KVC 的发现

作者: 骑着老鼠虐大象 | 来源:发表于2016-09-09 00:00 被阅读16次

KVC 的发现
iOS原理篇（二）： KVC实现原理
KVC详解
仿写系统KVC的实现
19.iOS底层学习之iOS底层学习之KVC
KVC，KVO
iOS 关于KVC的一些总结（转）
OC语法：KVC的底层实现
iOS 关于KVC的一些总结
KVC的简单使用

废话不多收，直接上代码

.m文件

#import"Object.h"

@interfaceObject()

{

NSString*_objectStr_M;

NSDictionary*_objectDic_M;

NSNumber*_objectNum_M;

}

@property(nonatomic,strong)NSString*objectStr_propertyM;

@property(nonatomic,strong)NSDictionary*objectDic_propertyM;

@property(nonatomic,strong)NSNumber*objectNum_propertyM;

@end

@implementationObject

{

NSString*objectStr_implementation;

NSDictionary*objectDic_implementation;

NSNumber*objectNum_M;

}

-(instancetype)init

{

self=[superinit];

if(self) {

_objectNum_M=@2;

objectNum_M=@1;

objectStr_implementation=@"objectStr_implementation";

_objectStr_M=@"_objectStr_M";

_objectStr_h=@"_objectStr_h";

_objectStr_propertyh=@"__objectStr_propertyh";

_objectStr_propertyM=@"__objectStr_propertyM";

}

returnself;

}

.h文件

@interfaceObject :NSObject

{

NSString*_objectStr_h;

NSDictionary*_objectDic_h;

NSNumber*_objectNum_h;

}

@property(nonatomic,strong)NSString*objectStr_propertyh;

@property(nonatomic,strong)NSDictionary *objectDic_propertyh;

@property(nonatomic,strong)NSNumber*objectNum_propertyh;

@end

测试代码：

Object*obj=[[Objectalloc]init];

if([objvalueForKey:@"_objectNum_M"])

NSLog(@"_objectNum_M is ______%@",[obj valueForKey:@"_objectNum_M"]);

if([objvalueForKey:@"objectNum_M"])

NSLog(@"objectNum_M is *******%@",[obj valueForKey:@"objectNum_M"]);

if([objvalueForKey:@"_objectStr_M"])

NSLog(@"_objectStr_M is %@",[obj valueForKey:@"_objectStr_M"]);

if([objvalueForKey:@"_objectStr_h"])

NSLog(@"_objectStr_h is %@",[obj valueForKey:@"_objectStr_h"]);

if([objvalueForKey:@"_objectStr_propertyh"])

NSLog(@"_objectStr_propertyh is %@",[obj valueForKey:@"_objectStr_propertyh"]);

if([objvalueForKey:@"_objectStr_propertyM"])

NSLog(@"_objectStr_propertyM is %@",[obj valueForKey:@"_objectStr_propertyM"]);

打印结果：

2016-09-08 23:17:17.759 PopMenu[2743:737039] _objectNum_M is ______2

2016-09-08 23:17:17.759 PopMenu[2743:737039] objectNum_M is *******2

2016-09-08 23:17:17.760 PopMenu[2743:737039] _objectStr_M is _objectStr_M

2016-09-08 23:17:17.760 PopMenu[2743:737039] _objectStr_h is _objectStr_h

2016-09-08 23:17:17.760 PopMenu[2743:737039] _objectStr_propertyh is __objectStr_propertyh

2016-09-08 23:17:17.760 PopMenu[2743:737039] _objectStr_propertyM is __objectStr_propertyM

可是这两句出了问题

2016-09-08 23:17:17.759 PopMenu[2743:737039] _objectNum_M is ______2

2016-09-08 23:17:17.759 PopMenu[2743:737039] objectNum_M is *******2

一开始猜想是_objectNum_M 系统认为是同一变量，但编译器不报错，于是加了一句

这就证明 KVC可以获取所有成员变量和属性的指针

if([objvalueForKey:@"objectStr_implementation"])

NSLog(@"objectStr_implementation is %@",[objvalueForKey:@"objectStr_implementation"]);

发现 2016-09-08 23:17:17.759 PopMenu[2743:737039] objectStr_implementation is objectStr_implementation

猜想错误，于是又猜系统认为_objectNum_M ，objectNum_M是同一变量，于是交换_objectNum_M，objectNum_M 在＋（void）init方法里的赋值顺序，结果还是一样，于是又猜，可能是 _objectNum_M 声明interfaceObject()，objectNum_M 声明在implementationObject里面，优先级不一样，可是结果还是一样，这就证明系统在kvc取值时，_XXX 变量优先级>XXX 变量。这个测试还证明了KVC 权限很高，可以取所有成员和属性的指针。如果用下面这种方式声名，则不能访问：