SwiftUI Combine How to update textfield - swiftui

Question

I'm learning Combine and how it can update a value using publishers. Currently I have created a variable that updates itself when validation fails.
var nameError: AnyPublisher<String, Never> {
$name
.dropFirst()
.debounce(for: 0.2, scheduler: RunLoop.main)
.removeDuplicates()
.map {
if $0.isEmpty || !self.isValidName() {
return "Name not valid"
}
return "Name"
}
.eraseToAnyPublisher()
}
I want to attach this to a Text() label so that it updates. Before Combine I would have an var error: String that I would check against. But now I get the error Cannot convert value of type 'AnyPublisher<String, Never>' to expected argument type 'String'
How do I convert a var error: String message to receive an AnyPublisher<String, Never>?

Answer 1

Below is a Playground that I think implements what you are asking.
The upshot is that you subscribe to your publisher in onAppear and keep the subscription in the state of your view. When a new value is published you update the state holding the caption.
import UIKit
import SwiftUI
import Combine
import PlaygroundSupport
class ModelObject : ObservableObject {
#Published var name: String = ""
var nameError: AnyPublisher<String, Never> {
$name
.dropFirst()
.debounce(for: 0.2, scheduler: RunLoop.main)
.print()
.removeDuplicates()
.map {
if $0.isEmpty || !self.isValidName() {
return "Name not valid"
}
return ""
}
.eraseToAnyPublisher()
}
func isValidName() -> Bool {
return name.caseInsensitiveCompare("Scott") != .orderedSame
}
}
struct TextControl : View {
#StateObject var viewModel = ModelObject()
#State var caption : String = ""
#State var subscription : AnyCancellable?
var body : some View {
VStack(alignment: .leading) {
TextField("Entry", text: $viewModel.name)
Text(caption)
.font(.caption)
.foregroundColor(.red)
}
.padding()
.frame(width: 320, height: 240)
.onAppear {
self.subscription = viewModel.nameError.sink { self.caption = $0}
}
}
}
let viewController = UIHostingController(rootView: TextControl())
PlaygroundSupport.PlaygroundPage.current.liveView = viewController