Cancel a set of asynchronous operations with progress reports in iOS

Question

Suppose I use a different SDK (with which I have no control) with an API that imports 1 file asynchronously and causes completion to complete. The following is an example API.

func importFile(filePath: String, completion: () -> Void)

I need to import 10 files (one by one) using this API, but I need to cancel it, for example. after files 1,2,3 were successfully imported while file 4 is being imported, I want to be able to undo the whole set of operations (import of 10 files) so that file 4 is completed (since it is already running), but Files 5-10 will no longer be imported.

In addition, I also need to report on the progress of the import. When file 1 was successfully imported, I should report 10% progress (1 out of 10 completed).

How can i achieve this?

I am considering using NSOperationQueue with 10 NSOperations, but it seems like a progress report will be difficult.

Answer 1

So, I believe that from your question you follow as follows:

• Import n files in turn in a queue
• Report import progress of each file
• Ability to cancel the operation in the middle

This can be achieved using NSOperationQueueand NSBlockOperationas follows.

• Create classes AsyncBlockOperationand NSOperationQueue+AsyncBlockOperationfrom the code given in the answer to the following StackOverflow question: NSOperation wait while the asynchronous block is running
• Import both classes into a file that they will use

• Create an operation queue

  NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
  operationQueue.maxConcurrentOperationCount = 1;
  operationQueue.name = @"com.yourOrganization.yourProject.yourQueue";
  

• ,

  - (void)importFilesFromFilePathArray:(NSArray *)pathsArray
                      inOperationQueue:(NSOperationQueue *)operationQueue
                          withProgress:(void (^)(CGFloat progress))progressBlock {
  
    }
  

• , 2, NSBlockOperation NSOperationQueue

  for (int i = 0; i < pathsArray.count; i++) {
  
      [operationQueue addAsyncOperationWithBlock:^(dispatch_block_t completionHandler) {
          [self importFile:(NSString *)[pathsArray objectAtIndex:i] completion:^(bool completion) {
              [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                  CGFloat progress = (100 * (float)(i+1)/pathsArray.count);
                  progressBlock(progress);
                  if (progress == 100) {
                     successBlock(YES);
                  }
               }];
               completionHandler();
           }];
       }];
  }
  

• operationQueue,

  [operationQueue cancelAllOperations];
  

. . , :)

Answer 2

NSOperationQueue - .

• NSOperationQueue importQueue

:

• NSOperation
• , , , , , [ImportNumber: NSOperation]
• importQueue

---

:

1:

NSOperationQueue , operations, , , . (importQueue.operations.count).

2:

NSOperation . .

---

: Apple, asynchronous-nsoperation-why-and-how, , .

Answer 3

, . :

1Op = NSOperation..
2Op = NSOperation..
.
.
10Op = NSOperation..

10Op.addDependency(9Op)
9Op.addDependency(8Op) and so on...

cancel() {
    super.cancel()
    for dep in dependencies {
        dep.cancel()
    }
}