MapLibreParticleLab/platform/android/docs/styling/feature-state.md

Feature State

{{ activity_source_note("FeatureStateActivity.kt") }}

This example shows how to use feature-state for interactive styling on Android.

Feature state lets you attach runtime JSON values to individual features, then read those values back inside style expressions. This is useful for interaction-driven UI such as selection, highlighting, or temporary analysis state.

Load US states from a remote GeoJSON source

The example loads the same US states GeoJSON used by the GLFW and iOS demos:

--8<-- "MapLibreAndroidTestApp/src/main/java/org/maplibre/android/testapp/activity/feature/FeatureStateActivity.kt:addStatesLayer"

Style layers with feature-state expressions

The fill color/opacity and border color/width respond to a selected boolean stored in feature state:

• Selected — red fill, higher opacity, thicker red border
• Default — blue fill, semi-transparent, thin blue border

Toggle selection on tap

Tapping a state toggles its selected feature-state key and shows a toast:

--8<-- "MapLibreAndroidTestApp/src/main/java/org/maplibre/android/testapp/activity/feature/FeatureStateActivity.kt:handleMapClick"

Notes

• Use GeoJsonSource.setFeatureState() or VectorSource.setFeatureState() to merge new keys into a feature's state.
• Use getFeatureState() on the source to inspect the current state for one feature.
• Use removeFeatureState() or resetFeatureStates() on the source to clear state.
• For VectorSource, all feature-state methods require a sourceLayerId parameter.
• Feature-state expressions update paint properties, including symbol paint properties such as icon-color, icon-opacity, text-color, and text-opacity.
• Feature-state expressions are not supported in layout properties such as icon-image or text-field.