Private methods using Categories in Objective-C: calling super from a subclass
I was reading how to implement private methods in Objective-C (Best way to define private methods for a class in Objective-C) and a question popped up in my mind:
How do you manage to implement protected methods, i.e. private methods that are visible to subclasses?
Suppose I have a MySuperClass with a Category containing all its private methods, and I want to implement a MySubclass overriding or calling super to one of the MySuperClass private methods. Is that possible (using the Categories approach towards implementing private methods)?
Take a look at some of this code, at the bottom there is the overriden method.
// ===========================
// = File: MySuperClass.h
// = Interface for MySuperClass
// ===========================
@interface MySuperClass : Object
...
@end
// ===========================
// = File: MySuperClass.m
// ===========================
#import "MySuperClass.h"
// ==============================开发者_如何转开发===
// = Interface for Private methods
// =================================
@interface MySuperClass (Private)
-(void) privateInstanceMethod;
@end
// =====================================
// = Implementation of Private methods
// =====================================
@implementation MySuperClass (Private)
-(void) privateInstanceMethod
{
//Do something
}
@end
// ================================
// = Implementation for MySuperClass
// ================================
@implementation MySuperClass
...
@end
// ===========================
// = File: MySubClass.h
// = Interface for MySubClass
// ===========================
@interface MySubClass : MySuperClass
...
@end
// ================================
// = Implementation for MySubClass
// ================================
#import MySubClass.h
@implementation MySubClass
//OVERRIDING a Super Private method.
-(void) privateInstanceMethod
{
[super privateInstanceMethod]; //Compiler error, privateInstanceMethod not visible!
//Do something else
}
@end
Hopefully somebody already figured this out.
Cheers!
This GNUStep page describes one approach Section 4.5:
...The bright side of this is it allows you to simulate protected methods as well. For this, the writer of a subclass must be informed in some way about the protected methods, and they will need to put up with the compiler warnings. Alternatively, you could declare the Protected category in a separate interface file (e.g., "PointProtected.h"), and provide this interface file with the understanding that it should only be imported and used by a subclass's interface file.
At Apple, when they build the frameworks the typical pattern is to have a public header (MyClass.h) and a private header (MyClass_private.h), and only copy the public headers into the build product. The .m file will #import both of them, of course.
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