Why my SwiftUI List is not getting updated? - binding

Question

I use a SwiftUI List and pass a String to a different view via a Binding.
But the list get not updated when I went back.
Here is my example:
struct ContentView: View {
#State private var list = ["a", "b", "c"]
#State private var item: String?
#State private var showSheet = false
var body: some View {
List {
ForEach(list.indices) { i in
Button(action: {
item = list[i]
showSheet.toggle()
}) {
Text(list[i])
}
}
}
.sheet(isPresented: $showSheet, content: {
DetailView(input: $item)
})
}
}
And the detail page:
struct DetailView: View {
#Binding var input: String?
var body: some View {
Text(input ?? "")
.onDisappear{
print("changed to changed")
input = "changed"
}
}
}
What I want to achieve is, that on every Item I click, I see the detail page. After that the element should change to "changed". But this does not happen. Why?

Answer 1

You update item but not list, so don't see any result. Here is corrected variant - store selected index and pass binding to list by index.
Tested with Xcode 12.1 / iOS 14.1
struct ContentView: View {
#State private var list = ["a", "b", "c"]
#State private var item: Int?
var body: some View {
List {
ForEach(list.indices) { i in
Button(action: {
item = i
}) {
Text(list[i])
}
}
}
.sheet(item: $item, content: { i in
DetailView(input: $list[i])
})
}
}
extension Int: Identifiable {
public var id: Self { self }
}
struct DetailView: View {
#Binding var input: String
var body: some View {
Text(input)
.onDisappear{
print("changed to changed")
input = "changed"
}
}
}

Answer 2

I recommend you use .sheet(item:content:) instead of .sheet(isPresented:content:)
struct ContentView: View {
#State private var items = ["a", "b", "c"]
#State private var selectedIndex: Int?
var body: some View {
List {
ForEach(items.indices) { index in
Button(action: {
selectedIndex = index
}) {
Text(items[index])
}
}
}
.sheet(item: $selectedIndex) { index in
DetailView(item: $items[index])
}
}
}
struct DetailView: View {
#Binding var item: String
var body: some View {
Text(item)
.onDisappear {
print("changed to changed")
item = "changed"
}
}
}
This will, however, require the selectedIndex to conform to Identifiable.
You can either create an Int extension:
extension Int: Identifiable {
public var id: Int { self }
}
or create a custom struct for your data (and conform to Identifiable).