Fix resource transform callback

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/storage/FileSource.java

@@ -123,9 +123,9 @@ private FileSource(String cachePath, String apkPath) {
    * The callback will be executed on the main thread once for every requested URL.
    * </p>
    *
-   * @param callback the callback to be invoked
+   * @param callback the callback to be invoked or null to reset
    */
-  public native void setResourceTransform(@NonNull final ResourceTransformCallback callback);
+  public native void setResourceTransform(final ResourceTransformCallback callback);
 
   private native void initialize(String accessToken, String cachePath, String apkPath);
 

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

@@ -593,6 +593,20 @@
                 android:value=".activity.FeatureOverviewActivity"/>
         </activity>
 
+        <!-- Storage -->
+        <activity
+            android:name=".activity.storage.UrlTransformActivity"
+            android:description="@string/description_url_transform"
+            android:label="@string/activity_url_transform">
+            <meta-data
+                android:name="@string/category"
+                android:value="@string/category_storage"/>
+            <meta-data
+                android:name="android.support.PARENT_ACTIVITY"
+                android:value=".activity.FeatureOverviewActivity"/>
+        </activity>
+
+
         <!-- For Instrumentation tests -->
         <activity
             android:name=".activity.style.RuntimeStyleTestActivity"

platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/storage/UrlTransformActivity.java

@@ -0,0 +1,102 @@
+package com.mapbox.mapboxsdk.testapp.activity.storage;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+
+import com.mapbox.mapboxsdk.maps.MapView;
+import com.mapbox.mapboxsdk.maps.MapboxMap;
+import com.mapbox.mapboxsdk.maps.OnMapReadyCallback;
+import com.mapbox.mapboxsdk.storage.FileSource;
+import com.mapbox.mapboxsdk.storage.Resource;
+import com.mapbox.mapboxsdk.testapp.R;
+
+import timber.log.Timber;
+
+/**
+ * Test activity showcasing the url transform
+ */
+public class UrlTransformActivity extends AppCompatActivity {
+
+  private MapView mapView;
+
+  /**
+   * Be sure to use an isolated class so the activity is not leaked when
+   * the activity goes out of scope (static class in this case).
+   * <p>
+   * Alternatively, unregister the callback in {@link Activity#onDestroy()}
+   */
+  private static final class Transform implements FileSource.ResourceTransformCallback {
+    @Override
+    public String onURL(@Resource.Kind int kind, String url) {
+      Timber.i("[%s] Could be rewriting %s", Thread.currentThread().getName(), url);
+      return url;
+    }
+  }
+
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    setContentView(R.layout.activity_data_driven_style);
+
+    // Initialize map as normal
+    mapView = (MapView) findViewById(R.id.mapView);
+    mapView.onCreate(savedInstanceState);
+
+    // Get a handle to the file source and set the resource transform
+    FileSource.getInstance(UrlTransformActivity.this).setResourceTransform(new Transform());
+
+    mapView.getMapAsync(new OnMapReadyCallback() {
+      @Override
+      public void onMapReady(MapboxMap map) {
+        Timber.i("Map loaded");
+      }
+    });
+  }
+
+  @Override
+  protected void onStart() {
+    super.onStart();
+    mapView.onStart();
+  }
+
+  @Override
+  protected void onResume() {
+    super.onResume();
+    mapView.onResume();
+  }
+
+  @Override
+  protected void onPause() {
+    super.onPause();
+    mapView.onPause();
+  }
+
+  @Override
+  protected void onStop() {
+    super.onStop();
+    mapView.onStop();
+  }
+
+  @Override
+  protected void onSaveInstanceState(Bundle outState) {
+    super.onSaveInstanceState(outState);
+    mapView.onSaveInstanceState(outState);
+  }
+
+  @Override
+  protected void onDestroy() {
+    super.onDestroy();
+
+    // Example of how to reset the transform callback
+    FileSource.getInstance(UrlTransformActivity.this).setResourceTransform(null);
+
+    mapView.onDestroy();
+  }
+
+  @Override
+  public void onLowMemory() {
+    super.onLowMemory();
+    mapView.onLowMemory();
+  }
+}

platform/android/MapboxGLAndroidSDKTestApp/src/main/res/values/strings.xml

@@ -54,6 +54,7 @@
     <string name="activity_simple_map">Simple Map</string>
     <string name="activity_map_in_dialog">Dialog with map</string>
     <string name="activity_marker_view_rectangle">Marker views in rectangle</string>
+    <string name="activity_url_transform">Url transform</string>
 
     <!--Description-->
     <string name="description_user_location_tracking">Tracks the location of the user</string>
@@ -107,6 +108,7 @@
     <string name="description_map_in_dialog">Display a map inside a dialog fragment</string>
     <string name="description_marker_view_rectangle">Marker Views within a rectangle</string>
     <string name="description_circle_layer">Show bus stops and route in Singapore</string>
+    <string name="description_url_transform">Transform urls on the fly</string>
 
     <!--Categories-->
     <string name="category">category</string>
@@ -122,6 +124,7 @@
     <string name="category_userlocation">User Location</string>
     <string name="category_style">Styling</string>
     <string name="category_features">Features</string>
+    <string name="category_storage">Storage</string>
 
     <!--Actions-->
     <string name="action_remove_polylines">Remove polylines</string>

platform/android/src/file_source.cpp

@@ -46,10 +46,10 @@ void FileSource::setResourceTransform(jni::JNIEnv& env, jni::Object<FileSource::
             // a subsequent call.
             // Note: we're converting it to shared_ptr because this lambda is converted to a std::function,
             // which requires copyability of its captured variables.
-            callback = std::shared_ptr<jni::jobject>(transformCallback.NewGlobalRef(env).release()->Get(), GenericGlobalRefDeleter()),
-            env
+            callback = std::shared_ptr<jni::jobject>(transformCallback.NewGlobalRef(env).release()->Get(), GenericGlobalRefDeleter())
         ](mbgl::Resource::Kind kind, std::string&& url_) {
-            return FileSource::ResourceTransformCallback::onURL(const_cast<jni::JNIEnv&>(env), jni::Object<FileSource::ResourceTransformCallback>(*callback), int(kind), url_);
+            android::UniqueEnv _env = android::AttachEnv();
+            return FileSource::ResourceTransformCallback::onURL(*_env, jni::Object<FileSource::ResourceTransformCallback>(*callback), int(kind), url_);
         });
     } else {
         // Reset the callback