.Center)
.clickable { clicked = !clicked }
.background(Color.Black)
.size(1.dp)
)
}
}
To prevent possible overlap between touch areas of different composables, you
should always aim to use a large enough minimum size for the composable. In our
example that would mean using the sizeIn modifier to set the minimum size for
the inner box:
@Composable
private fun LargeBox() {
var clicked by remember { mutableStateOf(false) }
Box(
Modifier
.size(100.dp)
.background(if (clicked) Color.DarkGray else Color.LightGray)
) {
Box(
Modifier
.align(Alignment.Center)
.clickable { clicked = !clicked }
.background(Color.Black)
.sizeIn(minWidth = 48.dp, minHeight = 48.dp)
)
}
}
Add click labels
You can use a click label to add semantic meaning to the click behavior of a composable. Click labels describe what happens when the user interacts with the composable. Accessibility services use click labels to help describe the app to users with specific needs.
Set the click label by passing a parameter in the
clickable
modifier:
@Composable
private fun ArticleListItem(openArticle: () -> Unit) {
Row(
Modifier.clickable(
// R.string.action_read_article = "read article"
onClickLabel = stringResource(R.string.action_read_article),
onClick = openArticle
)
) {
// ..
}
}
Alternatively, if you don't have access to the clickable modifier, you can set the click label in the semantics modifier:
@Composable
private fun LowLevelClickLabel(openArticle: () -> Boolean) {
// R.string.action_read_article = "read article"
val readArticleLabel = stringResource(R.string.action_read_article)
Canvas(
Modifier.semantics {
onClick(label = readArticleLabel, action = openArticle)
}
) {
// ..
}
}
Describe visual elements
When you define an
Image
or Icon
composable, there is no automatic way for the Android framework to understand
what is being displayed. You need to pass a textual description of the visual
element.
Imagine a screen where the user can share the current page with friends. This screen contains a clickable share icon:
Based on the icon alone, the Android framework can’t figure out how to describe it to a visually impaired user. The Android framework needs an additional textual description of the icon.
The contentDescription parameter is used to describe a visual element. You
should use a localized string, as this will be communicated to the user.
@Composable
private fun ShareButton(onClick: () -> Unit) {
IconButton(onClick = onClick) {
Icon(
imageVector = Icons.Filled.Share,
contentDescription = stringResource(R.string.label_share)
)
}
}
Some visual elements are purely decorative and you might not want to communicate
them to the user. When you set the contentDescription parameter to null,
you indicate to the Android framework that this element does not have associated
actions or state.
@Composable
private fun PostImage(post: Post, modifier: Modifier = Modifier) {
val image = post.imageThumb ?: painterResource(R.drawable.placeholder_1_1)
Image(
painter = image,
// Specify that this image has no semantic meaning
contentDescription = null,
modifier = modifier
.size(40.dp, 40.dp)
.clip(MaterialTheme.shapes.small)
)
}
It is up to you to decide whether a given visual element needs a
contentDescription. Ask yourself if the element conveys information that the
user will need to perform their task. If not, it’s better to leave the
description out.
Merge elements
Accessibility services like Talkback and Switch Access allow users to move focus across elements on the screen. It is important that elements are focused at the right granularity. If every single low-level composable in your screen is focused independently, a user will have to interact a lot to move across the screen. If elements are merged too aggressively, users might not understand which elements belong together.
When you apply a
clickable
modifier to a composable, Compose will automatically merge all elements it
contains. This also holds for
ListItem;
elements within a list item will be merged and accessibility services will view
them as one element.
It is possible to have a set of composables that form a logical group, but that group is not clickable or part of a list item. You’d still want accessibility services to view them as one element. For example, imagine a composable that shows a user’s avatar, their name, and some extra information:
You can tell Compose to merge these elements by using the mergeDescendants
parameter in the semantics modifier. This way, accessibility services will
select only the merged element, and all semantics properties of the descendants
are merged.
