[ios, macos] Make source ownership consistent and GeoJSON content properties writable

Use common initialization logic to create an unique pointer to an mbgl
source object, up front, when a MGL source is created. Keep a raw
pointer to the unique pointer that is pointed at the mbgl source
instance when a MGL source is created or when a MGL source is
obtained by identifier from MGLStyle. Once the transfer of ownership of the 
mbgl source takes place, the unique ptr is null. The raw pointer can be used 
internally for future work that involves mutating the source.

This also changes the URL, features, and geoJSONData content 
properties for MGLGeoJSON source to be writable. If they are set with
valid data after a source has been added to the map then the map will
update to reflect the new data.

1 files changed, 20 insertions, 2 deletions

diff --git a/platform/darwin/src/MGLVectorSource.mm b/platform/darwin/src/MGLVectorSource.mm
index 3597812359..995565419f 100644
--- a/platform/darwin/src/MGLVectorSource.mm
+++ b/platform/darwin/src/MGLVectorSource.mm
@@ -1,12 +1,22 @@
 #import "MGLVectorSource.h"
 
+#import "MGLMapView_Private.h"
 #import "MGLSource_Private.h"
 #import "MGLTileSet_Private.h"
 #import "NSURL+MGLAdditions.h"
 
 #include <mbgl/style/sources/vector_source.hpp>
 
+@interface MGLVectorSource ()
+
+@property (nonatomic) mbgl::style::VectorSource *rawSource;
+
+@end
+
 @implementation MGLVectorSource
+{
+    std::unique_ptr<mbgl::style::VectorSource> _pendingSource;
+}
 
 static NSString *MGLVectorSourceType   = @"vector";
 
@@ -15,6 +25,7 @@ static NSString *MGLVectorSourceType   = @"vector";
     if (self = [super initWithIdentifier:identifier])
     {
         _URL = url;
+        [self commonInit];
     }
     return self;
 }
@@ -24,11 +35,12 @@ static NSString *MGLVectorSourceType   = @"vector";
     if (self = [super initWithIdentifier:identifier])
     {
         _tileSet = tileSet;
+        [self commonInit];
     }
     return self;
 }
 
-- (std::unique_ptr<mbgl::style::Source>)mbglSource
+- (void)commonInit
 {
     std::unique_ptr<mbgl::style::VectorSource> source;
     
@@ -43,7 +55,13 @@ static NSString *MGLVectorSourceType   = @"vector";
                                                              self.tileSet.mbglTileset);
     }
     
-    return std::move(source);
+    _pendingSource = std::move(source);
+    self.rawSource = _pendingSource.get();
+}
+
+- (void)addToMapView:(MGLMapView *)mapView
+{
+    mapView.mbglMap->addSource(std::move(_pendingSource));
 }
 
 @end