Swift UI - Button back on image gallery - ios

Question

How do I make a back button? I get it wrong the way I want to do it. Thank you in advance.
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var imageView: UIImageView!
let images: [UIImage] = [#imageLiteral(resourceName: "tub"),#imageLiteral(resourceName: "ball"),#imageLiteral(resourceName: "apple"),#imageLiteral(resourceName: "igloo"),#imageLiteral(resourceName: "frog")]
var i : Int = 0
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
#IBAction func nextButton(_ sender: UIButton) {
i = (i+1)%images.count
imageView.image = images[i]
}
#IBAction func backButton(_ sender: UIButton) {
i = (i-1)%images.count
imageView.image = images[i]
}
the back button gives an error

Answer 1

You have 5 images in your array.
When you tap your Back button, suppose i is currently equal to 0:
(i-1) == -1
-1 % 5 == -1
imageView.image = images[-1] // is invalid... there is no array index of -1
If you want the Back button to "wrap around" from 0 (the first image) to 4 (the last image), you should do:
i -= 1
if i < 0 {
i = images.count - 1
}
imageView.image = images[i]
If you want to stop at the first image:
i = max(i - 1, 0)
imageView.image = images[i]