SwiftUI: Displaying slider position in a seperate label - swiftui

Question

This question is a bit of a follow on from SwiftUI: How to get continuous updates from Slider
Basically I have a slider which is one of a number of sliders. Each on changes a parameter on a model class so I'm passing in a binding which represents a specific property on the model class. This works in that the model gets the new value each time the slider moves.
struct AspectSlider: View {
private var value: Binding<Double>
init(value: Binding<Double>, hintKey: String) {
self.value = value
}
var body: some View {
VStack(alignment: .trailing) {
Text("\(self.value.value)")
Slider(value: Binding<Double>(getValue: { self.value.value }, setValue: { self.value.value = $0 }),
from: 0.0, through: 4.0, by: 0.5)
}
}
}
What isn't working correctly is the Text("\(self.value.value)") display which is meant to show the current value of the slider. It's not updating when the Binding<Double> value changes.
Instead it only updates when something else on the display triggers a display refresh. In my case the label that represents the result of the calculating performed by the model (which doesn't necessarily change when a slider changes it's value).
I've confirmed that the model is getting changes so the binding is updating. My question is why is the Text label not updating immediately.

Answer 1

Ok, I've worked out why my code wasn't updating as it should. It came down to my model which looks like this (Simple version):
final class Calculator: BindableObject {
let didChange = PassthroughSubject<Int, Never>()
var total: Int = 0
var clarity: Double = 0.0 { didSet { calculate() }}
private func calculate() {
if newValue.rounded() != Double(total) {
total = Int(newValue)
didChange.send(self.total)
}
}
}
What was happening was that the value on the sider was only updating when this model executed the didChange.send(self.total) line. I think, if I've got this right, that because the label is watching a binding, only when the binding updates does the label update. Makes sense. Still working this out.
I guess it part of learning about Combine and how it works :-)

Answer 2

Your code, if called like this, works fine:
struct ContentView: View {
#State private var value: Double = 0
var body: some View {
AspectSlider(value: $value, hintKey: "hint")
}
}
struct AspectSlider: View {
private var value: Binding<Double>
init(value: Binding<Double>, hintKey: String) {
self.value = value
}
var body: some View {
VStack(alignment: .trailing) {
Text("\(self.value.value)")
Slider(value: Binding<Double>(getValue: { self.value.value }, setValue: { self.value.value = $0 }),
from: 0.0, through: 4.0, by: 0.5)
}
}
}
Note that you can also take advantage of the property wrapper #Binding, to avoid using self.value.value. Your implementation should change slightly:
struct AspectSlider: View {
#Binding private var value: Double
init(value: Binding<Double>, hintKey: String) {
self.$value = value
}
var body: some View {
VStack(alignment: .trailing) {
Text("\(self.value)")
Slider(value: Binding<Double>(getValue: { self.value }, setValue: { self.value = $0 }),
from: 0.0, through: 4.0, by: 0.5)
}
}
}