KVO 的代码简洁使用

1、类属性设置与创建

• 详细使用介绍
• KVO 键值观察

// KvoClass.h
@interface KvoClass : NSObject
@property(nonatomic, copy) NSString *name;
@end

// ViewController.m
@property(nonatomic, retain) KvoClass *kvoObject;
_kvoObject = [[KvoClass alloc] init];

2、KVO 添加

// 添加观察者
[_kvoObject addObserver:self
             forKeyPath:@"name"
                options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld
                context:@"nameChange"];
// 改变被观察的键对应的值
_kvoObject.name = @"xiao bai";
sleep(2);
_kvoObject.name = @"xiao hei";

3、KVO 回调

// 系统自带方法
- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
    if (context == @"nameChange") {
        NSLog(@"name 值被改变 kind = %@, oldValue = %@, newValue = %@",
                     change[@"kind"], change[@"old"], change[@"new"]);
    } 
    else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

4、KVO 移除

• 在实际工作中需要在合适的时候移除观察者身份。

- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath context:(nullable void *)context;
- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath;

- (void)dealloc {
    // 移除观察者
    [_kvoObject removeObserver:self forKeyPath:@"name" context:@"nameChange"];
}