KVC explain the underlying principle

KVC is actually the key coding  

1, the assignment fact, two ways 

• setValue: forKey to an object's property value assignment

• Property assignment to a property valueForKey object of: setValue

2, get the value actually two ways

• valueForKey a property value acquisition targets

• Property values ​​valueForKeyPath get a property of an object

@interface Cat : NSObject
@property (nonatomic,copy) NSString *name;
@end

@interface Person : NSObject
@property (nonatomic,assign) int age;
@property (nonatomic, strong) Cat *cat;
@end


  self.p=[[Person alloc]init];
    Cat *cat=[[Cat alloc]init];
    self.p.cat=cat;
    [self.p setValue:@12 forKey:@"age"];
    [self.p setValue:@"猪" forKeyPath:@"cat.name"];
    NSLog(@"--%d--%@",self.p.age,self.p.cat.name);//--12--猪
    
     NSLog(@"--%@--%@",[self.p valueForKey:@"age"],[self.p valueForKeyPath:@"cat.name"]);//--12--猪

3, setValue: forKey: Principle

 

 4, valueForKey: principles

  self.p=[[Person alloc]init];
   [self.p setValue:@12 forKey:@"age"];

#import "Person.h"

@implementation Person
-(void)setAge:(int)age{
    NSLog(@"1");
}
-(void)_setAge:(int)age{
    NSLog(@"2");
}
@end

@interface Person : NSObject
{
    int _age;
    int _isAge;
    int  age;
    int isAge;
}
@end

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@implementation Person
-(int)getAge{
    return 1;
}
-(int)age{
    return 2;
}
-(int)isAge{
    return 3;
}
-(int)_age{
    return 4;
}
@end

.h
@interface Person : NSObject
{
    int _age;
    int _isAge;
    int  age;
    int isAge;
}