目录
基本使用
KVC的全称是Key-Value Coding,俗称键值编码，可以通过一个key来访问某个属性。
创建一个Person和Cat类
Person.h
NS_ASSUME_NONNULL_BEGIN
@interface Cat:NSObject
@property (nonatomic, assign) float weight;
@end
@interface Person : NSObject;
@property (nonatomic, strong) Cat * cat;
@property (nonatomic, assign) int age;
@end
NS_ASSUME_NONNULL_END
Person.m
#import "Person.h"
@implementation Cat
@end
@implementation Person
@end
使用案例
- (void)viewDidLoad {
[super viewDidLoad];
Person * person = [[Person alloc] init];
person.cat = [[Cat alloc] init];
[person addObserver:self
forKeyPath:@"age"
options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld
context:@"123"];
[person setValue:@18 forKey:@"age"];
[person setValue:@10 forKeyPath:@"cat.weight"];
NSLog(@"person.age=%@",[person valueForKey:@"age"]);
NSLog(@"person.cat.weight=%@",[person valueForKeyPath:@"cat.weight"]);
}
-(void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary<NSKeyValueChangeKey,id> *)change
context:(void *)context{
NSLog(@"object=%@",object);
NSLog(@"change=%@",change);
NSLog(@"context=%@",context);
}
打印日志为
iOSTest[540:67244] object=<Person: 0x2801bbd00>
iOSTest[540:67244] change={
kind = 1;
new = 18;
old = 0;
}
iOSTest[540:67244] context=123
iOSTest[540:67244] person.age=18
iOSTest[540:67244] person.cat.weight=10
分析
一、setValue:forKey:的原理
+(BOOL)accessInstanceVariablesDirectly；该方法的默认返回值是YES
二、valueForKey:的原理
行者常至，为者常成！