Covering window of UIAppDelegate with an overlay make user can't touch on extensions of UIActivityViewController when it's displayed

Question

I'm creating an overlay which will cover all displaying views on screen. This overlay always appears even in case rootViewController changes, pushing or presenting.

My idea is

• Create CustomWindow which is a subclass of UIWindow. After that replacing default window of UIApplication with CustomWindow, create a new rootViewController for my new window.
• In CustomWindow, I have an overlay (is an UIView). Overlay have light gray color with an alpha and every event on overlay will be pass through to below view.
• Whenever CustomWindow add a new subview, i will bring overlay to front. It's make sure overlay will be on the top in every case.

CustomWindow

@implementation CustomWindow

- (instancetype)initWithFrame:(CGRect)frame {
  self = [super initWithFrame:frame];

  if (self) {
    _overlay = [[UIView alloc] initWithFrame:self.bounds];
    _overlay.userInteractionEnabled = NO;
    _overlay.backgroundColor = [UIColor lightGrayColor];
    _overlay.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self addSubview:_overlay];
  }

  return self;
}

- (void)didAddSubview:(UIView *)subview {
  [super didAddSubview:subview];

  [self bringSubviewToFront:_overlay];
}

@end

Everything works fine in every case even when pushing, presenting or changing rootViewController.

Problem

But when i show an UIActivityViewController, I can't click on any extensions which are displayed on UIActivityViewController.

Magically

• When i click outside of UIActivityViewController or click on Cancel Button, UIActivityViewController is dismissed normally.

• If i change color of overlay to clearColor, it works fine too.

My question is

• How can i touch on extensions when i have overlay on window and overlay have a color ?

• If i can't, can anyone tell me why it happens ? It's perfect when you can quote the reason from a document.

I'm pretty sure this doesn't relate to how i initialize UIActivityViewController or the way i show UIActivityViewController.

MORE

I found a problem quite similar to this problem on Android. But i'm not sure because i haven't seen any official document about it from Apple. One more thing is when changing color to clearColor can affect touch. So actually, i don't think they are same.

Answer 1

This is due to a UIRemoveView (private) in the hierarchy. As best I can determine, your app cannot forward events directly to remote views. I suspect this is a security measure to prevent you from presenting the share dialog and automatically sending a touch event to it to do an external action the user didn't request. Remote views don't run in your application's process. The "Copy" button is interacted with across an XPC link.

This all means that if the remote view is covered by one of your views, there's no way (at least that I've found) to interact with it. You have to ensure that you're not covering it.

Actually doing that is simple. The thing that holds the remote view is called a UITransitionView and is used for other OS-level things that you probably shouldn't be covering either. So don't:

- (void)didAddSubview:(UIView *)subview {
    [super didAddSubview:subview];

    if ([subview isKindOfClass:NSClassFromString(@"UITransitionView")]) {
        // To raise it above your overlay;
        // otherwise it's immediately above the view controller (below the overlay)
        [self bringSubviewToFront:subview];
    } else {
        [self bringSubviewToFront:self.overlay];
    }
}

But.... This requires you to talk about UITransitionView in your code. This is both fragile, and possibly a forbidden use of private APIs.

Otherwise you'll have to wrap your UIActivityViewController requests with some call/notification that tells the window not to cover views until we're done (which you'll have to clear in the completion handler).