Question

What I’d like to do is separate a category’s methods into private and public methods. The private methods need to be visible outside of that category’s file, but not outside the class.

For instance, let’s say I have the following files:

ClassA.m
ClassA.h // <-- Includes definitions of public category methods
ClassAPrivates.h // <-- Includes definition of private category methods.
ClassA+Render.m

ClassAPrivates.h would look like this:

@interface ClassA()
// private methods here, for use inside ClassA
@end
@interface ClassA(Render)
// the private methods of the Render category.
-(void)privateConfigureDeviceContext;
-(void)privateConfigureBufferSpace;
@end

And ‘ClassA.h’ would look like this:

@interface ClassA : NSObject
// public methods of ClassA
@end
@interface ClassA (Render)
// public methods of category Render
-(void)drawLine;
-(void)drawCircle;
@end

However, XCode complains about duplicate interface for Render. Any workarounds?

Answer 1

No need to create separate categories for private methods.

There are 3 scenarios:

1. ClassA+Render.m accessing the private methods that are defined in the ClassA.m
2. ClassA.m accessing the private methods that are defined in ClassA+Render.m
3. ClassA+Render.m accessing the properties defined in ClassA.m

Note: Though the original poster hasn’t asked for Scenario 3, I thought it might come in handy

Example

ClassA.m defines 2 private methods

• basePrivateMethod1 – This would invoke renderPrivateMethod1
• basePrivateMethod2

ClassA+Render.m defines 2 private methods

• renderPrivateMethod1
• renderPrivateMethod2 – This would invoke basePrivateMethod2

Scenario 1

• In ClassA+Render.m just create an extension and forward declare the methods that you want to use.

ClassA+Render.m

@interface ClassA ()

- (void) basePrivateMethod1; //Just forward declare the method

@end

Scenario 2

• In ClassA+Render.h just declare the methods defined in ClassA+Render.m.
• In ClassA.m just include (#import) ClassA+Render.h
• Pls note, ClassA+Render.h would / should not be used outside of ClassA

ClassA+Render.h

@interface ClassA (Render)
{
    - (void) basePrivateMethod2;
}

Scenario 3

• Pls note – Properties can not be defined / created in the categories
• So create a new category called ClassA+Properties
• In ClassA+Properties.h redeclare all the properties
• In ClassA+Properties.m use @dynamic for all the properties to tell the compiler that the actual definition of these properties is else where
• In ClassA+Render.m include (#import) ClassA+Properties.h, so that all the properties are accessible

ClassA+Properties.h

@interface ClassA (Properties)
{
    @property NSUInteger property1;
    @property NSUInteger property2;
}

ClassA+Properties.m

@interface ClassA (Properties)
{
    @dynamic property1;
    @dynamic property2;
}