Provide default value to properties in SwiftUI - swift

Question

I've learning SwiftUI for a week, recently I found a confusing issue with it.
#State private var checkAmount = 0.0
var body: some View {
NavigationView {
Form {
Section {
TextField("Amount", value: $checkAmount, format: .currency(code: Locale.current.currency?.identifier ?? "USD"))
.keyboardType(.decimalPad)
}
Section{
Text(checkAmount, format:.currency(code: Locale.current.currency?.identifier ?? "USD"))
}
}
}
}
I use TextFile to receive user's input and alter the value of checkAmount, and make the value shown in the section below. Here is my preview in xcode.
Preview
But when I type a random number and delete it all, this happend:
Still a digit here
It seems SwiftUI didn't delete it all, and still keep the last digit I deleted.
I guess maybe I should give it an default value when user's input is empty?
Some additional information maybe necessary: I'm using a M1 MacMini and XCode 14.1

Answer 1

Approach
For currency(code:) the value type is Decimal, so you have to use Optional Decimal
https://developer.apple.com/documentation/foundation/parseableformatstyle/3796617-currency
When the last digit is deleted it becomes nil
Use checkAmount ?? 0 in your TextField
Code
struct ContentView: View {
#State private var checkAmount = Decimal?(0.0) //Optional decimal
var body: some View {
NavigationView {
Form {
Section {
TextField("Amount", value: $checkAmount, format: .currency(code: Locale.current.currency?.identifier ?? "USD"))
.keyboardType(.decimalPad)
}
Section{
//Use ?? operator to display 0 when nil
Text(checkAmount ?? 0, format:.currency(code: Locale.current.currency?.identifier ?? "USD"))
}
}
.onChange(of: checkAmount) { newValue in
print("checkAmount = \(String(describing: newValue))")
}
}
}
}