how to declare UIImageView in my UIViewController class so that other classes can use it?

Question

I will use GCD to run tasks that will in turn send tasks, that use wrist_band_UIImageView, to GCD main to  display.

IE.
1. ViewController starts backend task onto DispatchQueue.global which is an endless loop 
2. this endless loop periodically needs to update the UIImageView and so puts a task onto main queue to update the UIImageView.


class ViewController: UIViewController {  <<<<<<  E R R O R  Class 'ViewController' has no initializers

    @IBOutlet weak var app_title: UILabel!
    
    ////////////////////////   VARIABLES   ////////////////////////////

    var wrist_band_UIImageView: UIImageView


    override func viewDidLoad()              ///////////////////////////////////////// VIEW DID LOAD
    {
        print("viewDidLoad...")
        super.viewDidLoad()

        // Init data:
            let image = UIImage(systemName: "applewatch")      
            self.wrist_band_UIImageView = UIImageView(image: image!)

        print("viewDidLoad  starts run_app.")

        DispatchQueue.global().async{ app_class.run_app() }

        print("viewDidLoad done.")
        return   
    }
 }

UPDATE:
I changed UIImageView from static to instance, and now class line gets build error "Class 'ViewController' has no initializers".

Answer 1

I found this example that does the trick...........

Class ViewController: UIViewController {

    let someImageView: UIImageView = {
       let theImageView = UIImageView()
       theImageView.image = UIImage(named: "yourImage.png")
       theImageView.translatesAutoresizingMaskIntoConstraints = false //You need to call this property so the image is added to your view
       return theImageView
    }()

    override func viewDidLoad() {
       super.viewDidLoad()

       view.addSubview(someImageView) //This add it the view controller without constraints
       someImageViewConstraints() //This function is outside the viewDidLoad function that controls the constraints
    }

    // do not forget the `.isActive = true` after every constraint
    func someImageViewConstraints() {
        someImageView.widthAnchor.constraint(equalToConstant: 180).isActive = true
        someImageView.heightAnchor.constraint(equalToConstant: 180).isActive = true
        someImageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        someImageView.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 28).isActive = true
    }

}