个人作品网站模板,百度上做网站需要钱吗,wordpress加logo,微网站设计与开发是什么1、KVC介绍
1#xff09;、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#xff1a;为指定属性设置值
valueForKey:属性名 #xff08;得到或者指定属性的值#xff09; 2#xff09;、当设置value为nil的时候、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 */ User.m #import Foundation/Foundation.h
#import User.himplementation User
synthesize name _name;
synthesize pass;
synthesize birth;
-(void) setName:(NSString *)name
{self-_name [NSString stringWithFormat:hello%, name];
}
end KVCPerson.h#ifndef KVCPerson_h
#define KVCPerson_h
#import Foundation/Foundation.h
#import User.hinterface 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.hint 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
在使用key的时候一定要记得先把成员属性的对象进行初始化不然设置无效如下 [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
