Question

I need that I can use 1 object of NSString to use in all other files
to access 1 variable in all filees

Answer 1

That’s an unclear question.

If I understand correctly you want to have an global NSString* shared by multiple files. In that case, in one of the source files (.m), insert

NSString* my_global_string = @"...";

and in all other source files (or in a common .h), insert

extern NSString* my_global_string;