This kind of question was asked a zillion time. Delegates are not getting called because as of iOS 4 operations are started on a secondary thread. The thread probably exits before the delegates are called that’s all. Keep the connection on the main thread and handle the data in a background thread using GCD. I’v … Read more
GCD does not have built-in support for cancellation; if it’s important to be able to cancel your background task, then checking a flag like you’ve demonstrated is an acceptable solution. However, you may want to evaluate how quickly the cancellation needs to respond; if some of those methods calls are fairly short, you may be … Read more
Workaround: You can create NSOperation subclass (no generic), override main and call you own ‘execute’ func, which can be overriden by generic subclasses. Example: class SwiftOperation : NSOperation { final override func main() { execute() } func execute() { } } class MyOperation<T> : SwiftOperation { override func execute() { println(“My operation main was called”) … Read more
Doh. Dear future googlers: of course operation is nil when copied by the block, but it doesn’t have to be copied. It can be qualified with __block like so: //THIS MIGHT LEAK! See the update below. __block NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ while( ! [operation isCancelled]){ //do something… } }]; UPDATE: Upon further meditation, it … Read more
Okay, so as I understand it, you have two questions: Do you need the performSelectorOnMainThread: segment that appears in comments in your code? What does that code do? Why is the _isCancelled flag is not modified when you call cancelAllOperations on the NSOperationQueue that contains this operation? Let’s deal with these in order. I’m going … Read more
Cocoa Is My Girlfriend has a good tutorial on the use of NSOperation and NSOperationQueue. The tutorial makes use of NSOperation to download several webpages simultaneously in separate threads. Also, see this article from Mac Research.
My question is whether the database write operation occur in main thread or in a background thread? If you create an NSOperationQueue from scratch as in: NSOperationQueue *myQueue = [[NSOperationQueue alloc] init]; It will be in a background thread: Operation queues usually provide the threads used to run their operations. In OS X v10.6 and … Read more
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 … Read more
Your code won’t work because URLSessionDownloadTask runs asynchronously. Thus the BlockOperation completes before the download is done and therefore while the operations fire off sequentially, the download tasks will continue asynchronously and in parallel. While there are work-arounds one can contemplate (e.g., recursive patterns initiating one request after the prior one finishes, non-zero semaphore pattern … Read more
GCD is a low-level C-based API that enables very simple use of a task-based concurrency model. NSOperation and NSOperationQueue are Objective-C classes that do a similar thing. NSOperation was introduced first, but as of 10.5 and iOS 2, NSOperationQueue and friends are internally implemented using GCD. In general, you should use the highest level of … Read more