[android] - add convenience method for destroyed state on MapView, ca…

…n be used to determine if an asynchrous result should be set on map.

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java

@@ -425,6 +425,19 @@ public void onDestroy() {
     }
   }
 
+  /**
+   * Returns if the map has been destroyed.
+   * <p>
+   * This method can be used to determine if the result of an asynchronous operation should be set.
+   * </p>
+   *
+   * @return true, if the map has been destroyed
+   */
+  @UiThread
+  public boolean isDestroyed() {
+    return destroyed;
+  }
+
   @Override
   public boolean onTouchEvent(MotionEvent event) {
     if (!isMapInitialized() || !isZoomButtonControllerInitialized() || !isGestureDetectorInitialized()) {

platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/annotation/BulkMarkerActivity.java

@@ -92,7 +92,7 @@ private void onLatLngListLoaded(List<LatLng> latLngs, int amount) {
   }
 
   private void showMarkers(int amount) {
-    if (mapboxMap == null || locations == null) {
+    if (mapboxMap == null || locations == null || mapView.isDestroyed()) {
       return;
     }
 

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

@@ -14,7 +14,6 @@
 import android.view.View;
 import android.widget.TextView;
 import android.widget.Toast;
-
 import com.mapbox.geojson.Feature;
 import com.mapbox.geojson.FeatureCollection;
 import com.mapbox.mapboxsdk.maps.MapView;
@@ -26,14 +25,13 @@
 import com.mapbox.mapboxsdk.style.sources.Source;
 import com.mapbox.mapboxsdk.testapp.R;
 import com.mapbox.mapboxsdk.testapp.utils.ResourceUtils;
+import timber.log.Timber;
 
 import java.io.IOException;
 import java.lang.ref.WeakReference;
 import java.util.HashMap;
 import java.util.List;
 
-import timber.log.Timber;
-
 import static com.mapbox.mapboxsdk.style.expressions.Expression.concat;
 import static com.mapbox.mapboxsdk.style.expressions.Expression.division;
 import static com.mapbox.mapboxsdk.style.expressions.Expression.downcase;
@@ -240,6 +238,10 @@ protected void onPostExecute(FeatureCollection featureCollection) {
   }
 
   public void onDataLoaded(@NonNull FeatureCollection featureCollection) {
+    if (mapView.isDestroyed()) {
+      return;
+    }
+
     // create expressions
     Expression iconImageExpression = string(get(literal(FEATURE_ID)));
     Expression iconSizeExpression = division(number(get(literal(FEATURE_RANK))), literal(2.0f));