my app hangs when i start downloading using NsurlConnection - iphone

Question

I have an app that needs to download a sound file in order to work correctly.
I am using NSURLConnection asynchronously to download my file which is over 20Mb in size.
I placed a progressBarView in order to track the percentage of the downloading and I am using the delegate methods of NSUrlConnection as suggested by Apple.
NSURLRequest *theRequest=[NSURLRequest requestWithURL:soundFileURL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:20.0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection;
theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
//[theConnection cancel];
//[theConnection start];
if (theConnection) {
// Create the NSMutableData that will hold
// the received data
// receivedData is declared as a method instance elsewhere
receivedData=[[NSMutableData data] retain];
} else {
// inform the user that the download could not be made
}
and delegate methods
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
[receivedData appendData:data];
}
and So ...
When I start downloading, the interface hangs from time to time and the progressView hangs as well.
One notable thing, and maybe another question:
I disabled the user interface so the user has to wait until the download finishes and, of course, I give him a message to tell him that.
Would Apple reject my app for that? I am terribly worried about that
Thank you for reading my question :)

Answer 1

NSUrlConnection send events of NSURLConnectionDelegate to main thread by default. You should create new pool and runloop for this connection and be sure that it processed in background. Here are the example of downloading images in background. It using modified NSOperationQueue and NSOperation but you can easy modify it for downloading your file. LinkedImageFetcher on developer.apple.com

Answer 2

//1 First allocate NSOperationQueue object and set number of concurrent operations to execute at a time
NSOperationQueue *thumbnailQueue = [[NSOperationQueue alloc] init];
thumbnailQueue.maxConcurrentOperationCount = 3;
// load photo images in the background
__weak BHCollectionViewController *weakSelf = self;
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
UIImage *image = [photo image];
dispatch_async(dispatch_get_main_queue(), ^{
// then set them via the main queue if the cell is still visible.
cell.imageView.image = image;
}
});
}];
operation.queuePriority = (indexPath.item == 0) ?
NSOperationQueuePriorityHigh : NSOperationQueuePriorityNormal;
[thumbnailQueue addOperation:operation];
Create Photo class of NSObject and add below method
- (UIImage *)image
{
if (!_image && self.imageURL) {
NSData *imageData = [NSData dataWithContentsOfURL:self.imageURL];
UIImage *image = [UIImage imageWithData:imageData scale:[UIScreen mainScreen].scale];
_image = image;
}
return _image;
}