IOS学习笔记七之KVC和Key路径

发布时间：2023-03-30 11:05:59 所属栏目：教程来源：

导读：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

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
User.h
#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 */

#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];
}

#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 */

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

#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:@"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

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