Using NSOperationQueue in iOS to do Serial/Concurrent Operations.

By | May 7, 2016

NSOperationQueue is used to do scheduled operations in iOS. You can customize NSOperationQueue to do Concurrent/Serial operations.

You can set NSOperationQueue maxConcurrentOperationCount to tell it to do how many operations to execute at a time.

Lets see this with an example

[Swift Version]


import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {

let downloadQueue = NSOperationQueue();
downloadQueue.maxConcurrentOperationCount = 1;

for i in 1…10 {

let operation : NSBlockOperation = NSBlockOperation(block: {



func downloadImage (index : Int){

print("Download Started \(index)")
print("Download Complete \(index)")



In the above example, we set maxConcurrentOperationCount to 1, telling it to execute one by one.

[Objective C Version]


#import "ViewController.h"

@interface ViewController ()


@implementation ViewController

– (void)viewDidLoad {

[super viewDidLoad];

// Create a new NSOperationQueue instance.
operationQueue = [NSOperationQueue new];
operationQueue.maxConcurrentOperationCount = 1;

for(int i = 0; i < 10; i++){

NSNumber* iParam = [NSNumber numberWithInt:i];

// Create a new NSOperation object using the NSInvocationOperation subclass.
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self
// Add the operation to the queue and let it to be executed.
[operationQueue addOperation:operation];


-(void) downloadImage : (NSNumber *) index{

NSLog(@"Download Started %d", index.intValue);
NSLog(@"Download Complete %d", index.intValue);



With this you can schedule your operations so give a better user experience to the user.

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