My issue: I have reason to believe that initializing a UIImage from Data gums up my main thread a bit. It isn't terrible, takes a fraction of a second to complete, but it is noticeable as it makes my UI seem a bit glitchy.
What I'm doing: I have a UIPageViewController. One of the UIViewControllers presented by said UIPageViewController is making use of this UIImage(data: Data) initializer in its viewDidLoad method:
class PageViewController: UIPageViewController {
var pages: [UIViewController] = []
override func viewDidLoad() {
super.viewDidLoad()
loadPages()
}
...
func loadPages() {
let vc1 = storyboard!.instantiateViewController(withIdentifier: "VC1") as! ViewController1
let vc2 = storyboard!.instantiateViewController(withIdentifier: "VC2") as! ViewController2
let vc3 = storyboard!.instantiateViewController(withIdentifier: "VC3") as! ViewController3
pages.append(userProfilePreviewVC)
pages.append(meetVC)
pages.append(chatLogVC)
setViewControllers([pages[1]], direction: UIPageViewController.NavigationDirection.forward, animated: false, completion: nil)
}
}
extension PageViewController: UIPageViewControllerDelegate, UIPageViewControllerDataSource {
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
switch currentIndex {
case 1:
return pages[0]
case 2:
return pages[1]
default:
return nil
}
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
switch currentIndex {
case 0:
return pages[1]
case 1:
return pages[2]
default:
return nil
}
}
}
Here is where the issue lies:
class ViewController1: UIViewController {
@IBOutlet var profilePicButton: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
let userPhotos = UserDefaults.standard.array(forKey: "UserPhotos") as? [Data] ?? []
if userPhotos.count != 0 {
self.profilePicButton.setImage(UIImage(data: userPhotos.first ?? Data()) ?? UIImage(named: "profile")!, for: .normal)
} else {
self.profilePicButton.setImage(UIImage(named: "profile"), for: .normal)
}
}
}
My question: When swiping on my PageViewController to the page that is displaying ViewController1, the main thread seems to gum up as it takes a fraction of a second to actually load this ViewController1. This is in contrast to other view controllers that are instantly ready to go when swiping to them. Similarly, when the user doesn't have any stored profile picture data, a placeholder image that is from my assets.xcassets folder takes its place. There is no lag when presenting this image. My question is: should I use UIImage(data: Data) on a background thread and update the button image when the UIImage has initialized?
