[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, 5 insertions, 57 deletions

diff --git a/platform/darwin/src/MGLBackgroundStyleLayer.mm b/platform/darwin/src/MGLBackgroundStyleLayer.mm
index 8f416a0ea2..151d4cadaa 100644
--- a/platform/darwin/src/MGLBackgroundStyleLayer.mm
+++ b/platform/darwin/src/MGLBackgroundStyleLayer.mm
@@ -2,35 +2,28 @@
 // Edit platform/darwin/scripts/generate-style-code.js, then run `make darwin-style-code`.
 
 #import "MGLSource.h"
-#import "MGLMapView_Private.h"
 #import "NSPredicate+MGLAdditions.h"
 #import "NSDate+MGLAdditions.h"
 #import "MGLStyleLayer_Private.h"
+#import "MGLForegroundStyleLayer_Private.h"
 #import "MGLStyleValue_Private.h"
 #import "MGLBackgroundStyleLayer.h"
 
-#include <mbgl/map/map.hpp>
+#include <mbgl/style/transition_options.hpp>
 #include <mbgl/style/layers/background_layer.hpp>
 
 @interface MGLBackgroundStyleLayer ()
 
-@property (nonatomic) mbgl::style::BackgroundLayer *rawLayer;
+@property (nonatomic, readonly) mbgl::style::BackgroundLayer *rawLayer;
 
 @end
 
 @implementation MGLBackgroundStyleLayer
-{
-    std::unique_ptr<mbgl::style::BackgroundLayer> _pendingLayer;
-}
 
 - (instancetype)initWithIdentifier:(NSString *)identifier
 {
-    if (self = [super initWithIdentifier:identifier]) {
-        auto layer = std::make_unique<mbgl::style::BackgroundLayer>(identifier.UTF8String);
-        _pendingLayer = std::move(layer);
-        self.rawLayer = _pendingLayer.get();
-    }
-    return self;
+    auto layer = std::make_unique<mbgl::style::BackgroundLayer>(identifier.UTF8String);
+    return self = [super initWithPendingLayer:std::move(layer)];
 }
 
 - (mbgl::style::BackgroundLayer *)rawLayer
@@ -38,51 +31,6 @@
     return (mbgl::style::BackgroundLayer *)super.rawLayer;
 }
 
-- (void)setRawLayer:(mbgl::style::BackgroundLayer *)rawLayer
-{
-    super.rawLayer = rawLayer;
-}
-
-#pragma mark - Adding to and removing from a map view
-
-- (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)) {
-        return;
-    }
-
-    auto removedLayer = mapView.mbglMap->removeLayer(self.identifier.UTF8String);
-    if (!removedLayer) {
-        return;
-    }
-
-    mbgl::style::BackgroundLayer *layer = dynamic_cast<mbgl::style::BackgroundLayer *>(removedLayer.get());
-    if (!layer) {
-        return;
-    }
-
-    removedLayer.release();
-
-    _pendingLayer = std::unique_ptr<mbgl::style::BackgroundLayer>(layer);
-    self.rawLayer = _pendingLayer.get();
-}
-
 #pragma mark - Accessing the Paint Attributes
 
 - (void)setBackgroundColor:(MGLStyleValue<MGLColor *> *)backgroundColor {