IOS学习笔记七之KVC和Key路径

1、KVC介绍

1）、KVC是由NSKeyValueCoding协议提供支持最基本的属性和两个方法如下

setValue:属性值  forkey:属性名：为指定属性设置值

valueForKey:属性名   （得到或者指定属性的值）

2）、当设置value为nil的时候，我们需要在类的实现里面重写setNilValueForKey方法，不然会抛出NSInvalidArgumentException

2、key路径介绍

KVC除了操作对象的属性之外，还可以操作对象的“复合属性”，比如类里面的成员变量是对象，然后给这个成员变量的对象进行赋值，就这样简单理解，赋值之前一定要记得把这个对象进行初始化操作

KVC协议中为操作Key路径的方法如下

setValue:forKeyPath:根据Key设置属性值

valueForKeyPath:根据key的路径获取属性值

2、测试简单Demo

      #ifndef User_h
      #define User_h
      #import <Foundation/Foundation.h>
      @interface User : NSObject
      @property (nonatomic) NSString *name;
      @property (nonatomic, strong) NSString *city;
      @property (nonatomic, copy) NSString *add;
      @property NSString *pass;
      @property NSDate *birth;
      @property NSDate *birth1;
      @end
      #endif /* User_h */
  
 

User.m

      #import <Foundation/Foundation.h>
      #import "User.h"
      @implementation User
      @synthesize name = _name;
      @synthesize pass;
      @synthesize  birth;
      -(void) setName:(NSString *)name
      {
       self->_name = [NSString stringWithFormat:@"hello%@", name];
      }
      @end
  
 

      #ifndef KVCPerson_h
      #define KVCPerson_h
      #import <Foundation/Foundation.h>
      #import "User.h"
      @interface KVCPerson : NSObject
      @property (nonatomic, copy) NSString *name;
      @property (nonatomic, copy) NSString *pass;
      @property (nonatomic, copy) NSDate *birth;
      @property (nonatomic) int price;
      @property (nonatomic) User *user;
      @end
      #endif /* KVCPerson_h */
  
 

KVCPerson.m

      #import <Foundation/Foundation.h>
      #import "KVCPerson.h"
      @implementation KVCPerson
      -(void)setNilValueForKey:(id)key
      {
       if ([key isEqualToString:@"price"])
       {
       _price = 0;
       }
       else
       {
       [super setNilValueForKey:key];
       }
      }
      @end
  
 

main.m

      #import <UIKit/UIKit.h>
      #import "AppDelegate.h"
      #import "Person.h"
      #import "Apple.h"
      #import "User.h"
      #import "Args.h"
      #import "KVCPerson.h"
      #import "FKItem.h"
      #import "FKOrder.h"
      int main(int argc, char * argv[]) {
       @autoreleasepool {
       KVCPerson *person = [KVCPerson new];
       [person setValue:@"chenyu" forKey:@"name"];
       [person setValue:@"1234" forKey:@"pass"];
       [person setValue:[NSDate date] forKey:@"birth"];
       NSLog(@"name is %@", [person valueForKey:@"name"]);
       NSLog(@"pass is %@", [person valueForKey:@"pass"]);
       NSLog(@"birth is %@", [person valueForKey:@"birth"]);
       NSLog(@"price is %@", [person valueForKey:@"price"]);
       [person setValue:nil forKey:@"name"];
       [person setValue:nil forKey:@"price"];
       NSLog(@"name is %@", [person valueForKey:@"name"]);
       NSLog(@"pass is %@", [person valueForKey:@"pass"]);
       NSLog(@"birth is %@", [person valueForKey:@"birth"]);
       NSLog(@"price is %@", [person valueForKey:@"price"]);
       [person setValue:[User new] forKeyPath:@"user"];
       //在使用valueForKeyPath之前一定要记得把成员对象进行初始化，不然直接设置无效
       [person setValue:@"hello" forKeyPath:@"user.city"];
       NSLog(@"user.city is%@", [person valueForKeyPath:@"user.city"]);
       }
      }
  
 

3、运行结果

       name is chenyu
       pass is 1234
       birth is Fri Jul  6 22:39:34 2018
       price is 0
       name is (null)
       pass is 1234
       birth is Fri Jul  6 22:39:34 2018
       price is 0
       user.city is hello
   
  

4、总结

如下

       [person setValue:[User new] forKeyPath:@"user"];
       //在使用valueForKeyPath之前一定要记得把成员对象进行初始化，不然直接设置无效
       [person setValue:@"hello" forKeyPath:@"user.city"];
       NSLog(@"user.city is%@", [person valueForKeyPath:@"user.city"]);
  
 

而不是

       [person setValue:@"hello" forKeyPath:@"user.city"];
       NSLog(@"user.city is%@", [person valueForKeyPath:@"user.city"]);
  
 

这样结果会是null

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/80946987