SwiftUI - avoid AnyPublisher the first time - ios

Question

I've created publishers to validate the user input, in this case just validate they have 32 chars length.
ConnectionVM
import UIKit
import Combine
class ConnectionVM: ObservableObject {
private var cancellableSet: Set<AnyCancellable> = []
//INPUT
#Published var uuid1: String = ""
#Published var uuid2: String = ""
//OUTPUT
#Published var uuid1Message = ""
#Published var uuid2Message = ""
init() {
isUUID1ValidPublisher
.receive(on: RunLoop.main)
.map { valid in
valid ? "" : "UUID1 must have 32 characters"
}
.assign(to: \.uuid1Message, on: self)
.store(in: &cancellableSet)
isUUID2ValidPublisher
.receive(on: RunLoop.main)
.map { valid in
valid ? "" : "UUID2 must have 32 characters"
}
.assign(to: \.uuid2Message, on: self)
.store(in: &cancellableSet)
}
private var isUUID1ValidPublisher: AnyPublisher<Bool, Never> {
$uuid1
.debounce(for: 0.8, scheduler: RunLoop.main)
.removeDuplicates()
.map { input in
return input.count == 32
}
.eraseToAnyPublisher()
}
private var isUUID2ValidPublisher: AnyPublisher<Bool, Never> {
$uuid2
.debounce(for: 0.8, scheduler: RunLoop.main)
.removeDuplicates()
.map { input in
return input.count == 32
}
.eraseToAnyPublisher()
}
private var isFormValidPublisher: AnyPublisher<Bool, Never> {
Publishers.CombineLatest(isUUID1ValidPublisher, isUUID2ValidPublisher)
.map { uuid1IsValid, uuid2IsValid in
return uuid1IsValid && uuid2IsValid
}
.eraseToAnyPublisher()
}
}
ConnectionView
import SwiftUI
let lightGreyColor = Color(red: 239.0/255.0, green: 243.0/255.0, blue: 244.0/255.0, opacity: 1.0)
struct ConnectionView: View {
#ObservedObject var keyboardResponder = KeyboardResponder()
#ObservedObject var viewModel = ConnectionVM()
// #State var uuid1: String = ""
// #State var uuid2: String = ""
#State var authenticationDidFail: Bool = false
var body: some View {
return VStack {
WelcomeText()
LogoImage()
UUIDTextField(uuid: $viewModel.uuid1)
if !viewModel.uuid1Message.isEmpty {
Text(viewModel.uuid1Message)
.offset(y: -10)
.foregroundColor(.red)
}
UUIDTextField(uuid: $viewModel.uuid2)
if !viewModel.uuid2Message.isEmpty {
Text(viewModel.uuid2Message)
.offset(y: -10)
.foregroundColor(.red)
}
Button(action: {
print("Button tapped")
}) {
LoginButtonContent()
}
}
.padding()
.offset(y: -keyboardResponder.currentHeight*0.5)
}
struct WelcomeText : View {
var body: some View {
return Text("Welcome!")
.font(.largeTitle)
.fontWeight(.semibold)
.padding(.bottom, 20)
}
}
struct LogoImage : View {
var body: some View {
return Image("logo")
.resizable()
.aspectRatio(contentMode: .fill)
.frame(width: 150, height: 150)
.clipped()
.cornerRadius(150)
.padding(.bottom, 75)
}
}
struct UUIDTextField : View {
#Binding var uuid: String
var body: some View {
return TextField("UUID", text: $uuid)
.padding()
.background(lightGreyColor)
.cornerRadius(5.0)
.padding(.bottom, 20)
}
}
struct LoginButtonContent : View {
var body: some View {
return Text("LOGIN")
.font(.headline)
.foregroundColor(.white)
.padding()
.frame(width: 220, height: 60)
.background(Color.green)
.cornerRadius(15.0)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ConnectionView()
}
}
The problem is the first time when the screen is just opened, the error messages appear automatically.

Answer 1

You basically need another condition to guard whether to display the message.
That condition could be that the field has first changed, so you'd count the number of times each field has changed, and produce a Bool on whether it has changed more than once (i.e. beyond the initial assignment of "")
let hasUUID1Changed = $uuid1.scan(0, { a, _ in a + 1}).map { $0 > 1 }
let hasUUID2Changed = $uuid2.scan(0, { a, _ in a + 1}).map { $0 > 1 }
Publishers.Scan acts as the counter / accumulator in this case. The lifetime would be the lifetime of the view model.
Then you could use this publisher in combination with the isUUID1ValidPublisher to determine whether to display the message:
isUUID1ValidPublisher
.receive(on: RunLoop.main)
.combineLatest(hasUUID1Changed) // here
.map { (valid, changed) in
valid && !changed ? "" : "UUID1 must have 32 characters"
}
.sink { [weak self] self?.uuid1Message = $0 }
.store(in: &cancellableSet)