Class to protocol conversation in swift - swift

Question

I have this heavy basicVC Class subclass of UIViewController that I am trying to convert as vcprotocol.
It's the basicVC that is doing all work like god class. Which I would like to break into as vcProtocol.
I am trying to do is a separation of concern. Not all of the ViewControllers need to show the Alert View or Network not connected msg.
For example, I have indicatorView that I create in protocol extension as computed property. No error warning but no indicator is being shown. When I try to debug and do po acticvityIndicator I get the following error, which indicates that activityIndicator was never allocated.
error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=1, address=0x5a1012de027).
The process has been returned to the state before expression evaluation.
Code snippet:
protocol vcProtocol {
var activityIndicator: UIActivityIndicatorView { get }
}
protocol extension:
extension vcProtocol where Self: UIViewController {
var activityIndicator: UIActivityIndicatorView {
let indicator = UIActivityIndicatorView(style: UIActivityIndicatorView.Style.gray)
indicator.hidesWhenStopped = true
indicator.style = .whiteLarge
indicator.color = .red
indicator.backgroundColor = UIColor.gray
indicator.translatesAutoresizingMaskIntoConstraints = false
return indicator
}
func showLoadingIndicator() {
activityIndicator.startAnimating()
activityIndicator.isHidden = false
}
func hideLoadingIndicator() {
activityIndicator.stopAnimating()
activityIndicator.isHidden = true
}
}
I am not able to wrap my head around how to solve this. as I can only have computed properties in the protocol.
so I have them as get only properties.
my plan is to use the protocol extension to provide a default implementation.
Any thoughts on how to solve this problem.

Answer 1

This activityIndicator is a computed property, so every time you reference the computed property, that get block will be called. The net effect is that, as written, each time you reference activityIndicator, you’re going to get a new instance of UIActivityIndicatorView, which is obviously not your intent.
Consider your showLoadingIndicator:
func showLoadingIndicator() {
activityIndicator.startAnimating()
activityIndicator.isHidden = false
}
The first line (with startAnimating) will return a new UIActivityIndicatorView and the second line (with isHidden) will return yet another. And neither of these will be the same one that you presumably added to your subview.
This activityIndicator really should be instantiated once and only once. Unfortunately, you can’t define the stored property in an extension, so there are a few approaches:
You can let the UIViewController declare the stored property and just define methods method to configure, show, and hide it:
protocol LoadingIndicatorProtocol: class {
var loadingActivityIndicator: UIActivityIndicatorView? { get set }
}
extension LoadingIndicatorProtocol where Self: UIViewController {
func addLoadingIndicator() {
let indicator = UIActivityIndicatorView(style: .gray)
indicator.hidesWhenStopped = true
indicator.style = .whiteLarge
indicator.color = .red
indicator.backgroundColor = .gray
indicator.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(indicator)
// you might want to add the constraints here, too
loadingActivityIndicator = indicator
}
func showLoadingIndicator() {
loadingActivityIndicator?.startAnimating()
loadingActivityIndicator?.isHidden = false
}
func hideLoadingIndicator() {
loadingActivityIndicator?.stopAnimating()
loadingActivityIndicator?.isHidden = true
}
}
And then a UIViewController subclass simply has to define its own ivar for the activityIndicator, e.g.
class ViewController: UIViewController, LoadingIndicatorProtocol {
var loadingActivityIndicator: UIActivityIndicatorView?
override viewDidLoad() {
super.viewDidLoad()
addLoadingIndicator()
}
...
}
The other approach is to use associated objects via objc_getAssociatedObject and objc_setAssociatedObject, to achieve stored property behavior:
protocol LoadingIndicatorProtocol {
var loadingActivityIndicator: UIActivityIndicatorView { get }
}
private var associatedObjectKey = 0
extension LoadingIndicatorProtocol {
var loadingActivityIndicator: UIActivityIndicatorView {
if let indicatorView = objc_getAssociatedObject(self, &associatedObjectKey) as? UIActivityIndicatorView {
return indicatorView
}
let indicator = UIActivityIndicatorView(style: .gray)
indicator.hidesWhenStopped = true
indicator.style = .whiteLarge
indicator.color = .red
indicator.backgroundColor = .gray
indicator.translatesAutoresizingMaskIntoConstraints = false
objc_setAssociatedObject(self, &associatedObjectKey, indicator, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
return indicator
}
func showLoadingIndicator() {
loadingActivityIndicator.startAnimating()
loadingActivityIndicator.isHidden = false
}
func hideLoadingIndicator() {
loadingActivityIndicator.stopAnimating()
loadingActivityIndicator.isHidden = true
}
}