[core, android] Factor JSON string conversions

This adds a `convertJSON` template, to be used like:

   Error error
   optional<Foo> foo = convertJSON<Foo>(string, error);

Internally, it parses the string with RapidJSON and then calls `convert<Foo>(parsed, error)`.

While here, rationalize GeoJSON converters and fix error handling for Tileset conversion in OfflineDownload.

1 files changed, 2 insertions, 12 deletions

diff --git a/platform/android/src/style/conversion/geojson.hpp b/platform/android/src/style/conversion/geojson.hpp
index 32a473b092..748fe7361e 100644
--- a/platform/android/src/style/conversion/geojson.hpp
+++ b/platform/android/src/style/conversion/geojson.hpp
@@ -10,25 +10,15 @@ namespace style {
 namespace conversion {
 
 template <>
-optional<GeoJSON> convertGeoJSON(const mbgl::android::Value& value, Error& error) {
-
+optional<GeoJSON> Converter<GeoJSON>::operator()(const mbgl::android::Value& value, Error& error) const {
     if(value.isNull() || !value.isString()) {
         error = { "no json data found" };
         return {};
     }
 
-    return convertGeoJSON(value.toString(), error);
+    return convert<GeoJSON>(value.toString(), error);
 }
 
-template <>
-struct Converter<GeoJSON> {
-
-    optional<GeoJSON> operator()(const mbgl::android::Value& value, Error& error) const {
-        return convertGeoJSON(value, error);
-    }
-
-};
-
 } // namespace conversion
 } // namespace style
 } // namespace mbgl