Why does NSOperation disable automatic key-value observing?

Question

When working with a custom NSOperation subclass I noticed that the automatic key-value observing is disabled by the [NSOperation automaticallyNotifiesObse

Answer 1

While I agree that overriding automaticallyNotifiesObserversForKey appears to work, but I personally forgo the isExecuting and isFinished properties altogether and instead define executing and finished properties, which, as Kevin suggests, is more consistent with modern conventions:

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

I then write custom setters for these two properties, which do the necessary isExecuting and isFinished notifications:

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

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

This yields:

• a more customary BOOL property declaration;
• custom setters satisfy the strange notifications that NSOperation requires; and
• I can now just use the executing and finished setters throughout my operation implementation, without littering my code with notifications.

I must confess that I like the elegance of overriding automaticallyNotifiesObserversForKey, but I just worry about unintended consequences.

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Note, if doing this in iOS 8 or Yosemite, you will also have to explicitly synthesize these properties in your @implementation:

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