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 UIKitclass ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() let downloadQueue = NSOperationQueue(); downloadQueue.maxConcurrentOperationCount = 1; for i in 1...10 { let operation : NSBlockOperation = NSBlockOperation(block: { self.downloadImage(i) }) downloadQueue.addOperation(operation); } } func downloadImage (index : Int){ print("Download Started \(index)") sleep(2); 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 ()@end@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 selector:@selector(downloadImage:) object:iParam]; // 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); sleep(2); NSLog(@"Download Complete %d", index.intValue);}@end |
With this you can schedule your operations so give a better user experience to the user.
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