SwiftUI: How to execute closure when Alert is dismissed? - ios

Question

I've been trying out swiftUI and looked at this Ray Wenderlich tutorial... I noticed they didn't re-implement the "nextRound" functionality... so I tried to do it myself. Ran into a problem (which maybe they did, also):
The basic question is more general:
Using swiftUI, how do you trigger a function when an Alert is dismissed -- when the user clicks "OK." ?
I've tried using the dismissButton argument of the Alert constructor...
(and also the .onDisappear method of View but I can't figure out how to apply it to the Alert view.)
Code:
import SwiftUI
struct ContentView: View {
#State var shouldShowAlert: Bool = false
// this never gets called
func onAlertDismissed() {
print("you will not see this in the console")
}
// this doesn't seem to work
var dismissButton: some View {
Button(action: {
self.onAlertDismissed()
}) {
// Bilbo Baggins does not appear -- "OK" still shows
Text("BILBO BAGGINS")
}
}
var body: some View {
VStack {
Spacer()
Button(action: {
self.shouldShowAlert = true
}) {
Text("show the alert!")
}
Spacer()
}.alert(isPresented: $shouldShowAlert, content: {
// what to add here?
Alert(title: Text("Alert:"), message: Text("press OK to execute onAlertDismissed()..."))
// what I have tried and doesn't work:
/*
Alert(title: Text("Alert:"), message: Text("press OK to execute onAlertDismissed()..."), dismissButton: self.dismissButton as? Alert.Button)
*/
})
}
}

Answer 1

The button is constructed a little differently. You basically have to use a static factory method from Alert.Button to construct them and pass those in.
Alert(title: Text("Alert:"),
message: Text("press OK to execute default action..."),
dismissButton: Alert.Button.default(
Text("Press ok here"), action: { print("Hello world!") }
)
)
Alert(title: Text("Alert!"), message: Text("Message"),
primaryButton: Alert.Button.default(Text("Yes"), action: {
print("Yes")
}),
secondaryButton: Alert.Button.cancel(Text("No"), action: {
print("No")
})
)

Answer 2

It's possible to create alerts like this:
import SwiftUI
struct ContentView: View {
#State var showingAlert = false
var body: some View {
VStack {
HStack {
Button(action: {
self.showingAlert = true
})
{
Text("Save")
.font(.headline)
}
.alert(isPresented: $showingAlert, content: {
return Alert(
title: Text("Save Product"),
message: Text("Are you sure you want to save the changes made?"),
primaryButton: .default(Text("Yes"), action: {
//insert an action here
}),
secondaryButton: .destructive(Text("No")))
})
}
}
}
}

Answer 3

By looking at your code, it appears you don’t include a button in the alert propert, so your alert is not executing any action, in swiftui the alert signature is
init(title: Text, message: Text? = nil, primaryButton: Alert.Button, secondaryButton: Alert.Button)
Implement the signature properly is the first step