obj-c编程17:键值观察(KVO)(二)

2014-07-06 20:11:26.761 k[2109:507] My love girl is fanbinbin ... Does baba know?

爸爸监管的不错，可是儿子不高兴喽。hack儿子如何能让老爸如此侵犯隐私啊？咋办呢？不自动传递变更通知不就结了！为了实现手动通知，需要重写Son的类方法+automaticallyNotifiesObserversForKey，来告知obj-c你不想自动通知观察者自己的变化，注意是类方法哦！可以通过对特定的键名返回NO来完成：

+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
		if([key isEqualToString:@"girl_friend_name"])
			return NO;
		return YES;
	}

在Son类的实现中加入以上类方法，重新编译运行：

apple@kissAir: objc_src$./k

2014-07-06 20:37:36.726 k[2180:507] My love girl is lili ... Does baba know?

2014-07-06 20:37:36.729 k[2180:507] Yes , It's first time to induction son's girl_name!!!

2014-07-06 20:37:36.729 k[2180:507] My love girl is mimi ... Does baba know?

2014-07-06 20:37:36.730 k[2180:507] My love girl is libinbin ... Does baba know?

老爸”感应“不到喽！但是这样长了老爸会怀疑的啦，肿么宝贝儿子从不谈恋爱呢？这个不行哦！于是乎聪明的hack儿子可以再手动的通知老爸篡改后的内容啊！具体为：在Son属性写者方法的变化之前调用-willChangeva lueForKey,然后在变化之后调用-didChangeva lueForKey，重新改写写者方法吧，修改后完整代码如下：

#import 
  
   

#define msg(...) NSLog(__VA_ARGS__)
#define mki(x) [NSNumber numberWithInt:x]

@interface Son:NSObject{
	NSString *girl_friend_name;
}
	//在属性默认为atomic的情况下，如果自定义写者方法必须同时自定义读者方法，
	//或者将属性改为nonatomic模式。
	@property(nonatomic) NSString *girl_friend_name;
	-(void)think;
	-(void)fall_in_love_with:(NSString *)girl_name;
@end

@implementation Son
	@synthesize girl_friend_name;

	-(void)fall_in_love_with:(NSString *)girl_name{
		self.girl_friend_name = girl_name;
	}

	-(void)think{
		msg(@"My love girl is %@ ... Does baba know?",girl_friend_name);
	}

	+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
		if([key isEqualToString:@"girl_friend_name"])
			return NO;
		return YES;
	}

	-(void)setGirl_friend_name:(NSString *)name{
		[self willChangeva lueForKey:@"girl_friend_name"];
		//让老爸以为自己和女学霸谈恋爱哦
		girl_friend_name = @"女学霸";
		[self didChangeva lueForKey:@"girl_friend_name"];
		//恢复本色吧,BAD BOY... :)
		girl_friend_name = name;
	}
@end

@interface Baba:NSObject{
	Son *son;
}
	@property Son *son;
@end

@implementation Baba
	@synthesize son;

	-(id)initWithSon:(Son *)son_v{
		self = [super init];
		if(self){
			son = son_v;
			[son addObserver:self forKeyPath:@"girl_friend_name" \
				options:(NSKeyValueObservingOptionNew|\
				NSKeyValueObservingOptionOld|NSKeyValueObservingOptionInitial) \
				context:nil];
		}
		return self;
	}

	-(void)observeva lueForKeyPath:(NSString *)key_path \
		ofObject:(id)obj change:(NSDictionary *)change \
		context:(void *)context{

			NSString *old_name = [change objectForKey:NSKeyValueChangeOldKey];
			NSString *new_name = [change objectForKey:NSKeyValueChangeNewKey];

			if(!old_name){
				//NSKeyValueObservingOptionInitial选项的作用，第一次hook会发一次消息
				//以后每次更改会发一次消息。
				msg(@"Yes , It's first time to induction son's girl_name!!!");
			}else{
				if([new_name isEqualToString:@"libinbin"]){
					[obj fall_in_love_with:@"fanbinbin"];
				}
				msg(@"My son's %@ change from %@ to %@ ... That's OK? :(",\
				key_path,old_name,new_name);
			}
	}

	-(void)dealloc{
		[son removeObserver:self forKeyPath:@"girl_friend_name"];
		son = nil;
		//[super dealloc];
	}
@end

int main(int argc