[ios] Add annotation container view (#5194)

Add a container view to hold annotations. This gets around a performance
issue with `UIView:addSubview:` where adding views is N^2. It helps
annotation views avoid cutting into callout views when the annotation
views are transformed to be "flat".

1 files changed, 38 insertions, 0 deletions

diff --git a/platform/ios/src/MGLAnnotationContainerView.m b/platform/ios/src/MGLAnnotationContainerView.m
new file mode 100644
index 0000000000..cd9c990ef0
--- /dev/null
+++ b/platform/ios/src/MGLAnnotationContainerView.m
@@ -0,0 +1,38 @@
+#import "MGLAnnotationContainerView.h"
+#import "MGLAnnotationView.h"
+
+@interface MGLAnnotationContainerView ()
+
+@property (nonatomic) NS_MUTABLE_ARRAY_OF(MGLAnnotationView *) *annotationViews;
+
+@end
+
+@implementation MGLAnnotationContainerView
+
+- (instancetype)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self)
+    {
+        _annotationViews = [NSMutableArray array];
+    }
+    return self;
+}
+
++ (instancetype)annotationContainerViewWithAnnotationContainerView:(nonnull MGLAnnotationContainerView *)annotationContainerView
+{
+    MGLAnnotationContainerView *newAnnotationContainerView = [[MGLAnnotationContainerView alloc] initWithFrame:annotationContainerView.frame];
+    [newAnnotationContainerView addSubviews:annotationContainerView.subviews];
+    return newAnnotationContainerView;
+}
+
+- (void)addSubviews:(NS_ARRAY_OF(MGLAnnotationView *) *)subviews
+{
+    for (MGLAnnotationView *view in subviews)
+    {
+        [self addSubview:view];
+        [self.annotationViews addObject:view];
+    }
+}
+
+@end