I would like a pattern for a nested private class in Objective C.
Requirements are:
Considering the comments, I am simplifying the requirements:
Is it still not possible?
To avoid exposing a method as part of a class's API, we do not declare it within the @interface section but within the @implementation section. Now, a private method like makeActivationSound can no longer be called by another class. A method call from a Jedi class like… [[Lightsaber new] makeActivationSound];
A property is saved in an object, so you can create an object ITYourCustomClass *objectOfYourCustomClass = [[ITYourCustomClass alloc] init]; and setting the properties objectOfYourCustomClass. title = @"something" . Then you can call [objectOfYourCustomClass doSomethingWithTheTitle]; , which is a public object method.
Objective-C has no notion of private classes or private instance variables in a formal declarative fashion.
Instead, visibility in Objective-C is entirely controlled by where you declare something. If it is in a header file, it can be imported by something else. If it is declared in an implementation file, it cannot (reasonably) be imported and, therefore, is effectively private to that compilation unit.
And by "it", I mean pretty much anything that can be declared; class, global, etc...
I.e. if you stick an @interface/@implementation
pair for a class in a .m
file, that class is effectively private to that compilation unit. Of course, without namespaces, make sure that class is uniquely named.
Consider this:
Foo.h:
@interface Foo: NSObject ... public interface @end
Foo.m:
@interface __FooSupportClass: NSObject ... interface here ... @end @implementation __FooSupportClass @end @interface Foo() @property(retain) __FooSupportClass *__fooSupport; @end @implementation Foo @synthesize __fooSupport = fooSupport__; ... etc ... @end
That gives you a private-by-visibility support class only available in your implementation with an instance variable and setter/getter methods on your class that are not visible outside the compilation unit either.
(Note that Objective-C has "instance variables", not "member variables". They are similar, but you'll be better off using the vocabulary of the language.)
Well you can have "semi-hidden" private methods. You can include an interface file that provides extension methods that is in the implementation file and then just implement the methods declared in there. I was curious about this before and asked a similar question.
Proper Objective-C Helper "Wannabe" Private methods?
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