How refresh UIVIewController to NSOperationQueue - iphone

Question

I have a view where I show an UIImageView which complimentary internet, I use to bring data NSXMLparser which are loaded correctly, the problem was that I use to make the parser NSOperationQueue background so then I refresh the image in my main view. image which form no refresh them in any way
I leave here the code below
- (void)viewDidLoad
{
[Base64 initialize];
[super viewDidLoad];
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self
selector:#selector(loadDataWithOperation)
object:nil];
[queue addOperation:operation];
[operation release];
}
- (void) loadDataWithOperation {
getData=NO;
NSURL *url1 = [ NSURL URLWithString:[url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
NSData *xmlData = [NSData dataWithContentsOfURL:url1];
NSXMLParser *parser = [[NSXMLParser alloc]initWithData:xmlData];
[parser setDelegate:self];
[parser parse];
[self performSelectorOnMainThread:#selector(showImage)withObject:nil waitUntilDone:NO];
}
-(void)showImage
{
NSArray *imagen =[[NSArray alloc] initWithArray:xml];
NSString *hola1 =[[imagen objectAtIndex:5]objectForKey:#"imagen"];
NSData * dataa = [Base64 decode:hola1];
img = [UIImage imageWithData:dataa];
self.images.image = img;
[images setImage:img];
[img release];
}
What am I doing wrong? appreciate your help please

Answer 1

I don't see anything obvious (though obviously we don't see the building of the xml array nor do we know precisely what the XML itself looks like). You should NSLog (or set a breakpoint and manually inspect) the xml as well as hola1 and dataa results in showImage, to identify at precisely what's going on at each step.
There are two possible problems with background operations and downloading XML. Neither of these seem applicable here, but I'll mention it just in case:
But there's nothing that would prevent the downloading and parsing of your XML like you have demonstrated here. If you were using NSURLConnection to download the XML (perhaps you simplified it here for the purposes of demonstration), there are issues in using NSURLConnection in a background queue. But if you use dataWithContentsOfURL (or better, NSXMLParser method initWithContentsOfURL) that wouldn't be an issue.
It looks like you're downloading a single XML, but if you were downloading multiple XML sources simultaneously, you should appreciate that many servers impose a limit as to how many concurrent connections they'll allow from a single client. You can use NSOperationQueue property maxConcurrentOperationCount to mitigate that problem. Four is a typical value.
Unrelated, but there are a couple of minor memory management things you might want to look at:
if you already have xml you don't need to create a new imagen;
you should probably release the queue object after adding the operation, or if you need to keep it around to reuse it, you should make it a class property or instance variable;
you could get rid of operation completely if you did:
[queue addOperationWithBlock:^{
[self loadDataWithOperation];
}];
you should release the parser object when you're done with it;
if you keep imagen in your code you should also release it when done; and
you should not release the img object since imageWithData returns an autorelease object
The routine memory management stuff probably would be pointed out to you if you did a static analysis (choose "Analyze" from the "Product" menu).
One final observation:
I notice that you have:
NSData *xmlData = [NSData dataWithContentsOfURL:url1];
NSXMLParser *parser = [[NSXMLParser alloc]initWithData:xmlData];
Clearly that xmlData is not necessary because you could have also just have done:
NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:url1];