[android] cache location layer IDs in a set instead of a list

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/location/LocationLayerController.java

@@ -5,6 +5,7 @@ import android.graphics.PointF;
 import android.support.annotation.ColorInt;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.support.annotation.VisibleForTesting;
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
@@ -18,7 +19,6 @@ import com.mapbox.mapboxsdk.style.layers.Layer;
 import com.mapbox.mapboxsdk.style.layers.SymbolLayer;
 import com.mapbox.mapboxsdk.style.sources.GeoJsonSource;
 
-import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -70,7 +70,8 @@ final class LocationLayerController {
   private LocationComponentOptions options;
   private final OnRenderModeChangedListener internalRenderModeChangedListener;
 
-  private final List<String> layerMap = new ArrayList<>();
+  @VisibleForTesting
+  final Set<String> layerSet = new HashSet<>();
   private Feature locationFeature;
   private GeoJsonSource locationSource;
 
@@ -112,7 +113,7 @@ final class LocationLayerController {
         removeLayers();
         addLayers(newLayerBelowOption);
         if (isHidden) {
-          for (String layerId : layerMap) {
+          for (String layerId : layerSet) {
             setLayerVisibility(layerId, false);
           }
         }
@@ -193,7 +194,7 @@ final class LocationLayerController {
 
   void hide() {
     isHidden = true;
-    for (String layerId : layerMap) {
+    for (String layerId : layerSet) {
       setLayerVisibility(layerId, false);
     }
   }
@@ -257,14 +258,14 @@ final class LocationLayerController {
 
   private void addLayerToMap(Layer layer, @NonNull String idBelowLayer) {
     style.addLayerBelow(layer, idBelowLayer);
-    layerMap.add(layer.getId());
+    layerSet.add(layer.getId());
   }
 
   private void removeLayers() {
-    for (String layerId : layerMap) {
+    for (String layerId : layerSet) {
       style.removeLayer(layerId);
     }
-    layerMap.clear();
+    layerSet.clear();
   }
 
   private void setBearingProperty(@NonNull String propertyId, float bearing) {
@@ -351,7 +352,7 @@ final class LocationLayerController {
   }
 
   private void styleScaling(@NonNull LocationComponentOptions options) {
-    for (String layerId : layerMap) {
+    for (String layerId : layerSet) {
       Layer layer = style.getLayer(layerId);
       if (layer instanceof SymbolLayer) {
         layer.setProperties(