[android] layer list accessor + example

platform/android/MapboxGLAndroidSDKTestApp/src/androidTest/java/com/mapbox/mapboxsdk/testapp/style/RuntimeStyleTests.java

@@ -12,6 +12,7 @@ import android.view.View;
 import com.mapbox.mapboxsdk.maps.MapboxMap;
 import com.mapbox.mapboxsdk.style.layers.CannotAddLayerException;
 import com.mapbox.mapboxsdk.style.layers.FillLayer;
+import com.mapbox.mapboxsdk.style.layers.Layer;
 import com.mapbox.mapboxsdk.style.layers.Property;
 import com.mapbox.mapboxsdk.style.layers.PropertyFactory;
 import com.mapbox.mapboxsdk.style.sources.CannotAddSourceException;
@@ -31,9 +32,12 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import java.util.List;
+
 import static android.support.test.espresso.Espresso.onView;
 import static android.support.test.espresso.matcher.ViewMatchers.isDisplayed;
 import static android.support.test.espresso.matcher.ViewMatchers.withId;
+import static junit.framework.Assert.assertTrue;
 import static junit.framework.Assert.fail;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
@@ -55,6 +59,26 @@ public class RuntimeStyleTests {
     Espresso.registerIdlingResources(idlingResource);
   }
 
+  @Test
+  public void testListLayers() {
+    ViewUtils.checkViewIsDisplayed(R.id.mapView);
+    onView(withId(R.id.mapView)).perform(new BaseViewAction() {
+
+      @Override
+      public void perform(UiController uiController, View view) {
+        MapboxMap mapboxMap = rule.getActivity().getMapboxMap();
+
+        List<Layer> layers = mapboxMap.getLayers();
+        assertNotNull(layers);
+        assertTrue(layers.size() > 0);
+        for (Layer layer : layers) {
+          assertNotNull(layer);
+        }
+      }
+
+    });
+  }
+
   @Test
   public void testGetAddRemoveLayer() {
     ViewUtils.checkViewIsDisplayed(R.id.mapView);

platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/RuntimeStyleActivity.java

@@ -40,6 +40,7 @@ import java.io.Reader;
 import java.io.StringWriter;
 import java.io.Writer;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 import timber.log.Timber;
@@ -150,6 +151,9 @@ public class RuntimeStyleActivity extends AppCompatActivity {
   @Override
   public boolean onOptionsItemSelected(MenuItem item) {
     switch (item.getItemId()) {
+      case R.id.action_list_layers:
+        listLayers();
+        return true;
       case R.id.action_water_color:
         setWaterColor();
         return true;
@@ -197,6 +201,16 @@ public class RuntimeStyleActivity extends AppCompatActivity {
     }
   }
 
+  private void listLayers() {
+    List<Layer> layers = mapboxMap.getLayers();
+    StringBuilder builder = new StringBuilder("Layers:");
+    for (Layer layer : layers) {
+      builder.append("\n");
+      builder.append(layer.getId());
+    }
+    Toast.makeText(this, builder.toString(), Toast.LENGTH_LONG).show();
+  }
+
   private void setLayerInvisible() {
     String[] roadLayers = new String[] {"water"};
     for (String roadLayer : roadLayers) {

platform/android/MapboxGLAndroidSDKTestApp/src/main/res/menu/menu_runtime_style.xml

@@ -2,6 +2,10 @@
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:mapbox="http://schemas.android.com/apk/res-auto">
 
+    <item
+        android:id="@+id/action_list_layers"
+        android:title="List all layers in the style"
+        mapbox:showAsAction="never" />
     <item
         android:id="@+id/action_water_color"
         android:title="Color the water"