Allow initializing MLNMapView with style json (#3240)

Co-authored-by: Yingfang <junew@microsoft.com>
Co-authored-by: Bart Louwers <bart@emeel.net>

platform/ios/src/MLNMapView.h

@@ -207,6 +207,18 @@ MLN_EXPORT
  */
 - (instancetype)initWithFrame:(CGRect)frame styleURL:(nullable NSURL *)styleURL;
 
+/**
+ * Initializes and returns a newly allocated map view with the specified frame
+ * and style JSON.
+ *
+ * @param frame The frame for the view, measured in points.
+ * @param styleJSON JSON string of the map style to display. The JSON must conform to the
+ *        <a href="https://maplibre.org/maplibre-style-spec/">MapLibre Style Specification</a>.
+ *        Specify `nil` for the default style.
+ * @return An initialized map view.
+ */
+- (instancetype)initWithFrame:(CGRect)frame styleJSON:(NSString *)styleJSON;
+
 // MARK: Accessing the Delegate
 
 /**
@@ -253,6 +265,20 @@ MLN_EXPORT
  */
 @property (nonatomic, null_resettable) NSURL *styleURL;
 
+/**
+ * The style JSON representation of the map.
+ *
+ * Setting this property results in an asynchronous style change. If you wish to know when the style
+ * change is complete, observe the ``MLNMapViewDelegate/mapView:didFinishLoadingStyle:`` method
+ * on ``MLNMapViewDelegate``.
+ *
+ * The JSON must conform to the
+ * <a href="https://maplibre.org/maplibre-style-spec/">MapLibre Style Specification</a>.
+ *
+ * @throws NSInvalidArgumentException if styleJSON is nil or invalid JSON
+ */
+@property (nonatomic, copy) NSString *styleJSON;
+
 /**
  Reloads the style.
 

platform/ios/src/MLNMapView.mm

@@ -424,6 +424,7 @@ public:
 @property (nonatomic, copy) MLNMapCamera *residualCamera;
 @property (nonatomic) MLNMapDebugMaskOptions residualDebugMask;
 @property (nonatomic, copy) NSURL *residualStyleURL;
+@property (nonatomic, copy, nullable) NSString *initialStyleJSON;
 
 /// Tilt gesture recognizer helper
 @property (nonatomic, assign) CGPoint dragGestureMiddlePoint;
@@ -522,6 +523,20 @@ public:
     return self;
 }
 
+- (instancetype)initWithFrame:(CGRect)frame styleJSON:(NSString *)styleJSON
+{
+    if (self = [super initWithFrame:frame])
+    {
+        MLNLogInfo(@"Starting %@ initialization.", NSStringFromClass([self class]));
+        MLNLogDebug(@"Initializing frame: %@ styleJSON: %@", NSStringFromCGRect(frame), styleJSON);
+        [self commonInit];
+        self.styleJSON = styleJSON;
+        _initialStyleJSON = [styleJSON copy];
+        MLNLogInfo(@"Finalizing %@ initialization.", NSStringFromClass([self class]));
+    }
+    return self;
+}
+
 - (instancetype)initWithCoder:(nonnull NSCoder *)decoder
 {
     if (self = [super initWithCoder:decoder])
@@ -552,6 +567,11 @@ public:
         return self.residualStyleURL;
     }
 
+    if (self.mbglMap.getStyle().getJSON().length() > 0 &&
+        self.mbglMap.getStyle().getURL().empty()) {
+        return [NSURL URLWithString:@"local://style.json"];
+    }
+
     NSString *styleURLString = @(self.mbglMap.getStyle().getURL().c_str()).mgl_stringOrNilIfEmpty;
     MLNAssert(styleURLString, @"Invalid style URL string %@", styleURLString);
     return styleURLString ? [NSURL URLWithString:styleURLString] : nil;
@@ -569,6 +589,16 @@ public:
     self.mbglMap.getStyle().loadURL([[styleURL absoluteString] UTF8String]);
 }
 
+- (NSString *)styleJSON {
+    return self.style.styleJSON;
+}
+
+- (void)setStyleJSON:(NSString *)styleJSON {
+    // Reset style and load new JSON
+    self.style = nil;
+    self.mbglMap.getStyle().loadJSON([styleJSON UTF8String]);
+}
+
 - (IBAction)reloadStyle:(__unused id)sender {
     MLNLogInfo(@"Reloading style.");
     NSURL *styleURL = self.styleURL;
@@ -890,7 +920,9 @@ public:
     self.terminated = YES;
     self.residualCamera = self.camera;
     self.residualDebugMask = self.debugMask;
-    self.residualStyleURL = self.styleURL;
+    if (!_initialStyleJSON) {
+        self.residualStyleURL = self.styleURL;
+    }
 
     // Tear down C++ objects, insuring worker threads correctly terminate.
     // Because of how _mbglMap is constructed, we need to destroy it first.