Objective-C - 私有(private) vs protected vs 公共(public)

Question

我希望在 Objective-C 中编程时，就类成员如何私有(private)、 protected 和公共(public)如何工作 - 我想我知道其中的区别(我已经在我的父类 Person 中添加了一些关于相同)，但是当我尝试通过子类访问父类的私有(private) ivar/成员时编译器没有提示这一事实现在让我感到困惑。

这是我的父类:

/*
 Person.h
*/

#import <Foundation/Foundation.h>

@interface Person : NSObject 
{
    //We can also define class members/iVars that are of type private
    //This means they can only be accessed by the member functions
    //of the class defining them and not subclasses
    @private
    int yob;    

    //We can also define class members/iVars that are of type public
    //Public members can be accessed directly
    @public
    bool alive;

    //By default class members/iVars are of type protected
    //This means they can only be accessed by a class's own
    //member functions and subclasses of the class and typically
    //also by friend functions of the class and the subclass
    //We can explicitly define members to be protected using the
    //@protected keyword

    @protected
    int age;
    float height;   

}
@property int age;
@property float height;
@property int yob;
@property bool alive;

@end

这是我的派生类 Man:

    /*
     Man - Subclass of Person
    */

    #import <Foundation/Foundation.h>
    #import "Person.h"

    @interface Man : Person
    {
        //iVar for Man
        float mWeight;
    }
    @property float mWeight;

    @end

最后，这是主要的:

#import <Foundation/Foundation.h>
#import "Person.h"
#import "Man.h"

    int main (int argc, const char * argv[]) 
        {
            NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

            //Create a Person object
            Person * aPerson = [[Person alloc]init];

            //Create a Man object
            Man * aMan = [[Man alloc]init];

            //Let's attempt to modify our Person class members
            aPerson.height = 5.11; //Protected
            aPerson.age = 21; //Protected
            aPerson.yob = 2010; //Private
            aPerson.alive = YES; //Public

            //Let's now attempt to modify the same members via our
            //derived class Man - in theory, the private members should
            //not be accessible by the derived class man
            aMan.height = 6; //Protected
            aMan.age = 26; //Protected
            aMan.yob = 2011; //Private
            aMan.alive = YES; //Public
            aMan.mWeight = 190; //Protected member of Man Class

            [pool drain];
            return 0;
        }

编译器不应该提示我为什么尝试访问上面的 aMan.yob 吗？或者通过使用@property 和@synthesize(即setter 和getter 方法)，我是否基本上使该成员受到保护，因此子类可以访问？

Answer 1

通常的技巧是在 .m 文件中创建一个类扩展名，并将您的私有(private)/ protected 属性放在那里而不是在标题中。

//Person.m

@interface Person()

@property float height

@end

这隐藏了“高度”属性

另一个技巧是如果你想创建一个只读属性是在标题中声明它作为

@property(readonly) int myproperty

但在类扩展中作为 readwrite 允许您的 .m 使用 getter/setter 修改值

@property(readwrite) int myproperty