[ios, macos] Add text-color support to format expressions. (#14146)

Added the possibility of overriding paint properties inside the format expression.

Added an example of how to create an MGLAttributedExpression object and documented the attributes keys and value types.

Fixed a bug that ignored the font names.

1 files changed, 11 insertions, 2 deletions

diff --git a/platform/darwin/src/MGLAttributedExpression.m b/platform/darwin/src/MGLAttributedExpression.m
index 715f74e42f..000701f7cf 100644
--- a/platform/darwin/src/MGLAttributedExpression.m
+++ b/platform/darwin/src/MGLAttributedExpression.m
@@ -3,11 +3,12 @@
 
 const MGLAttributedExpressionKey MGLFontNamesAttribute = @"text-font";
 const MGLAttributedExpressionKey MGLFontSizeAttribute = @"font-scale";
+const MGLAttributedExpressionKey MGLFontColorAttribute = @"text-color";
 
 @implementation MGLAttributedExpression
 
 - (instancetype)initWithExpression:(NSExpression *)expression {
-    self = [self initWithExpression:expression attributes:nil];
+    self = [self initWithExpression:expression attributes:@{}];
     return self;
 }
 
@@ -28,7 +29,15 @@ const MGLAttributedExpressionKey MGLFontSizeAttribute = @"font-scale";
     return attributedExpression;
 }
 
-- (instancetype)initWithExpression:(NSExpression *)expression attributes:(NSDictionary<MGLAttributedExpressionKey,id> *)attrs {
++ (instancetype)attributedExpression:(NSExpression *)expression attributes:(nonnull NSDictionary<MGLAttributedExpressionKey,id> *)attrs {
+    MGLAttributedExpression *attributedExpression;
+    
+    attributedExpression = [[self alloc] initWithExpression:expression attributes:attrs];
+    
+    return attributedExpression;
+}
+
+- (instancetype)initWithExpression:(NSExpression *)expression attributes:(nonnull NSDictionary<MGLAttributedExpressionKey,id> *)attrs {
     if (self = [super init])
     {
         MGLLogInfo(@"Starting %@ initialization.", NSStringFromClass([self class]));