How to cancel a thread running in the background ? (iOS)

Question

This is my function using dispatch queue , I would like to cancel it when it is running in the background. How can I do that?

 extension DispatchQueue {
    static func background(delay: Double = 0.0, background: (()->Void)? = nil, completion: (() -> Void)? = nil) {
        DispatchQueue.global(qos: .background).async {
            background?()
            if let completion = completion {
                DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: {
                    completion()
                })
            }
        }
    }       
 }

 DispatchQueue.background(background: {
        do {
        }
        catch let error {
            // Error handling
        }
    }, completion:{
 })

Answer 1

you can make use of DispatchWorkItem with DispatchGroup.

    // create a work item with the custom code
    let workItem = DispatchWorkItem {
          // Insert your code here
    }


   //Create dispatch group
    let dispatchGroup = DispatchGroup()

   // execute the workItem with dispatchGroup
    DispatchQueue.global().async(group: dispatchGroup, execute: workItem)

   //Handle code after the completion of global queue
    dispatchGroup.notify(queue: DispatchQueue.global()) {
            print("global queue execution completed")
        }

   //when the App goes to background cancel the workItem
     workItem.cancel()

Answer 2

You should definitely check the Apple Official Documentation concerning :

• OperationQueue

• BlockOperation

But also this WWDC 2014

Hope it will help you and build up your knowledge base about iOS and higher level API.