Objective C 中的键值编码和键值观察是什么

Objective-C是一种面向对象的编程语言，它引入了键值编码（Key-Value Coding，简称KVC）和键值观察（Key-Value Observing，简称KVO）这两个重要的概念。这两个概念为开发者提供了便利的方法来访问和观察对象的属性和状态，使得代码编写更加简洁和灵活。

objective-c
@interface Person : NSObject
@property (nonatomic, strong) NSString *name;
@end
@implementation Person
@end

objective-c
Person *person = [[Person alloc] init];
[person setValue:@"John" forKey:@"name"];
NSLog(@"%@", [person valueForKey:@"name"]); // 输出：John

objective-c
@interface Person : NSObject
@property (nonatomic, strong) NSString *name;
@end
@implementation Person
@end

objective-c
Person *person = [[Person alloc] init];
[person addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
// 监听回调方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:@"name"]) {
        NSString *newName = change[NSKeyValueChangeNewKey];
        NSString *oldName = change[NSKeyValueChangeOldKey];
        NSLog(@"name属性发生变化，新值为：%@，旧值为：%@", newName, oldName);
    }
}