Add feature state functionality to Android (#4219)

platform/android/MapLibreAndroidTestApp/src/main/AndroidManifest.xml

@@ -831,6 +831,18 @@
                 android:name="android.support.PARENT_ACTIVITY"
                 android:value=".activity.FeatureOverviewActivity" />
         </activity>
+        <activity
+            android:name=".activity.feature.FeatureStateActivity"
+            android:description="@string/description_feature_state"
+            android:exported="true"
+            android:label="@string/activity_feature_state">
+            <meta-data
+                android:name="@string/category"
+                android:value="@string/category_features" />
+            <meta-data
+                android:name="android.support.PARENT_ACTIVITY"
+                android:value=".activity.FeatureOverviewActivity" />
+        </activity>
         <activity
             android:name=".activity.style.SymbolGeneratorActivity"
             android:description="@string/description_symbol_generator"

platform/android/MapLibreAndroidTestApp/src/main/java/org/maplibre/android/testapp/activity/feature/FeatureStateActivity.kt

@@ -0,0 +1,185 @@
+package org.maplibre.android.testapp.activity.feature
+
+import android.graphics.Color
+import android.graphics.PointF
+import android.os.Bundle
+import android.view.View
+import android.widget.Toast
+import androidx.appcompat.app.AppCompatActivity
+import com.google.gson.JsonObject
+import org.maplibre.android.camera.CameraUpdateFactory
+import org.maplibre.android.geometry.LatLng
+import org.maplibre.android.maps.MapLibreMap
+import org.maplibre.android.maps.MapView
+import org.maplibre.android.maps.Style
+import org.maplibre.android.style.expressions.Expression.*
+import org.maplibre.android.style.layers.FillLayer
+import org.maplibre.android.style.layers.LineLayer
+import org.maplibre.android.style.layers.PropertyFactory.fillColor
+import org.maplibre.android.style.layers.PropertyFactory.fillOpacity
+import org.maplibre.android.style.layers.PropertyFactory.lineColor
+import org.maplibre.android.style.layers.PropertyFactory.lineWidth
+import org.maplibre.android.style.sources.GeoJsonSource
+import org.maplibre.android.testapp.R
+import org.maplibre.android.testapp.styles.TestStyles
+import java.net.URI
+
+/**
+ * Test activity showcasing interactive styling with feature state.
+ *
+ * Loads US states from a remote GeoJSON source and uses feature-state
+ * expressions to highlight tapped states.
+ */
+class FeatureStateActivity : AppCompatActivity() {
+    companion object {
+        private const val STATES_SOURCE_ID = "states"
+        private const val FILL_LAYER_ID = "state-fills"
+        private const val LINE_LAYER_ID = "state-borders"
+        private const val STATES_URL =
+            "https://maplibre.org/maplibre-gl-js/docs/assets/us_states.geojson"
+    }
+
+    private lateinit var mapView: MapView
+    private lateinit var maplibreMap: MapLibreMap
+    private lateinit var statesSource: GeoJsonSource
+
+    private val mapClickListener = MapLibreMap.OnMapClickListener { point ->
+        handleMapClick(point)
+    }
+
+    // # --8<-- [start:onCreate]
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_query_features_point)
+
+        mapView = findViewById<View>(R.id.mapView) as MapView
+        mapView.onCreate(savedInstanceState)
+        mapView.getMapAsync { map ->
+            maplibreMap = map
+            maplibreMap.moveCamera(
+                CameraUpdateFactory.newLatLngZoom(LatLng(42.619626, -103.523181), 3.0)
+            )
+            maplibreMap.setStyle(TestStyles.getPredefinedStyleWithFallback("Streets")) { style ->
+                addStatesLayer(style)
+                maplibreMap.addOnMapClickListener(mapClickListener)
+            }
+        }
+    }
+    // # --8<-- [end:onCreate]
+
+    // # --8<-- [start:addStatesLayer]
+    private fun addStatesLayer(style: Style) {
+        val source = GeoJsonSource(STATES_SOURCE_ID, URI(STATES_URL))
+        style.addSource(source)
+        statesSource = source
+
+        val selectedFill = Color.parseColor("#d94d41")
+        val defaultFill = Color.parseColor("#2f7de1")
+        val selectedBorder = Color.parseColor("#8f241f")
+        val defaultBorder = Color.parseColor("#2f7de1")
+
+        style.addLayer(
+            FillLayer(FILL_LAYER_ID, STATES_SOURCE_ID).withProperties(
+                fillColor(
+                    switchCase(
+                        toBool(featureState("selected")),
+                        color(selectedFill),
+                        color(defaultFill)
+                    )
+                ),
+                fillOpacity(
+                    switchCase(
+                        toBool(featureState("selected")),
+                        literal(0.7f),
+                        literal(0.5f)
+                    )
+                )
+            )
+        )
+
+        style.addLayer(
+            LineLayer(LINE_LAYER_ID, STATES_SOURCE_ID).withProperties(
+                lineColor(
+                    switchCase(
+                        toBool(featureState("selected")),
+                        color(selectedBorder),
+                        color(defaultBorder)
+                    )
+                ),
+                lineWidth(
+                    switchCase(
+                        toBool(featureState("selected")),
+                        literal(2.0f),
+                        literal(1.0f)
+                    )
+                )
+            )
+        )
+    }
+    // # --8<-- [end:addStatesLayer]
+
+    // # --8<-- [start:handleMapClick]
+    private fun handleMapClick(point: LatLng): Boolean {
+        val screenPoint: PointF = maplibreMap.projection.toScreenLocation(point)
+        val features = maplibreMap.queryRenderedFeatures(screenPoint, FILL_LAYER_ID)
+        val feature = features.firstOrNull() ?: return false
+        val featureId = feature.id() ?: return false
+
+        val currentState = statesSource.getFeatureState(featureId)
+        val isSelected = currentState
+            ?.get("selected")
+            ?.takeUnless { it.isJsonNull }
+            ?.asBoolean
+            ?: false
+
+        val nextState = JsonObject().apply { addProperty("selected", !isSelected) }
+        statesSource.setFeatureState(featureId, nextState)
+
+        val stateName = feature.getStringProperty("STATE_NAME") ?: "Unknown"
+        Toast.makeText(
+            this,
+            "$stateName ${if (!isSelected) "selected" else "deselected"}",
+            Toast.LENGTH_SHORT
+        ).show()
+        return true
+    }
+    // # --8<-- [end:handleMapClick]
+
+    override fun onStart() {
+        super.onStart()
+        mapView.onStart()
+    }
+
+    override fun onResume() {
+        super.onResume()
+        mapView.onResume()
+    }
+
+    override fun onPause() {
+        super.onPause()
+        mapView.onPause()
+    }
+
+    override fun onStop() {
+        super.onStop()
+        mapView.onStop()
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        mapView.onSaveInstanceState(outState)
+    }
+
+    override fun onDestroy() {
+        super.onDestroy()
+        if (this::maplibreMap.isInitialized) {
+            maplibreMap.removeOnMapClickListener(mapClickListener)
+        }
+        mapView.onDestroy()
+    }
+
+    override fun onLowMemory() {
+        super.onLowMemory()
+        mapView.onLowMemory()
+    }
+}

