On Sep 16, 2015, at 12:56 PM, Charles Srstka <cocoa...@charlessoft.com> wrote:
> - (void)setFoo:(MyObject *)foo {
> dispatch_async(dispatch_get_main_queue(), ^{
> [self willChangeValueForKey:@“foo”];
> });
>
> self.privateFoo = foo;
>
> dispatch_async(dispatch_get_main_queue(), ^{
> [self didChangeValueForKey:@“foo”];
> });
> }
This is not legitimate. The -willChangeValueForKey: must occur before the
property, as seen via its getter, has changed. This is necessary for observers
who ask for the old value, which can include KVO itself for key paths which go
through the property.
By dispatching it asynchronously, you allow the setting of privateFoo to
potentially happen before the -willChangeValueForKey: call.
Also, if multiple background threads set the foo property simultaneously, their
willChange… and didChange… calls can interleave, which is not kosher. So,
using dispatch_sync() wouldn't even solve the problem.
You would have to surround the whole body of the setter with a single dispatch
call (sync or async). And the getter would have to also dispatch synchronously
to the main queue so that it's properly coordinated and consistent with calls
to the setter. At that point, it's just better to move the setting of the
property like Jean did.
Regards,
Ken
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
