What Are Semantics?
A metadata layer that describes what a UI element means or does, not just how it looks.
- Drives both accessibility (TalkBack, screen readers) and testing tooling
- Makes UI elements more meaningful and testable
Semantics Tree
- Parallel to the composition tree
- Each “node” holds properties like text, role, state, and custom actions
- Built-in components (Text, Icon, Switch) automatically populate common properties
How Tests Use Semantics
Locate nodes by property
val switchMatcher = SemanticsMatcher.expectValue(
SemanticsProperties.Role, Role.Switch
)
composeTestRule.onNode(switchMatcher)
.performClick()
.assertIsOff()
- Assert state (checked/unchecked, enabled/disabled, content matches)
- Perform interactions (click, swipe, custom semantic actions)
Why It Matters
Testability:
- Find elements by purpose (role, description) rather than view IDs or hierarchy
- Results in stable, maintainable tests that don’t break if you refactor layout
Accessibility:
- Ensures assistive services can navigate and announce the UI meaningfully
- Aligns test coverage with real-world user interactions
Custom Semantics
For custom or low-level components, add semantics manually:
@Composable
fun Subsection(text: String) {
Text(
text = text,
style = MaterialTheme.typography.headlineSmall,
modifier = Modifier.semantics { heading() }
)
}
Use Modifier.semantics { … }
, clearAndSetSemantics { … }
, or merging strategies to tailor the semantics tree.
Inspection & Debugging
Print the semantics tree to log or view in Layout Inspector:
composeTestRule.onRoot(useUnmergedTree = true)
.printToLog("SEMANTICS")
Switch between merged/unmerged views to verify how props combine.
References
Related Articles
To learn more about Jetpack Compose and Android development:
- Jetpack Compose: Architecture - Understand the layered architecture of Compose
- Jetpack Compose: Composition Phase - Learn about UI rendering and state management
- Jetpack Compose: Custom Modifiers - Discover how to create reusable UI patterns
- Kotlin Coroutines: Dispatchers - Learn about managing background tasks in your Compose app