is it correct to send UIImage between two controllers? - ios

Question

Is it appropriate to send UIImage between two Uiviewcontrollers?
I'm working on assignment 4 of CS193P Spring - Smashtag.
There I have to implement Mention Table View (It's kind of additional data of tweet: mentions, hashtags, images, urls). I have to place images to appropriate cell there. For that purpose I already download it. After that If user tap on one of that images It should segue to another UIViewController where user can zoom and scroll image.
In many examples which I've seen, people send url of image and fetch it again and again (for mention controller and the same image for another one). I think It decreases perfomance. So I send UIImage object between controllers.
But is it correct?
// MARK: - Navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == Storyboard.SearchSegue {
if let svc = segue.destinationViewController as? SearchResultsTableViewController {
if let cell = sender as? TextTableViewCell {
if let text = cell.hashtagLabel.text {
if text.hasPrefix("#") || text.hasPrefix("#") {
svc.searchText = text
}
}
}
} else if let svc = segue.destinationViewController as? ImageViewController {
if let cell = sender as? ImagesTableViewCell {
svc.image =
}
}
}
}
svc.image is var:
var image: UIImage? {
get {
return imageView.image
}
set {
imageView.image = newValue
imageView.sizeToFit()
scrollView?.contentSize = imageView.frame.size
}
}
and cell.imageVar
var imageVar: UIImage? {
get {
return imageField.image
}
set {
imageField.image = newValue
spinner.stopAnimating()
}
}
fetch function
private func fetchImage () {
if let u = url {
spinner?.startAnimating()
dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0)) {
let contentsOfURL = NSData(contentsOfURL: u)
dispatch_async(dispatch_get_main_queue()) {
if u == self.url {
if let imageData = contentsOfURL {
self.imageVar = UIImage(data: imageData)
} else {
self.spinner.stopAnimating()
}
}
}
}
}
}

Answer 1

That only make sense if you're using different image sizes. For instance, if you're using the image in a cell, you should use a small image, a thumbnail, to make the download faster. And then when you see the detail and want to zoom the image, you should use a bigger image (so you have to retrieve it using the url).
But if you only have one image size, it's totally correct to pass an UIImage through view controller.

Answer 2

You can think of caching the image. You can save the image in document directory and use its link to load in other places. One thing however you need to keep in mind is that you need to keep a track of how long you want the images to be cached this way, and a mechanism for deleting them. If you want the image only for one session you can even choose to use NSCache.