@Composable
private fun PostMetadata(metadata: Metadata) {
// Merge elements below for accessibility purposes
Row(modifier = Modifier.semantics(mergeDescendants = true) {}) {
Image(
imageVector = Icons.Filled.AccountCircle,
contentDescription = null // decorative
)
Column {
Text(metadata.author.name)
Text("${metadata.date} • ${metadata.readTimeMinutes} min read")
}
}
}
Accessibility services will now focus on the whole container at once, merging their contents:
Add custom actions
Take a look at the following list item:
When you use a screen reader like Talkback to hear what’s displayed on the screen, it will first select the whole item, and then the bookmark icon.
In a long list, this can become very repetitive. A better approach would be to
define a custom action that allows a user to bookmark the item. Keep in
mind that you will also have to explicitly remove the behavior of the bookmark
icon itself, to make sure it will not be selected by the accessibility service.
This is done with the
clearAndSetSemantics
modifier:
@Composable
private fun PostCardSimple(
/* ... */
isFavorite: Boolean,
onToggleFavorite: () -> Boolean
) {
val actionLabel = stringResource(
if (isFavorite) R.string.unfavorite else R.string.favorite
)
Row(
modifier = Modifier
.clickable(onClick = { /* ... */ })
.semantics {
// Set any explicit semantic properties
customActions = listOf(
CustomAccessibilityAction(actionLabel, onToggleFavorite)
)
}
) {
/* ... */
BookmarkButton(
isBookmarked = isFavorite,
onClick = onToggleFavorite,
// Clear any semantics properties set on this node
modifier = Modifier.clearAndSetSemantics { }
)
}
}
Describe an element’s state
A composable can define a stateDescription for semantics which is used by the Android framework to read out the state that the composable is in. For example, a toggleable composable can be in either a “Checked” or an “Unchecked” state. In some cases, you might want to override the default state description labels that are used by Compose. You can do so by explicitly specifying the state description labels before defining a composable as toggleable:
@Composable
private fun TopicItem(itemTitle: String, selected: Boolean, onToggle: () -> Unit) {
val stateSubscribed = stringResource(R.string.subscribed)
val stateNotSubscribed = stringResource(R.string.not_subscribed)
Row(
modifier = Modifier
.semantics {
// Set any explicit semantic properties
stateDescription = if (selected) stateSubscribed else stateNotSubscribed
}
.toggleable(
value = selected,
onValueChange = { onToggle() }
)
) {
/* ... */
}
}
Define headings
Apps sometimes show a lot of content on one screen, in a scrollable container. For example, a screen could show the full contents of an article that the user is reading:
Users with accessibility needs will have a hard time navigating such a screen. To aid navigation, you can indicate which elements are headings. In the example above, each subsection title could be defined as a heading for accessibility. Some accessibility services, like Talkback, allow users to navigate directly from heading to heading.
In Compose, you indicate that a composable is a heading by defining its semantics property:
@Composable
private fun Subsection(text: String) {
Text(
text = text,
style = MaterialTheme.typography.headlineSmall,
modifier = Modifier.semantics { heading() }
)
}
Automated testing of accessibility properties
When customizing your app’s semantic properties, for example when following the use cases listed above, you can verify correctness and prevent regressions by using automated UI tests.
For example, to test that an element’s click label is set correctly, use the following code:
@Test
fun test() {
composeTestRule
.onNode(nodeMatcher)
.assert(
SemanticsMatcher("onClickLabel is set correctly") {
it.config.getOrNull(SemanticsActions.OnClick)?.label == "My Click Label"
}
)
}
Creating custom low-level composables
A more advanced use case involves replacing certain Material components in your
app with custom versions. In this scenario, it is vital that you keep
accessibility considerations in mind. Say you’re replacing the Material
Checkbox
with your own implementation. It would be really easy to forget to add the
triStateToggleable
modifier, which handles the accessibility properties for this component.
As a rule of thumb, you should look at the implementation of the component in the Material library and mimic any accessibility behavior that you can find. Additionally, make heavy use of Foundation modifiers, as opposed to UI level modifiers, as these include accessibility considerations out of the box. Make sure to test your custom component implementation with multiple accessibility services to verify its behavior.
Learn More
To learn more about supporting accessibility in your Compose code, take the Accessibility in Jetpack Compose codelab.