Cannot update value when wrapping SwiftUI binding in another binding - swiftui

Question

I want to make a login code screen. This consists of 4 separate UITextField elements, each accepting one character. What I did is implement a system whereby every time one of the UITextField's changes it will verify if all the values are filled out, and if they are update a boolean binding to tell the parent object that the code is correct.
In order to do this I wrap the #State variables inside a custom binding that does a callback on the setter, like this:
#State private var chars:[String] = ["","","",""]
...
var body: some View {
var bindings:[Binding<String>] = []
for x in 0..<self.chars.count {
let b = Binding<String>(get: {
return self.chars[x]
}, set: {
self.chars[x] = $0
self.validateCode()
})
bindings.append(b)
}
and those bindings are passed to the components. Every time my text value changes validateCode is called. This works perfectly.
However now I want to add an extra behavior: If the user types 4 characters and the code is wrong I want to move the first responder back to the first textfield and clear its contents. The first responder part works fine (I also manage that using #State variables, but I do not use a binding wrapper for those), however I can't change the text inside my code. I think it's because my components use that wrapped binding, and not the variable containing the text.
This is what my validateCode looks like:
func validateCode() {
let combinedCode = chars.reduce("") { (result, string) -> String in
return result + string
}
self.isValid = value == combinedCode
if !isValid && combinedCode.count == chars.count {
self.hasFocus = [true,false,false,false]
self.chars = ["","","",""]
}
}
hasFocus does its thing correctly and the cursor is being moved to the first UITextField. The text however remains in the text fields. I tried creating those bindings in the init so I could also use them in my validateCode function but that gives all kinds of compile errors because I am using self inside the getter and the setter.
Any idea how to solve this? Should I work with Observables? I'm just starting out with SwiftUI so it's possible I am missing some tools that I can use for this.
For completeness, here is the code of the entire file:
import SwiftUI
struct CWCodeView: View {
var value:String
#Binding var isValid:Bool
#State private var chars:[String] = ["","","",""]
#State private var hasFocus = [true,false,false,false]
#State private var nothingHasFocus:Bool = false
init(value:String,isValid:Binding<Bool>) {
self.value = value
self._isValid = isValid
}
func validateCode() {
let combinedCode = chars.reduce("") { (result, string) -> String in
return result + string
}
self.isValid = value == combinedCode
if !isValid && combinedCode.count == chars.count {
self.hasFocus = [true,false,false,false]
self.nothingHasFocus = false
self.chars = ["","","",""]
}
}
var body: some View {
var bindings:[Binding<String>] = []
for x in 0..<self.chars.count {
let b = Binding<String>(get: {
return self.chars[x]
}, set: {
self.chars[x] = $0
self.validateCode()
})
bindings.append(b)
}
return GeometryReader { geometry in
ScrollView (.vertical){
VStack{
HStack {
CWNumberField(letter: bindings[0],hasFocus: self.$hasFocus[0], previousHasFocus: self.$nothingHasFocus, nextHasFocus: self.$hasFocus[1])
CWNumberField(letter: bindings[1],hasFocus: self.$hasFocus[1], previousHasFocus: self.$hasFocus[0], nextHasFocus: self.$hasFocus[2])
CWNumberField(letter: bindings[2],hasFocus: self.$hasFocus[2], previousHasFocus: self.$hasFocus[1], nextHasFocus: self.$hasFocus[3])
CWNumberField(letter: bindings[3],hasFocus: self.$hasFocus[3], previousHasFocus: self.$hasFocus[2], nextHasFocus: self.$nothingHasFocus)
}
}
.frame(width: geometry.size.width)
.frame(height: geometry.size.height)
.modifier(AdaptsToSoftwareKeyboard())
}
}
}
}
struct CWCodeView_Previews: PreviewProvider {
static var previews: some View {
CWCodeView(value: "1000", isValid: .constant(false))
}
}
struct CWNumberField : View {
#Binding var letter:String
#Binding var hasFocus:Bool
#Binding var previousHasFocus:Bool
#Binding var nextHasFocus:Bool
var body: some View {
CWSingleCharacterTextField(character:$letter,hasFocus: $hasFocus, previousHasFocus: $previousHasFocus, nextHasFocus: $nextHasFocus)
.frame(width: 46,height:56)
.keyboardType(.numberPad)
.overlay(
RoundedRectangle(cornerRadius: 5)
.stroke(Color.init("codeBorder"), lineWidth: 1)
)
}
}
struct CWSingleCharacterTextField : UIViewRepresentable {
#Binding var character: String
#Binding var hasFocus:Bool
#Binding var previousHasFocus:Bool
#Binding var nextHasFocus:Bool
func makeUIView(context: Context) -> UITextField {
let textField = UITextField.init()
//textField.isSecureTextEntry = true
textField.keyboardType = .numberPad
textField.delegate = context.coordinator
textField.textAlignment = .center
textField.font = UIFont.systemFont(ofSize: 16)
textField.tintColor = .black
textField.text = character
return textField
}
func updateUIView(_ uiView: UITextField, context: Context) {
if hasFocus {
DispatchQueue.main.async {
uiView.becomeFirstResponder()
}
}
}
func makeCoordinator() -> Coordinator {
return Coordinator(self)
}
class Coordinator : NSObject, UITextFieldDelegate {
var parent:CWSingleCharacterTextField
init(_ parent:CWSingleCharacterTextField) {
self.parent = parent
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let result = (textField.text! as NSString).replacingCharacters(in: range, with: string)
if result.count > 0 {
DispatchQueue.main.async{
self.parent.hasFocus = false
self.parent.nextHasFocus = true
}
} else {
DispatchQueue.main.async{
self.parent.hasFocus = false
self.parent.previousHasFocus = true
}
}
if result.count <= 1 {
parent.character = string
return true
}
return false
}
}
}
Thanks!

Answer 1

you just make a little mistake, but i cannot believe you just "started" SwiftUI ;)
1.) just build textfield one time, so i took it as a member variable instead of building always a new one
2.) update the text in updateuiview -> that's it
3.) ...nearly: there is still a focus/update problem...the last of the four textfields won't update correctly ...i assume this is a focus problem....
try this:
struct CWSingleCharacterTextField : UIViewRepresentable {
#Binding var character: String
#Binding var hasFocus:Bool
#Binding var previousHasFocus:Bool
#Binding var nextHasFocus:Bool
let textField = UITextField.init()
func makeUIView(context: Context) -> UITextField {
//textField.isSecureTextEntry = true
textField.keyboardType = .numberPad
textField.delegate = context.coordinator
textField.textAlignment = .center
textField.font = UIFont.systemFont(ofSize: 16)
textField.tintColor = .black
textField.text = character
return textField
}
func updateUIView(_ uiView: UITextField, context: Context) {
uiView.text = character
if hasFocus {
DispatchQueue.main.async {
uiView.becomeFirstResponder()
}
}
}
func makeCoordinator() -> Coordinator {
return Coordinator(self)
}
class Coordinator : NSObject, UITextFieldDelegate {
var parent:CWSingleCharacterTextField
init(_ parent:CWSingleCharacterTextField) {
self.parent = parent
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let result = (textField.text! as NSString).replacingCharacters(in: range, with: string)
if result.count > 0 {
DispatchQueue.main.async{
self.parent.hasFocus = false
self.parent.nextHasFocus = true
}
} else {
DispatchQueue.main.async{
self.parent.hasFocus = false
self.parent.previousHasFocus = true
}
}
if result.count <= 1 {
parent.character = string
return true
}
return false
}
}
}