WanderingScouse WanderingScouse -4 years ago 112
Swift Question

Wait for all Operations in queue to finish before performing task

I have an Operation subclass and Operation queue with maxConcurrentOperationCount = 1.

This performs my operations in a sequential order that i add them which is good but now i need to wait until all operations have finished before running another process.

i was trying to use notification group but as this is run in a for loop as soon as the operations have been added to the queue the notification group fires.. How do i wait for all operations to leave the queue before running another process?

for (index, _) in self.packArray.enumerated() {

myGroup.enter()
let myArrayOperation = ArrayOperation(collection: self.outerCollectionView, id: self.packArray[index].id, count: index)
myArrayOperation.name = self.packArray[index].id
downloadQueue.addOperation(myArrayOperation)
myGroup.leave()

}

myGroup.notify(queue: .main) {
// do stuff here
}

Answer Source

You can use operation dependencies to initiate some operation upon the completion of a series of other operations:

let operationQueue = OperationQueue()

let completionOperation = BlockOperation {
    // do something
}

for object in objects {
    let operation = ...
    completionOperation.addDependency(operation)
    operationQueue.addOperation(operation)
}

OperationQueue.main.addOperation(completionOperation)
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