Setting subviews quicker than in viewDidLoad - ios

Question

Right now I'm allocating and initializing three UIImageViews that take up the entire screen and are stacked in the viewDidLoad method. Its actually taking some time to do this. Is there a way to do this automatically so the view just has them before its even loaded? like an init method that would speed this up?
- (void)viewDidLoad {
[super viewDidLoad];
self.mySubviews = [[NSMutableArray alloc] init];
self.videoCounterTags = [[NSMutableArray alloc] init];
int c = (int)[self.scenes count];
c--;
NSLog(#"int c = %d", c);
self.myCounter = [NSNumber numberWithInt:c];
for (int i=0; i<=c; i++) {
//create imageView
UIImageView *imageView =[[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
[imageView setUserInteractionEnabled:YES]; // <--- This is very important
imageView.tag = i; // <--- Add tag to track this subview in the view stack
[self.view addSubview:imageView];
NSLog(#"added image view %d", i);
//get scene object
PFObject *sceneObject = self.scenes[i];
//get the PFFile and filetype
PFFile *file = [sceneObject objectForKey:#"file"];
NSString *fileType = [sceneObject objectForKey:#"fileType"];
//check the filetype
if ([fileType isEqual: #"image"])
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//get image
NSURL *imageFileUrl = [[NSURL alloc] initWithString:file.url];
NSData *imageData = [NSData dataWithContentsOfURL:imageFileUrl];
dispatch_async(dispatch_get_main_queue(), ^{
imageView.image = [UIImage imageWithData:imageData];
});
});
}
//its a video
else
{
// the video player
NSURL *fileUrl = [NSURL URLWithString:file.url];
self.avPlayer = [AVPlayer playerWithURL:fileUrl];
self.avPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;
self.avPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:self.avPlayer];
//self.avPlayerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:[self.avPlayer currentItem]];
CGRect screenRect = [[UIScreen mainScreen] bounds];
self.avPlayerLayer.frame = CGRectMake(0, 0, screenRect.size.width, screenRect.size.height);
[imageView.layer addSublayer:self.avPlayerLayer];
NSNumber *tag = [NSNumber numberWithInt:i+1];
NSLog(#"tag = %#", tag);
[self.videoCounterTags addObject:tag];
}
}
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(viewTapped:)];
// dummyScreen is just a see through view that sits on top of my image stack and holds my tap gesture recognizer
[self.view bringSubviewToFront:self.dummyScreen];
[self.dummyScreen addGestureRecognizer:tapGesture];
}

Answer 1

The problem is this line:
dispatch_async(dispatch_get_global_queue...
That moves you onto a background thread, and thus there is no telling when the code will be executed. Hence the delay.
If these are local files (i.e., the URL is the file URL of an image file in your app bundle), there is no need for any dispatch_async in your code. Remove all of that and do everything on the main thread. That way, it will happen as fast as possible.
If these are remote files (i.e., you have to do networking to get hold of them), then there's probably nothing you can do to speed things up; networking takes time, and viewDidLoad is just about as early as you can possibly be notified that it's time to get hold of the images.