[darwin] Simplify MGLStyleLayer initialization and pointer management

Similarly to the previous commit, introduce `-[MGLStyleLayer initWithPendingLayer:]`, allowing the base class to track the owned `_pendingSource` pointer and implement `-addToMapView:` and `-removeFromMapView:` without any casts.

Fixes an issue where `-[MGLStyle layerFromMBGLLayer:]` would wind up creating layers whose `_rawLayer` and `_pendingLayer` held different values.

1 files changed, 38 insertions, 5 deletions

diff --git a/platform/darwin/src/MGLStyleLayer.mm b/platform/darwin/src/MGLStyleLayer.mm
index 47f41e0388..c72541526f 100644
--- a/platform/darwin/src/MGLStyleLayer.mm
+++ b/platform/darwin/src/MGLStyleLayer.mm
@@ -1,24 +1,57 @@
 #import "MGLStyleLayer_Private.h"
 #import "MGLMapView_Private.h"
 
+#include <mbgl/map/map.hpp>
 #include <mbgl/style/layer.hpp>
 
 @interface MGLStyleLayer ()
 
-@property (nonatomic) mbgl::style::Layer *rawLayer;
+@property (nonatomic, readonly) mbgl::style::Layer *rawLayer;
 
 @end
 
-@implementation MGLStyleLayer
+@implementation MGLStyleLayer {
+    std::unique_ptr<mbgl::style::Layer> _pendingLayer;
+}
 
-- (instancetype)initWithIdentifier:(NSString *)identifier
-{
+- (instancetype)initWithRawLayer:(mbgl::style::Layer *)rawLayer {
     if (self = [super init]) {
-        _identifier = identifier;
+        _identifier = @(rawLayer->getID().c_str());
+        _rawLayer = rawLayer;
+    }
+    return self;
+}
+
+- (instancetype)initWithPendingLayer:(std::unique_ptr<mbgl::style::Layer>)pendingLayer {
+    if (self = [self initWithRawLayer:pendingLayer.get()]) {
+        _pendingLayer = std::move(pendingLayer);
     }
     return self;
 }
 
+- (void)addToMapView:(MGLMapView *)mapView belowLayer:(MGLStyleLayer *)otherLayer
+{
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
+    if (otherLayer) {
+        const mbgl::optional<std::string> belowLayerId{otherLayer.identifier.UTF8String};
+        mapView.mbglMap->addLayer(std::move(_pendingLayer), belowLayerId);
+    } else {
+        mapView.mbglMap->addLayer(std::move(_pendingLayer));
+    }
+}
+
+- (void)removeFromMapView:(MGLMapView *)mapView
+{
+    if (self.rawLayer == mapView.mbglMap->getLayer(self.identifier.UTF8String)) {
+        _pendingLayer = mapView.mbglMap->removeLayer(self.identifier.UTF8String);
+    }
+}
+
 - (void)setVisible:(BOOL)visible
 {
     MGLAssertStyleLayerIsValid();