What is the best to write common code to call

I'm calling alerts, view's colours, spinners and components properties from Shared class. Is it ok. What is the best way to write common code.

Ex: My shared class code is...

import UIKit

class SharedClass: NSObject {

static let sharedInstance = SharedClass()

    var spinner = UIActivityIndicatorView()

//Show activity indicator
func activityIndicator() {

    DispatchQueue.main.async {
        if let window = UIApplication.shared.keyWindow {//Conditionally unwrap it instead of force unwrap

  //                let window = UIApplication.shared.keyWindow! //Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
            self.transparentView = UIView()
            self.transparentView?.frame = CGRect(x: 0, y: 0, width: window.frame.width, height: window.frame.height)
            self.transparentView?.backgroundColor = UIColor.black.withAlphaComponent(0.4)
            window.addSubview(self.transparentView!)

            if UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.pad {
                //                    self.spinner = UIActivityIndicatorView(style: .whiteLarge)
                self.spinner = UIActivityIndicatorView(style: .whiteLarge)
                self.spinner.frame = CGRect(x: 0, y: 0, width: 60, height: 60)
            } else {
                //                    self.spinner = UIActivityIndicatorView(style: .white)
                self.spinner = UIActivityIndicatorView(style: .white)
                self.spinner.frame = CGRect(x: 0, y: 0, width: 40, height: 40)
            }
            self.spinner.center = window.center
            self.transparentView?.addSubview(self.spinner)
            self.spinner.startAnimating()

            DispatchQueue.main.asyncAfter(deadline: .now() + 40.0) {//Stop spinner after 40 Sec's
                self.stopActivityIndicator()
            }
        }
    }
}

//Stop activity indicator
func stopActivityIndicator() {
    DispatchQueue.main.async {
        self.spinner.stopAnimating()
        self.spinner.removeFromSuperview()
        self.transparentView?.removeFromSuperview()//Some times getting error here
    }
}

 //Email validation
func isValidEmail(email: String) -> Bool {
    let emailRegex = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"
    var valid = NSPredicate(format: "SELF MATCHES %@", emailRegex).evaluate(with: email)
    if valid {
        valid = !email.contains("Invalid email id")
    }
    return valid
}

//Mobile number validation
func isValidPhone(phone: String) -> Bool {
    let phoneRegex = "^((0091)|(\\+91)|0?)[6789]{1}\\d{9}$"; // @"^((0091)|(\\+91)|0?)[6789]{1}\\d{9}$"        "^[0-9]{6,14}$"
    let valid = NSPredicate(format: "SELF MATCHES %@", phoneRegex).evaluate(with: phone)
    return valid
}

 private override init() {

}

}

//Alert function
extension UIViewController {
    func showAlert(title: String, msg: String) {
        DispatchQueue.main.async {
            let alert = UIAlertController(title: title, message: msg, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        }
    }
}

//Set TF shadow in login VC
extension UITextField {
    func TFProperties() {
        layer.shadowColor = UIColor(red: 199/255, green: 217/255, blue: 223/255, alpha: 1.0).cgColor
        layer.shadowOpacity = 1
        layer.shadowOffset = CGSize.zero
        layer.shadowRadius = 5
        layer.borderColor = UIColor(red: 199/255, green: 217/255, blue: 223/255, alpha: 1.0).cgColor
        layer.borderWidth = 1
        layer.cornerRadius = 4
    }
}

//Set View shadow in OTPVerify VC
extension UIView {
func subViewShadow() {
    layer.shadowColor = UIColor.white.cgColor
    layer.shadowOpacity = 1
    layer.shadowOffset = CGSize.zero
    layer.shadowRadius = 3
    layer.borderColor = UIColor.gray.cgColor
    layer.borderWidth = 1
    layer.cornerRadius = 4
}
func viewShadow() {
    layer.shadowColor = UIColor.gray.cgColor
    layer.shadowOpacity = 1
    layer.shadowOffset = CGSize.zero
    layer.shadowRadius = 3
}
func collectionViewCellBorder() {
    layer.cornerRadius = 5
    layer.borderColor = UIColor UIColor.gray.cgColor
    layer.borderWidth = 1.0
}
}