Hi John,
Since you're passing NSKeyValueObservingOptionInitial,
-observeValueForKeyPath: is going to be invoked on your object immediately,
before the method even returns.
Is your -observeValueForKeyPath: safe to be called with a partially set up
object?
Do you have any subclasses of your object? If so, -observeValueForKeyPath:
is getting called on them before they've done their work in init.
-Ken
On Mon, Sep 7, 2009 at 7:36 AM, John Chang <john.r.ch...@gmail.com> wrote:
> Hi all,
> Question: is it unsafe for some reason to be adding yourself as a KVO
> observer during -init?
>
> We have a singleton with an -init that looks something like this:
> - (id)init
> {
>
> if ((self = [super init]))
> {
>
> _foo = [[NSMutableDictionary alloc] init];
> _bar = [[NSMutableDictionary alloc] init];
>
> [[XYZManager sharedManager] addObserver:self forKeyPath:@"allObjects"
> options:NSKeyValueObservingOptionInitial context:NULL];
>
> }
> return self;
>
> }
> This code is running on iPhone OS. On some devices (we haven't been to
> narrow this down), the last line of code is throwing an exception:
>
> Sun Sep 6 13:41:26 unknown MyApp[1609] <Error>: *** Terminating app due to
> uncaught exception 'NSInvalidArgumentException', reason: '***
> -[NSCFDictionary setObject:forKey:]: attempt to insert nil key'
>
>
> We know that [XYZManager sharedManager] can't be nil, since otherwise
> -addObserver: would not be getting called, and the first line "if ((self =
> [super init]))" ensures that self can't be nil. We're pretty sure
> that [XYZManager sharedManager].allObjects is not nil, but even if it were
> nil, that shouldn't cause an exception. -allObjects is a synthesized getter
> with no dependent keys. No other threads are involved here.
>
> So we're stumped as to why KVO is throwing an exception. The only theory is
> that the NSKeyValueObservingOptionInitial option is causing KVO to do
> something with self immediately, but self isn't fully "set up" yet. Though
> it's unclear why in this particular usage that would be unsafe, or why it
> would make any difference. Can anyone provide any insight?
>
> Thanks,
> /John
> Stockholm, Sweden
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