Loading overlay on collection view - ios

Question

I have a loading view that I insert over the top of a view while it is parsing data from the internet using a separate thread, in this case its on top of a UICollectionView.
For some reason that I cannot understand the loading overlay disappears on its own whist the parsing is still taking place, presenting a blank screen for a second or two. It doesn't seem to happen on UITableViews just on UIcollectionviews. Any help would be appreciated.
Activity overlay.m:
#import "ActivityOverlayController.h
#interface ActivityOverlayController ()
#end
#implementation ActivityOverlayController
-(id)initWithFrame:(CGRect)theFrame {
if (self = [super init]) {
frame = theFrame;
self.view.frame = theFrame;
}
return self;
}
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(#"%#", #"ActivityOverlayController called");
container = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 110, 30)];
activityLabel = [[UILabel alloc] init];
activityLabel.text = NSLocalizedString(#"Loading", #"string1");
activityLabel.textColor = [UIColor lightGrayColor];
activityLabel.font = [UIFont boldSystemFontOfSize:17];
[container addSubview:activityLabel];
activityLabel.frame = CGRectMake(0, 3, 70, 25);
activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
activityIndicator.color = [UIColor blackColor];
activityIndicator.hidesWhenStopped = TRUE;
[activityIndicator startAnimating];
activityIndicator.frame = CGRectMake(80, 0, 30, 30);
[container addSubview:activityIndicator];
[self.view addSubview:container];
container.center = CGPointMake(frame.size.width/2, frame.size.height/2);
self.view.backgroundColor = [UIColor colorWithRed:255 green:255 blue:255 alpha:0.7];
}
-(void)viewWillAppear:(BOOL) animated {
[super viewWillAppear:animated];
}
-(void)viewWillDisappear:(BOOL) animated {
[super viewWillDisappear:animated];
}
-(void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
[activityIndicator stopAnimating];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
#end
Parsing part of collectionViewController.m:
-(void)ParseCollectionView{
[self performSelectorOnMainThread:#selector(showActivityView) withObject:nil waitUntilDone:YES];
CollectionViewImages = [[NSMutableArray alloc]init];
NSData *xmlData = [[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:GalleryTitle]];
cvTBXML = [[TBXML alloc]initWithXMLData:xmlData];
// Obtain root element
TBXMLElement * root = cvTBXML.rootXMLElement;
TBXMLElement * channel = [TBXML childElementNamed:#"channel" parentElement:root];
if (root)
{
TBXMLElement * item = [TBXML childElementNamed:#"item" parentElement:channel];
while (item !=nil)
{
//create new instance of news object
NSObject *Imagetoparse = [[GalleryImage alloc] init];
TBXMLElement * link = [TBXML childElementNamed:#"link" parentElement:item];
NSString *linktext= [TBXML textForElement:link];
[Imagetoparse setValue:linktext forKey:#"link"];
TBXMLElement * thumbnail = [TBXML childElementNamed:#"description" parentElement:item];
NSString *Thumbnailtext= [TBXML textForElement:thumbnail];
Thumbnailtext = [Thumbnailtext substringFromIndex:21];
NSInteger *slength = Thumbnailtext.length -4;
Thumbnailtext = [Thumbnailtext substringToIndex:slength];
Thumbnailtext = [Thumbnailtext stringByReplacingOccurrencesOfString:#" " withString:#"%20"];
Thumbnailtext = [Thumbnailtext stringByReplacingOccurrencesOfString:#"thumb" withString:#"main"];
NSLog(#"Thumnail1 : %#", Thumbnailtext);
NSData *Thumbnailimage = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: Thumbnailtext]];
[Imagetoparse setValue:Thumbnailimage forKey:#"thumbnail"];
[CollectionViewImages addObject:Imagetoparse];
item = [TBXML nextSiblingNamed:#"item" searchFromElement:item];
}
}
[self.collectionView reloadData];
NSLog(#"%#", #"Finished Parse Collection View");
[self performSelectorOnMainThread:#selector(hideActivityView) withObject:nil waitUntilDone:NO];
}
-(void)showActivityView {
if (overlayController == nil) {
overlayController = [[ActivityOverlayController alloc] initWithFrame:(self.view.superview.bounds)];
}
[self.view.superview insertSubview:overlayController.view aboveSubview:self.view];
}
-(void)hideActivityView {
[overlayController.view removeFromSuperview];
}