switching image on timed event in swift - swift

Question

I am trying to switch the displayed image in an UIImageView to different images based on an timed event by defining the what image should be displayed by I and the app works but when the timer gets to 5 the app crashes. if anyone can help me out then that would be great (also the Ad is the beginning of the image name so AD_1 - AD_4)
import UIKit
class ViewController: UIViewController {
//this is for declaring all the profile buttons
#IBOutlet weak var Icon_1: UIButton!
#IBOutlet weak var Icon_2: UIButton!
#IBOutlet weak var Icon_3: UIButton!
#IBOutlet weak var Icon_4: UIButton!
#IBOutlet weak var Icon_5: UIButton!
#IBOutlet weak var Icon_6: UIButton!
#IBOutlet weak var Icon_7: UIButton!
#IBOutlet weak var Icon_8: UIButton!
//this is used to swich the images
var i = Int(1)
let timer = Timer.scheduledTimer(timeInterval: 5.0, target: self, selector: #selector(fire), userInfo: nil, repeats: false)
//this is for the view
#IBOutlet weak var ad_view: UIView!
//this is for when the user swipes left
#IBAction func Icon_Swipe_Left(_ sender: Any) {
Icon_1.isHidden = true
Icon_2.isHidden = true
Icon_3.isHidden = true
Icon_4.isHidden = true
Icon_5.isHidden = false
Icon_6.isHidden = false
Icon_7.isHidden = false
Icon_8.isHidden = false
}
//this is when the user swipes right
#IBAction func Icon_Swipe_Right(_ sender: Any) {
Icon_1.isHidden = false
Icon_2.isHidden = false
Icon_3.isHidden = false
Icon_4.isHidden = false
Icon_5.isHidden = true
Icon_6.isHidden = true
Icon_7.isHidden = true
Icon_8.isHidden = true
}
// this is for decareing the image frame for the adds
#IBOutlet weak var Ad_Frame: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
//this is for showing the fist set of icons
Icon_1.isHidden = false
Icon_2.isHidden = false
Icon_3.isHidden = false
Icon_4.isHidden = false
//this is for hideing the second set of icons
Icon_5.isHidden = true
Icon_6.isHidden = true
Icon_7.isHidden = true
Icon_8.isHidden = true
self.Ad_Frame.image = UIImage(named: "AD_\(i)")
}
#objc func fire()
{
i += 1
self.Ad_Frame.image = UIImage(named: "AD_\(i)")
}
}

Answer 1

Two things:
1: you say you have images AD_1 - AD_4 - that's only four images, so it won't cope with the fifth! I'm assuming you mean AD_1 - AD_5
2: More importantly, you start with i = 1, and then add 1 before trying to display the image, so you're actually trying to display images 2...6.
Increment i after displaying the image, not before

Answer 2

Change fire so that it starts over once 5 is reached
#objc func fire() {
self.Ad_Frame.image = UIImage(named: "AD_\(i)")
i += 1
if i > 4 { i = 1 }
}
Off-topic but I would recommend renaming i to something more readable like counter for instance. Single letter variables are not recommended apart from in for loops. Also when declaring it you don't need to call Int(...) but assign the value directly instead, var counter = 1