SwiftUI validate input in textfields

Question

I am trying to validate user input in a TextField by removing certain characters using a regular expression. Unfortunately, I am running into problems with the didSet method of the text var calling itself recursively.

import SwiftUI
import Combine

class TextValidator: ObservableObject {

    @Published var text = "" {
        didSet {
            print("didSet")
            text = text.replacingOccurrences(
                of: "\\W", with: "", options: .regularExpression
            ) // `\W` is an escape sequence that matches non-word characters.
        }
    }

}


struct ContentView: View {

    @ObservedObject var textValidator = TextValidator()

    var body: some View {
        TextField("Type Here", text: $textValidator.text)
            .padding(.horizontal, 20.0)
            .textFieldStyle(RoundedBorderTextFieldStyle())

    }
}

On the swift docs (see the AudioChannel struct), Apple provides an example in which a property is re-assigned within its own didSet method and explicitly notes that this does not cause the didSet method to be called again. I did some testing in a playground and confirmed this behavior. However, things seem to work differently when I use an ObservableObject and a Published variable.

How do I prevent the didSet method from calling itself recursively?

I tried the examples in this post, but none of them worked. Apple may have changed things since then, so this post is NOT a duplicate of that one.

Also, setting the text back to oldValue within the didSet method upon encountering invalid characters would mean that if a user pastes text, then the entire text would be removed, as opposed to only the invalid characters being removed. So that option won't work.

Answer 1

Try to validate what you want in the TextField onRecive method like this:

class TextValidator: ObservableObject {

    @Published var text = ""

}

struct ContentView: View {

    @ObservedObject var textValidator = TextValidator()
    var body: some View {
        TextField("Type Here", text: $textValidator.text)
            .padding(.horizontal, 20.0)
            .textFieldStyle(RoundedBorderTextFieldStyle())
            .onReceive(Just(textValidator.text)) { newValue in
                let value = newValue.replacingOccurrences(
                    of: "\\W", with: "", options: .regularExpression)
                if value != newValue {
                    self.textValidator.text = value
                }
                print(newValue)
        }
    }
}