CODEWITHSUNDEEP
iosswiftmultithreading
user172902
user172902

Reputation: 3581

Do I need dispatch_get_main_queue in completion block

In one of the tutorial from Ray Wenderlich Series, he used dispatch_get_main_queue() inside the completion block as follows

func startFiltrationForRecord(photoDetails: PhotoRecord, indexPath: NSIndexPath){
  if let filterOperation = pendingOperations.filtrationsInProgress[indexPath]{
    return
  }

  let filterer = ImageFiltration(photoRecord: photoDetails)
  filterer.completionBlock = {
    if filterer.cancelled {
      return
    }
    dispatch_async(dispatch_get_main_queue(), {
      self.pendingOperations.filtrationsInProgress.removeValueForKey(indexPath)
      self.tableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
      })
  }
  pendingOperations.filtrationsInProgress[indexPath] = filterer
  pendingOperations.filtrationQueue.addOperation(filterer)
}

Even though he briefly explained why the completion block is required, I was wondering if anyone could answer the following questions

In my own app, I have completion block in quite a lot of place (with reloading table view code in completion block like his. However, I don't not have a single dispatch_get_main_queue code. Does that mean for all UI related task in completion block, I NEED to add dispatch_get_main_queue?

Upvotes: 1

Views: 430

Answers (1)

technerd
technerd

Reputation: 14504

Yes , you have to use main queue to update tableview. As any UI update should be perform on main thread.

So you must have to reload table on main thread.

dispatch_async(dispatch_get_main_queue(), ^{

            // Perform UI operations here
        });

It is advisable to perform all calculations, network related functions on secondary thread or background thread, when it comes to perform operation related to UIKit, then simple switch back to main thread using above mention code.

Upvotes: 2

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