SwiftUI XCode 13 TextField shouldChangeText property wiring - swiftui

Question

I'm using XCode 13 and SwiftUI (latest version)
I've got a simple TextField inside of a View.
TextField("enter barcode", value: $scannedBarcode, shouldChangeText : ?)
I cannot figure out how to use the shouldChangeText property of TextField.
I need an example of how to wire up this function.
I'm a newbie to SwiftUI, cannot find an example, and the developer docs are sorely lacking...
Apparently it looks like this maybe:
shouldChangeText(in: <UITextRange>, replacementText: <String>)
I'm very new to XCode (a few weeks) and need a solid example of how to use this to filter out all non whole numbers from a text field (no decimal point or alpha characters)
Thanks!
-----Edit----
With help below found this:
TextField("enter barcode", text: Binding(get: {scannedBarcode}, set: { scannedBarcode = String($0).replacingOccurrences( of:"[^0-9]", with: "", options: .regularExpression)}))
Which is great a filtering out non-digits going into the scannedBarcode variable. How can I prevent them from hitting the screen in the first place?

Answer 1

That is really simple in SwiftUI, you just have to use .onChange. Add this anywhere in your View:
.onChange(of: scannedBarcode) { newValue in
//do anything with newValue
}
It will give you the exact value of what's in the TextField.
For the UIKit one, it's the following function which is part of UITextFieldDelegate:
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool
}
UIKit with SwiftUI:
struct UTextField: UIViewRepresentable {
let placeHolder: String
#Binding var text: String?
init(_ placeHolder: String, text: Binding<String?>) {
self.placeHolder = placeHolder
self._text = text
}
func makeUIView(context: Context) -> UITextField {
let textField = UITextField()
textField.delegate = context.coordinator
textField.placeholder = placeHolder
return textField
}
func updateUIView(_ uiView: UITextField, context: Context) {
text = uiView.text
}
func makeCoordinator() -> Coordinator {
return Coordinator()
}
class Coordinator: NSObject, UITextFieldDelegate {
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
//do something
//whenever you don't want the text to be entered you return false
return true
}
}
}
Usage: UTextField("", text: $someText)