自定义KVO

1.自定义观察者方法

- (void)lz_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context {
    NSString *oldName = NSStringFromClass(self.class);
    NSString *newName = [NSString stringWithFormat:@"LZKVO_%@",oldName];
    //创建类
    Class customClass = objc_allocateClassPair(self.class, newName.UTF8String, 0);
    //注册类
    objc_registerClassPair(customClass);
    //修改指针
    object_setClass(self, customClass);
    //重写set方法
    NSString *methodName = [NSString stringWithFormat:@"set%@:",keyPath.capitalizedString];
    SEL sel = NSSelectorFromString(methodName);
    class_addMethod(customClass, sel, (IMP)customSetMethod, "v@:@");
    //保存观察者
    objc_setAssociatedObject(self, (__bridge const void*)@"observer", observer, OBJC_ASSOCIATION_ASSIGN);
}

2.重写set方法并通知观察者

void customSetMethod(id self, SEL _cmd, NSString *name) {
    //调用父类
    struct objc_super superClass = {
        self,
        class_getSuperclass([self class])
    };
    objc_msgSendSuper(&superClass, _cmd, name);
    id observer = objc_getAssociatedObject(self, (__bridge const void*)@"observer");
    //发出通知
    NSString *methodName = NSStringFromSelector(_cmd);
    NSRange range = NSMakeRange(3, setter.length - 4);
    NSString *key = [setter substringWithRange:range];
    NSString *letter = [[key substringToIndex:1] lowercaseString];
    key = [key stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:letter];
    objc_msgSend(observer, @selector(observeValueForKeyPath:ofObject:change:context:), key, self, @{key:name}, nil);
}