in Objective-C, how to access private property fro

问题:

I want to access private property of a class from its category.

But to access private property, I have to redeclare the same private property in category.
If I don't redeclare, I get a compile error, Property '<property name>' not found on object of type '<class name> *'.

Is this correct way to access private property of class from category?
And are there better ways to do this?

The following code is the code which private property is redeclared in category:

ClassA.h

@interface ClassA : NSObject
-(void)method1;
@end

ClassA.m

#import "ClassA.h"

// private property
@interface ClassA()
@property (nonatomic) NSString *s;
@end

@implementation ClassA
@synthesize s;

-(void)method1
{
    self.s = @"a";
    NSLog(@"%@", [NSString stringWithFormat:@"%@ - method1", self.s]);
}
@end

ClassA+Category.h

#import "ClassA.h"

@interface ClassA(Category)
-(void)method2;
@end

ClassA+Category.m

#import "ClassA+Category.h"

// redeclare private property
@interface ClassA()
@property(nonatomic) NSString *s;
@end

@implementation ClassA(Category)

-(void)method2
{
    NSLog(@"%@", [NSString stringWithFormat:@"%@ - method2", self.s]);
}
@end

Is is good way to create a file(ClassA+Private.m) for private property and import it from ClassA.m and ClassA+Category.m:

ClassA+Private.m

@interface ClassA()
@property(nonatomic) NSString *s;
@end

回答1:

The best way to solve this is to create ClassA+Private.h and import it in ClassA.m and Category.m. Mind the h at the end, you only need to declare your private properties and methods there, the definition is better kept in ClassA.m.