Frontmost visible UIView is not receiving touch, why?

Question

Consider the following view hierarchy

• self.view
  • self.transformedView (z-transform=10, index 0)
  • self.ordinaryView (z-transform=0, index 1)

Put to life by this code

@interface AGSTransformedView : UIView
@end
@implementation AGSTransformedView

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"The transformed view is receiving touch");
    [super touchesBegan:touches withEvent:event];
}

@end


@interface AGSOrdinaryView : UIView
@end
@implementation AGSOrdinaryView

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"The ordinary view is receiving touch");
    [super touchesBegan:touches withEvent:event];
}

@end

@interface AGSViewController ()

@end

@implementation AGSViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    AGSTransformedView *transformed = [[AGSTransformedView alloc] initWithFrame:self.view.bounds];
    transformed.layer.transform = CATransform3DMakeTranslation(0, 0, 10);
    transformed.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:transformed];

    AGSOrdinaryView *ordinary = [[AGSOrdinaryView alloc] initWithFrame:self.view.bounds];
    ordinary.backgroundColor = [UIColor blueColor];
    [self.view addSubview:ordinary];
}

@end

When tapping on the screen I'm seeing this in my console

The ordinary view is receiving touch

On screen I'm only seeing the yellow-colored view (the transform view).

Why doesen't the frontmost visible view receive the touches?

Answer 1

It seems like UIKit only respects the view-hierarchy when determining which view should be the receiver of touches. I have yet to find documentation for this.