Question

I’ve read many articles to understand why it’s necessary to use @selector() to refer to a method, but I don’t think that I’m satisfied. When we specify an action for a button, for example, we have to write:

[btn addTarget:self action:@selector(myMethod)];

Why not simply:

[btn addTarget:self action:myMethod];

Please explain the need and reason, and what happens without it.

Answer 1

I have read many articles in order to understand the @selector keyword
but I dstill don’t quite understand its purpose. I just want to ask
why we have @selector.

It all has to do with parsing the C language.

On its own, in an expression like [obj performSelector:someRandomSelector]' the compiler treats someRandomSelector bit as “expand whatever someRandomSelector is — evaluating expressions, dealing with #defines, laying down a symbol for later linking, etc… — and whatever that expansion yields better be a SEL.

Thus, if you were to write [obj performSelector:action]' the compiler would have no way to know the difference between action as a variable containing a potentially volatile selector and action being the actual name of a method on obj.

@selector() solves this by creating a syntactic addition to the language that always evaluates to a constant SEL result.

Historically, Objective-C was originally implemented as a straight up extension to the C preprocessor. All the various @... prefixed additions made that implementation much easier in that basically anything prefixed by an @ was an Objective-Cism.