KVC

@通常,我们都是通过属性的set和get方法来赋值和取值,这里介绍用Key-Value-Coding(KVC)键值编码来给类的属性赋值和取值.

1.基本方式(setValue:forKey:      valueForKey)

//  ---定义一个Student类(.m文件无任何操作)
#import <Foundation/Foundation.h>


@class HMTClass;
@interface HMTStudent : NSObject{

    NSString * _name;
   
    BOOL _test;
    BOOL _isTest;
    BOOL test;
    BOOL isTest;

}

@property (nonatomic,copy)NSString * name;
@property (nonatomic,copy)NSString * sex;
@property (nonatomic,assign)NSInteger age;
@property (nonatomic,strong) HMTClass * hmtClass;

@end

//  ---main文件
HMTStudent * student = [[HMTStudent alloc] init];
    
student.hmtClass = [[HMTClass alloc] init];
student.name = @"humingtao”;     //  set方法赋值
   
//  KVC赋值    
[student setValue:@“mawei is dog" forKey:@"name”];  
[student setValue:@"m" forKey:@"sex"];
[student setValue:@(10) forKey:@"age"];
//  取值    
NSLog(@"%s__%d__|%@",__FUNCTION__,__LINE__,[student valueForKey:@"name"]);

@特别注意:
   我在类里面还定义了4个BOOL值变量,用来验证KVC访问属性键顺序
       [student setValue:@(YES) forKey:@"test”];

       结果是:_test—>_isTest—>test—>isTest

2.键路径访问(用于一个类中属性的属性 setValue:ForKeyPath: forKeyPath)

//  创建一个班级类
@interface HMTClass : NSObject

@property (nonatomic,copy)NSString * name;

@end

然后前面第一点中在Student类中写了一个班级属性hmtClass

HMTClass *hmtClass = [[HMTClass alloc]init];
[hmtClass setValue:@"宇宙一班" forKey:@"name"];
[student setValue:hmtClass forKey:@"hmtClass"];
NSString *hmtClassName = [student valueForKeyPath:@"hmtClass.name"];

//也可以这样存值
[student setValue:@"宇宙一班" forKeyPath:@"hmtClass.name"];
student.hmtClass.name = [student valueForKeyPath:@"hmtClass.name"];

3.自动封装基本数据类型
我们在Student类中添加分数属性 NSInteger number 学号;

#import <Foundation/Foundation.h>  
@class HMTClass;  
@interface HMTStudent : NSObject  
{  
    NSString *_name;  

    NSInteger number;  
}  
@end  

[student setValue:@"100" forKeyPath:@"number"];  
NSString *number = [student valueForKey:@"number"];  
可见用NSString*类型设置的属性值@"100"，而我们的属性是NSInteger类型的，存取都没有问题。

4.操作集合

在Student类中加入数组NSArray,用来表示其他的学生。

#import <Foundation/Foundation.h>  
@class HMTClass;  
@interface HMTStudent : NSObject  
{  
    NSArray *manyStudents;  
}  
@end  
          
Student *student1 = [[HMTStudent alloc]init];  
Student *student2 = [[HMTStudent alloc]init];  
Student *student3 = [[HMTStudent alloc]init];  
[student1 setValue:@"200" forKey:@"number"];  
[student2 setValue:@"300" forKey:@"number"];  
[student3 setValue:@"400" forKey:@"number"];  
NSArray *array = [NSArray arrayWithObjects:student1,student2,student3,nil];  
[student setValue:array forKey:@"manyStudents"];  
NSLog(@"%@",[student valueForKeyPath:@"manyStudents.number"]);  
打印出来是数组(200,300,400)