自定义KVO监听方式

kvo 观察者的本质是，是否有调用set方法

自定义KVO

实现观察People类的name属性

People.h

@interface People : NSObject

@property (nonatomic,copy)NSString *name;

@end

1.实现NSObject分类（类别）

.h文件中

#import

@interface NSObject (KVO)

- (void)ym_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;

@end

.m文件中

#import "NSObject+KVO.h"

#import

#import "NSKVONotifying_People.h"

NSString *const observerKey = @"observer";

@implementation NSObject (KVO)

-(void)ym_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context

{

    // 1.自定义NSKVONotifying_Person子类

    // 2.重写setName,在内部恢复父类做法，通知观察者

    // 3.如何让外界调用自定义Person类的子类方法，修改当前对象的isa指针，指向NSKVONotifying_Person

    objc_setAssociatedObject(self, (__bridge const void *)(observerKey), observer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

//修改isa指针

    object_setClass(self, [NSKVONotifying_People class]);

}

@end

2.创建NSKVONotifying_People 继承people类

.h文件中

#import "People.h"

@interface NSKVONotifying_People : People

@end

.m文件中

#import "NSKVONotifying_People.h"

#import

extern NSString *const observerKey;

@implementation NSKVONotifying_People

- (void)setName:(NSString *)name

{

    //恢复父类的set方法

    [super setName:name];

    // 通知观察者调用observeValueForKeyPath

    // 需要把观察者保存到当前对象

    // 获取观察者

  id observer = objc_getAssociatedObject(self, (__bridge const void *)(observerKey));

    [observer observeValueForKeyPath:@"name" ofObject:self change:nil context:nil];

}

@end

如何使用：

    People *p = [[People alloc] init];

    //调用自定义KVO

    [p ym_addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil];

实现下面方法

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

    NSLog(@"%@",_p.name);

}

到此结束