How to make ui responsive all the time and do background updating?

by

Grand Central Dispatch is easy to use for background loading. But GCD is only for after iOS4. If you have to support iOS3, performSelectorInBackground/performSelectorOnMainThread or NSOperationQueue are helpful.

And, be careful almost UIKit classes are not thread-safe except drawing to a graphics context. For example, UIScrollView is not thread-safe, UIImage imageNamed: is not thread-safe, but UIImage imageWithContentsOfFile: is thread-safe. 

dispatch_queue_t mainQueue = dispatch_get_main_queue();
dispatch_queue_t concurrentQueue =
    dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_async(concurrentQueue, ^{

    dispatch_apply([thumbnails count], concurrentQueue, ^(size_t index) {

        Thumbnail *thumbnail = [thumbnails objectAtIndex:index];
        thumbnail.image = [UIImage imageWithContentsOfFile:thumbnail.url];

        dispatch_sync(mainQueue, ^{

            /* update UIScrollView using thumbnail. It is safe because this block is on main thread. */

        });
    }

    /* dispatch_apply waits until all blocks are done */

    dispatch_async(mainQueue, ^{
        /* do for all done. */
    });
}

More Related Contents:

  1. HTML character decoding in Objective-C / Cocoa Touch
  2. Understanding reference counting with Cocoa and Objective-C
  3. When do you make an underscore in front of an instance variable? [duplicate]
  4. Why do you use an underscore for an instance variable, but not its corresponding property? [duplicate]
  5. `[super viewDidLoad]` convention
  6. What are best practices that you use when writing Objective-C and Cocoa? [closed]
  7. Property vs. instance variable
  8. How to write data in plist?
  9. Does UIGestureRecognizer work on a UIWebView?
  10. Open Source Cocoa/Cocoa-Touch POP3/SMTP library?
  11. Do you need to create an NSAutoreleasePool within a block in GCD?
  12. iPhone: Convert date string to a relative time stamp
  13. NSArray Equivalent of Map
  14. writing NSDictionary to plist in my app bundle
  15. Best way to implement Enums with Core Data
  16. How to write a simple Ping method in Cocoa/Objective-C
  17. Objective-C Category Causing unrecognized selector
  18. What’s the best way to put a c-struct in an NSArray?
  19. NSDateFormatter dateFromString returns nil
  20. Obtaining an NSDecimalNumber from a locale specific string?
  21. NSString to NSArray
  22. What’s the difference between “bundle display name” and “bundle name” in cocoa application’s info plist
  23. What is an easy way to break an NSArray with 4000+ objects in it into multiple arrays with 30 objects each?
  24. NSLocale currentLocale always returns “en_US” not user’s current language
  25. Using MD5 hash on a string in cocoa? [duplicate]
  26. How to set a custom font for entire iOS app without specifying size
  27. Multiple value enum in Obj-C
  28. Why tack a protocol of NSObject to a protocol implementation
  29. Convert hex data string to NSData in Objective C (cocoa)
  30. What’s the best way to use Obj-C 2.0 Properties with mutable objects, such as NSMutableArray?

Leave a Comment