Delay in SwiftUI view appearing - swiftui

Question

I have a view that displays two calculated strings. At present, I calculate the strings with .onAppear. But the view does not render until the strings are calculated, leaving the user watching the previous view for 2 to 5 seconds till the calculation is done, and the progress bar never gets shown.
The code is:
struct CalculatingProgressView: View {
var body: some View {
ProgressView {
Text("Calculating")
.font(.title)
}
}
}
struct OffspringView: View {
#State private var males: String = ""
#State private var females: String = ""
#State private var busy = true
func determineOffspring() {
let temp = theOffspring(of: sire, and: dam)
males = temp.0
females = temp.1
busy = false
}
var body: some View {
Section(header: Text("Male Offspring")) {
Text(males)
.font(.callout)
}
if busy {
CalculatingProgressView()
}
Section(header: Text("Female Offspring")) {
Text(females)
.font(.callout)
}
.onAppear { determineOffspring() }
}
}
How can I get the view to render with a progress bar so the user knows that the app is actually doing something?

Answer 1

your code seems to work for me. You could try this approach,
to show the CalculatingProgressView while it's calculating determineOffspring.
var body: some View {
if busy {
CalculatingProgressView()
.onAppear { determineOffspring() }
} else {
Section(header: Text("Male Offspring")) {
Text(males).font(.callout)
}
Section(header: Text("Female Offspring")) {
Text(females).font(.callout)
}
}
}
}
Note, your theOffspring(...) in determineOffspring should use a completion closure something like
the following, to "wait" until the calculations are finished:
func determineOffspring() {
theOffspring(of: sire, and: dam) { result in
males = result.0
females = result.1
busy = false
}
}