Swift using function from delegated class as selector crashes - swift

Question

I have a custom view class, MyView, which inherits from UIView, and it contains a text field. I have added a delegate variable to this class which represents an instance of my ViewController class. This controller contains a function which I want to use as a selector in addTarget inside MyView:
class ViewController: UIViewController, UITextFieldDelegate {
let my_view = MyView()
override func viewDidLoad() {
super.viewDidLoad()
self.my_view.delegate = self
self.my_view.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(self.my_view)
// set up constraints
}
func handleDatePicker(sender: UIDatePicker) {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "MM/dd h:mm a"
self.my_view.time_text_field.text = "\(dateFormatter.string(from: sender.date))"
}
}
class MyView: UIView {
weak var delegate: ViewController! {
didSet {
self.time_text_field.delegate = self.delegate
}
}
lazy var time_text_field: UITextField = {
let text_field = UITextField()
let date_picker = UIDatePicker()
date_picker.addTarget(self, action: #selector(self.delegate.handleDatePicker(sender:)), for: .valueChanged)
text_field.inputView = date_picker
text_field.translatesAutoresizingMaskIntoConstraints = false
return text_field
}()
init() {
self.addSubview(self.time_text_field)
// set up constraints
}
}
When the function handleDatePicker gets called, the app crashes. However, when I move the function into the MyView class, the app no longer crashes:
class ViewController: UIViewController, UITextFieldDelegate {
let my_view = MyView()
override func viewDidLoad() {
super.viewDidLoad()
self.my_view.delegate = self
self.my_view.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(self.my_view)
// set up constraints
}
}
class MyView: UIView {
weak var delegate: ViewController! {
didSet {
self.time_text_field.delegate = self.delegate
}
}
lazy var time_text_field: UITextField = {
let text_field = UITextField()
let date_picker = UIDatePicker()
date_picker.addTarget(self, action: #selector(self.handleDatePicker(sender:)), for: .valueChanged)
text_field.inputView = date_picker
text_field.translatesAutoresizingMaskIntoConstraints = false
return text_field
}()
init() {
self.addSubview(self.time_text_field)
// set up constraints
}
func handleDatePicker(sender: UIDatePicker) {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "MM/dd h:mm a"
self.time_text_field.text = "\(dateFormatter.string(from: sender.date))"
}
}
Why does the app crash when the function used in #selector comes from the delegated class? Thanks.

Answer 1

The problem is that I was writing
date_picker.addTarget(self, action: #selector(self.delegate.handleDatePicker(sender:)), for: .valueChanged)
Instead of self for the first parameter, I should be using self.delegate:
date_picker.addTarget(self.delegate, action: #selector(self.delegate.handleDatePicker(sender:)), for: .valueChanged)