1、KVC介紹

1）、KVC是由NSKeyValueCoding協議提供支持最基本的屬性和兩個方法如下

setValue:屬性值? forkey:屬性名：為指定屬性設置值

valueForKey:屬性名 ? （得到或者指定屬性的值）

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2）、當設置value為nil的時候，我們需要在類的實現里面重寫setNilValueForKey方法，不然會拋出NSInvalidArgumentException

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2、key路徑介紹

KVC除了操作對象的屬性之外，還可以操作對象的“復合屬性”，比如類里面的成員變量是對象，然后給這個成員變量的對象進行賦值，就這樣簡單理解，賦值之前一定要記得把這個對象進行初始化操作

KVC協議中為操作Key路徑的方法如下

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setValue:forKeyPath:根據Key設置屬性值

valueForKeyPath:根據key的路徑獲取屬性值

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2、測試簡單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 */

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User.m

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#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

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KVCPerson.h

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#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 */

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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

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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之前一定要記得把成員對象進行初始化，不然直接設置無效[person setValue:@"hello" forKeyPath:@"user.city"];NSLog(@"user.city is%@", [person valueForKeyPath:@"user.city"]);} }

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3、運行結果

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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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4、總結

在使用key的時候，一定要記得先把成員屬性的對象進行初始化，不然設置無效

如下

[person setValue:[User new] forKeyPath:@"user"];//在使用valueForKeyPath之前一定要記得把成員對象進行初始化，不然直接設置無效[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"]);

這樣結果會是null

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總結

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