为什么NSOperation会禁用自动键值观察?

最可能的解释是kvo键与标准约定不匹配。通常有这样的方法 -isExecuting 和 -setExecuting: ,其中键路径为 @"executing" @"isExecuting" 相反。

-setIsExecuting: 改变这个值。相反,它们将executing/finished标志基于其他内部状态。在这种情况下,绝对需要使用显式的willChange/didChange通知。例如,如果我有一个NSOperation包装一个nsurl连接,我可能有2个ivar,其中一个名为 data 保存下载数据的 connection 它持有nsurl连接,我可以实现如下getter:

- (BOOL)isExecuting {
    return (connection != nil);
}

- (BOOL)isFinished {
    return (data != nil && connection == nil);
}

现在我的 -start

[self willChangeValueForKey:@"isExecuting"];
data = [[NSMutableData alloc] init]; // doesn't affect executing, but is used later
connection = [[NSURLConnection connectionWithRequest:request delegate:self] retain];
[self didChangeValueForKey:@"isExecuting"];

开始执行,以及

[self willChangeValueForKey:@"isExecuting"];
[self willChangeValueForKey:@"isFinished"];
[connection cancel];
[connection release];
connection = nil;
[self didChangeValueForKey:@"isFinished"];
[self didChangeValueForKey:@"isExecuting"];

结束。

automaticallyNotifiesObserversForKey 似乎有用,但我个人放弃了 isExecuting 和 isFinished executing finished

@property (nonatomic, readwrite, getter = isExecuting) BOOL executing;
@property (nonatomic, readwrite, getter = isFinished)  BOOL finished;

然后,我为这两个属性编写自定义设置器,它们执行必要的操作 I执行 和 完成了吗 通知:

- (void)setExecuting:(BOOL)executing
{
    [self willChangeValueForKey:@"isExecuting"];
    _executing = executing;
    [self didChangeValueForKey:@"isExecuting"];
}

- (void)setFinished:(BOOL)finished
{
    [self willChangeValueForKey:@"isFinished"];
    _finished = finished;
    [self didChangeValueForKey:@"isFinished"];
}

这将产生:

• 更习惯的 BOOL
• 自定义设置程序满足 NSOperation 需要;以及
• 我现在可以用 执行 和 完成

我必须承认我喜欢凌驾于 自动通知服务器市场

注意,如果在ios8或Yosemite中执行此操作,还必须在 @implementation :

@synthesize finished  = _finished;
@synthesize executing = _executing;

[self addObserver:self
       forKeyPath:@"isReady"
          options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial
          context:&ctxKVO_CSDownloadOperation];

[self addObserver:self
       forKeyPath:@"isExecuting"
          options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial
          context:&ctxKVO_CSDownloadOperation];

[self addObserver:self
       forKeyPath:@"isFinished"
          options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial
          context:&ctxKVO_CSDownloadOperation];

[self addObserver:self
       forKeyPath:@"isCancelled"
          options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial
          context:&ctxKVO_CSDownloadOperation];

...

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (context == &ctxKVO_CSDownloadOperation) {
        NSLog(@"KVO: %@", keyPath);
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

2017-08-02 14:29:58.831 CSDownloader[77366:5089399] isReady : 1
2017-08-02 14:29:58.831 CSDownloader[77366:5089399] KVO: isReady
2017-08-02 14:29:58.831 CSDownloader[77366:5089399] isExecuting : 0
2017-08-02 14:29:58.831 CSDownloader[77366:5089399] KVO: isExecuting
2017-08-02 14:29:58.831 CSDownloader[77366:5089399] isFinished : 0
2017-08-02 14:29:58.832 CSDownloader[77366:5089399] KVO: isFinished
2017-08-02 14:29:58.832 CSDownloader[77366:5089399] isCancelled : 0
2017-08-02 14:29:58.832 CSDownloader[77366:5089399] KVO: isCancelled
2017-08-02 14:29:58.832 CSDownloader[77366:5089399] isReady : 1
2017-08-02 14:29:58.832 CSDownloader[77366:5089399] KVO: isReady
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] isExecuting : 0
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] KVO: isExecuting
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] isFinished : 0
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] KVO: isFinished
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] isCancelled : 0
2017-08-02 14:29:58.833 CSDownloader[77366:5089399] KVO: isCancelled
2017-08-02 14:29:58.834 CSDownloader[77366:5089399] isReady : 1
2017-08-02 14:29:58.834 CSDownloader[77366:5089399] KVO: isReady
2017-08-02 14:29:58.834 CSDownloader[77366:5089399] isExecuting : 0

这个 NSOperationQueue 不是在观察 isFinished 或 isExecuting ,它正在观察 finished executing .

完成了吗 只是属性的合成get访问器 完成 . 将为此属性发送自动键值观察通知,除非您的子类通过实现 +automaticallyNotifiesObserversForKey +automaticallyNotifiesObserversOf<Key> 如果您没有选择退出自动KVO通知,则不需要使用执行手动通知 will/DidChangeValueForKey: 完成了吗 和 I执行 ,它们不是

TL;DR:这些不是NSOperationQueue要寻找的关键路径。

和 是正确的关键路径,它们应该发送自动KVO通知。

如果你是 关于KVO,并希望为get accessor键路径发送通知,例如 完成了吗 ,将属性注册为密钥路径的依赖项:

+ (NSSet *) keyPathsForValuesAffectingIsFinished {
    NSSet   *result = [NSSet setWithObject:@"finished"];
    return result;
}