Activating animation only after all images loaded from urls array - ios

Question

I started studying ObjectiveC not too long ago and I'm trying to write an app that has two UIImageViews and an array of URLs to load from web. After loading all the images from the URLs asynchronously, I would like to start animation on the UIImageViews that change pictures every 3 seconds. My only issue is that I don't want the animations until after all the images have been downloaded. the code I've got far is:
- (void)viewWillAppear:(BOOL)animated
{
self.imagesArray = [[NSMutableArray alloc] init];
[self initUrlArrayAndGetImages];
}
- (void)initUrlArrayAndGetImages
{
self.urlsArray = #[#"abc.com/1.png",
#"abc.com/2.png",
#"abc.com/3.png"];
for (int i = 0; i < [self.urlsArray count]; i++)
{
NSString *string = [self.urlsArray objectAtIndex:i];
NSURL *urlFromString = [NSURL URLWithString:string];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:urlFromString];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:[NSOperationQueue currentQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError)
{
if (!connectionError)
{
UIImage *imageFromData = [UIImage imageWithData:data];
[self.imagesArray addObject:imageFromData];
}
else
{
NSLog(#"%#, %#", connectionError, [connectionError userInfo]);
}
}];
}
So where will I call the method that activates the animation from? Because if I call it at the completion of the block it adds an image at a time (very fast, true, but still refreshes the method all the time...). What is my best solution?
Thanks in advance

Answer 1

You could add an if() statement checking to see if the count of images in the imagesArray is equal to the count of URLs in the urlsArray. If so, then call the animation. This would look like:
if (!connectionError)
{
UIImage *imageFromData = [UIImage imageWithData:data];
[self.imagesArray addObject:imageFromData];
if(self.imagesArray.count == self.urlsArray.count)
{
// All images are loaded successfully
// Activate animation
}
}
else
{
NSLog(#"%#, %#", connectionError, [connectionError userInfo]);
}
It's important to note that this will only work if all images were downloaded successfully. If one or more result in a connection error, it will not call the animation. To get around this, you could easily implement a dedicated count variable that is incremented when the completionHandler is called, whether or not there was a connection error. Then use this to compare to self.urlsArray.count.

Answer 2

In your completion handler you're adding the downloaded images to your self.imagesArray. Add code that compares imagesArray.count to urlsArray.count. If they are equal, all downloads have been completed and you can begin your animation:
[NSURLConnection sendAsynchronousRequest:urlRequest queue:[NSOperationQueue currentQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError)
{
if (!connectionError)
{
UIImage *imageFromData = [UIImage imageWithData:data];
[self.imagesArray addObject:imageFromData];
if (self.imagesArray.count == self.urlsArray.count)
{
//All downloads are complete. Trigger the animation
}
else
{
NSLog(#"%#, %#", connectionError, [connectionError userInfo]);
}
}];