IOS Development --- asynchronous download and display of images

Download the image and asynchronously display the updated data to the foreground. There are many ways to do this. Two methods are mentioned in IOS as follows:

You need to define an imageview and a button as follows:

@property (retain, nonatomic) IBOutlet UIImageView *imageView;- (IBAction)download:(id)sender;
Method 1:
- (IBAction)download:(id)sender {    NSURL *url = [NSURL URLWithString:@"http://img6.cache.netease.com/cnews/2012/6/1/20120601085505e3aba.jpg"];        [NSThread detachNewThreadSelector:@selector(dowork:) toTarget:self withObject:url];    }
The dowork function is called.
-(void) dowork: (NSURL*) url{    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];    NSError *error;        NSURLRequest *request = [NSURLRequest requestWithURL:url];    NSHTTPURLResponse *response;        NSData* retData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];        if (response.statusCode == 200) {        UIImage* img = [UIImage imageWithData:retData];        [self   performSelectorOnMainThread:@selector(refreshUI:) withObject:img waitUntilDone:YES];            }    NSLog(@"d %d", response.statusCode);    [pool drain];    }
The UI update is notified after the download is completed in the dowork method. The function is as follows:
-(void) refreshUI:(UIImage* ) img{    self.imageView.image = img;}
Method 2 Use GCD to update the UI
-(Ibaction) download :( ID) sender {[self blockwork];} the button calls the block method to download and callback async to asynchronously update the UI to display the image-(void) blockwork {dispatch_queue_t queue; queue = dispatch_queue_create ("com. example. operation ", null); dispatch_async (queue, ^ {nsstring * urlstring = @" http://img6.cache.netease.com/cnews/2012/6/1/20120601085505e3aba.jpg "; nsdata * imagedata = [nsdata datawithcontentsofurl: [nsurl urlwithstring: urlstring]; uiimage * imge = [uiimage imagewithdata: imagedata]; dispatch_async (dispatch_get_main_queue (), ^ {self. imageview. image = imge ;});});
Use block document:
Http://www.devdiv.com/blocksprogramming key words: Chinese translation moderator -article-3205-1.html