UIAppearance was not so simple

The UIAppearance protocol appeared in iOS 5 in 2011, in those distant times when Instagram did not have an Android application, and the serial Ned Stark was not yet cut off.

There is enough information, tutorials, articles on this topic, every iOS developer who is a beginner knows how and why to use it, so this article is not about that. I would like to reflect on what is wrong with him, in my opinion, and why Apple is not paying attention to it.

As a small introductory excerpt from the documentation , which has always been, is and should be the main trusted source of information.

There is a window for sending proxy.

To comply with the UIAppearanceContainer protocol, it must be marked with UI_APPEARANCE_SELECTOR

For myself, I understand it this way: if you want to change the default appearance for all objects of the class implementing the UIAppearance , check whether the property is marked with UI_APPEARANCE_SELECTOR and go ahead. Accordingly, if the property is not UI_APPEARANCE_SELECTOR , then this will not work.

But “failing” does not mean “you can’t try,” so I suggest everyone to conduct a simple experiment: open the first project and add the following line to the application:didFinishLaunchingWithOptions: method:

 UIView.appearance().isHidden = true 

Estimate what happens and run.

I, as a bore, would expect possible options:

• Nothing happens;
• nothing happens, but a log like "isHidden is not UI_APPEARANCE_SELECTOR, stupid" falls into the console;
• The application catches a critical error or an assort with a similar message.

But no, everything, including the main application window, becomes hidden. On the one hand, it is even logical - what is written is done. But on the other hand, it looks like undocumented behavior and, as it seems to me, such a rather big hole.

I could still accept the fact that such tricks could be turned only with those properties that affect the appearance, but this can be done with all properties !

For example, adding to the code that other projects use as a third-party library, this is the line that is sometimes called at a random time:

 UITableView.appearance().delegate = nil 

You can reset all delegates to all tables that appear on the screen after executing this code.

Developers will have a lot of fun trying to understand what happened! Surely, you can come up with something even more fun!

I really hope that such things did not go unnoticed by Apple (information on this subject, however, I did not find), and such tricks are revealed somewhere during the automatic assembly check in AppstoreConnect. But I don’t want to check, to be honest.

Such things, guys. I would be glad to discuss if the topic is interesting to someone.

PS Give me back my 2011!