IOS中实例的权限控制

@public、@protected、@private的使用

　　　　在OC中声明一个类的时候，可以使用上面 @public、@protected、@private三个关键字声明实例的权限，例如下面的代码：

#import 

@interface Person : NSObject
{
@public
    NSString *_height;
@protected
    NSString *_weight;
@private
    NSString *_wife;
}

@end



@interface Person ()
{
    @public
    NSString *_name;
    @protected
    NSString *_sex;
    @private
    NSString *_phoneNO;
}

- (void)publicMethod;

@end

@implementation Person


- (instancetype)init
{
    if(self = [super init])
    {
        _height = @"1.8m";
        _weight = @"65Kg";
        _wife = @"none";
        _name = @"zhangSan";
        _sex  = @"man";
        _phoneNO = @"1122334455";
    }
    return self;
}

- (void)publicMethod
{
    
}

@end

　　在.h文件中定义了三个实例，这三个实例的权限和public、protected、private相对应，对于一个Person类型的对象p，_name在任何地方都是可以访问的，_sex只能在Person

的子类中访问，_wife只能自己内部访问。在.m文件中定义的三个实例也与public、protected、private相对应，需要注意的是，在其它文件中定义的Person类型的对象p，都不能访问到这三个实例，只有在.m文件内部，public、protected、private才会起到对应的作用。实际上OC中实例的权限控制只是编译时的一种权限限制，在OC runtime的类结构中，实例变量是不存在权限控制的，同样类方法、实例方法也不存在权限控制。

对于KVC来说，无论实例是哪种权限都是可以轻松访问到的，如下面的代码：

 @interface Student : Person

@end


@implementation Student


+ (void)testProtected
{
    Person *p = [Person new];
    NSLog(@"%@",p->_height);
    NSLog(@"%@",p->_weight);
}

- (NSString *)description
{
    Person *p = [Person new];
    NSLog(@"%@",p->_height);
    NSLog(@"%@",p->_weight);
//    NSLog(@"%@",p->_wife);
//    [p publicMethod];
//    [self publicMethod];
    //return [NSString stringWithFormat:@"name == %@\nsex == %@\nphone == %@",_name, _sex,_phoneNO]
//    return [NSString stringWithFormat:@"name == %@\nsex == %@",_name, _sex];
//    return [NSString stringWithFormat:@"%@ , %@ , %@",_height , _weight ,_wife];
    return [NSString stringWithFormat:@"%@ , %@",_height , _weight];
    
}

@end

KVC访问：

#import "Other.h"
#import "Person.h"

@interface Other : NSObject

- (void)testProtected;

- (void)testKVC;

@end


@implementation Other

- (void)testProtected
{
    Person *p = [Person new];
    NSLog(@"%@",p->_height);
//    NSLog(@"%@",p->_weight);
}

- (void)testKVC
{
    Person *p = [Person new];
    NSLog(@"%@",[p valueForKey:@"_name"]);
    NSLog(@"%@",[p valueForKey:@"_sex"]);
    NSLog(@"%@",[p valueForKey:@"_phoneNO"]);

    NSLog(@"%@",[p valueForKey:@"_wife"]);

}

@end

实际KVC读取一个实例变量：

- (id)valueForKey: (NSString*)key
{
    if (!key) {
        id value = [self valueForUndefinedKey:nil];
        return value;
    }

    const char *keyCString = [key UTF8String];
    SEL sel = sel_getUid(keyCString);

    // FIXME: getKey, _getKey, isKey, _isKey are missing

    if ([self respondsToSelector:sel]) {
        id value = [self _wrapReturnValueForSelector:sel];
        return value;
    }

    size_t keyCStringLength = strlen(keyCString);
    char *selBuffer = __builtin_alloca(keyCStringLength + 5);

    char *keyname = __builtin_alloca(keyCStringLength + 1);
    strcpy(keyname, keyCString);

    #define TRY_FORMAT(format)\
            sprintf(selBuffer, format, keyname);\
            sel = sel_getUid(selBuffer);\
            if ([self respondsToSelector:sel]) {\
                id value = [self _wrapReturnValueForSelector:sel];\
                return value;\
            }
    TRY_FORMAT("_%s");
    keyname[0] = toupper(keyname[0]);
    TRY_FORMAT("is%s");
    TRY_FORMAT("_is%s");
//    TRY_FORMAT("get%s");
//    TRY_FORMAT("_get%s");
    #undef TRY_FORMAT

    if ([isa accessInstanceVariablesDirectly]) {
        sprintf(selBuffer, "_%s", keyCString);
        sel = sel_getUid(selBuffer);

        if ([self respondsToSelector:sel]) {
            id value = [self _wrapReturnValueForSelector:sel];
            return value;
        }


        Ivar ivar = class_getInstanceVariable(isa, selBuffer);
        if (!ivar) {
            ivar = class_getInstanceVariable(isa, keyCString);
        }

        if (ivar) {
            id value = [self _wrapValue:(void*)self + ivar_getOffset(ivar) ofType:ivar_getTypeEncoding(ivar)];
            return value;
        }

    }

    id value = [self valueForUndefinedKey:key];
    return value;
}

IOS开发问题积累 Objetice-Cpublic、pro

IOS中实例的权限控制

相关

标签