platform/android/MapLibreAndroidTestApp/src/main/res/raw/test_feature_state_style.json

@@ -0,0 +1,43 @@
+{
+  "version": 8,
+  "center": [0, 0],
+  "zoom": 3,
+  "sources": {
+    "style-source": {
+      "type": "geojson",
+      "data": {
+        "type": "FeatureCollection",
+        "features": [
+          {
+            "type": "Feature",
+            "id": "feature-1",
+            "properties": {},
+            "geometry": {
+              "type": "Point",
+              "coordinates": [0, 0]
+            }
+          }
+        ]
+      }
+    }
+  },
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "paint": {
+        "background-color": "#ffffff"
+      }
+    },
+    {
+      "id": "selected-layer",
+      "type": "circle",
+      "source": "style-source",
+      "filter": ["==", ["feature-state", "selected"], true],
+      "paint": {
+        "circle-radius": 12,
+        "circle-color": "#ff0000"
+      }
+    }
+  ]
+}

platform/android/MapLibreAndroidTestApp/src/main/res/values/descriptions.xml

@@ -50,6 +50,7 @@
     <string name="description_query_rendered_features_box_symbol_count">Count all rendered symbols in box</string>
     <string name="description_query_rendered_features_box_highlight">Highlight buildings in box</string>
     <string name="description_query_source_features">Query source for features</string>
+    <string name="description_feature_state">Toggle feature state and style features interactively</string>
     <string name="description_simple_map">Shows a simple map</string>
     <string name="description_map_change">Logs map change events to Logcat</string>
     <string name="description_visibility_map">Changes visibility of map and view parent</string>

platform/android/MapLibreAndroidTestApp/src/main/res/values/titles.xml

@@ -49,6 +49,7 @@
     <string name="activity_query_rendered_features_box_symbol_count">Count symbols in box</string>
     <string name="activity_query_rendered_features_box_highlight">Highlight features in box</string>
     <string name="activity_query_source_features">Query source features</string>
+    <string name="activity_feature_state">Feature state</string>
     <string name="activity_symbol_layer">Symbols</string>
     <string name="activity_add_sprite">Add Custom Sprite</string>
     <string name="activity_simple_map">Simple Map</string>