NSOperationQueue
has waitUntilAllOperationsAreFinished
, but I don't want to wait synchronously for it. I just want to hide progress indicator in UI when queue finishes.
What's the best way to accomplish this?
I can't send notifications from my NSOperation
s, because I don't know which one is going to be last, and [queue operations]
might not be empty yet (or worse - repopulated) when notification is received.
Use KVO to observe the operations
property of your queue, then you can tell if your queue has completed by checking for [queue.operations count] == 0
.
Somewhere in the file you're doing the KVO in, declare a context for KVO like this (more info):
static NSString *kQueueOperationsChanged = @"kQueueOperationsChanged";
When you setup your queue, do this:
[self.queue addObserver:self forKeyPath:@"operations" options:0 context:&kQueueOperationsChanged];
Then do this in your observeValueForKeyPath
:
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context
{
if (object == self.queue && [keyPath isEqualToString:@"operations"] && context == &kQueueOperationsChanged) {
if ([self.queue.operations count] == 0) {
// Do something here when your queue has completed
NSLog(@"queue has completed");
}
}
else {
[super observeValueForKeyPath:keyPath ofObject:object
change:change context:context];
}
}
(This is assuming that your NSOperationQueue
is in a property named queue
)
At some point before your object fully deallocs (or when it stops caring about the queue state), you'll need to unregister from KVO like this:
[self.queue removeObserver:self forKeyPath:@"operations" context:&kQueueOperationsChanged];
Addendum: iOS 4.0 has an NSOperationQueue.operationCount
property, which according to the docs is KVO compliant. This answer will still work in iOS 4.0 however, so it's still useful for backwards compatibility.