Simple SwiftUI CRUD using structs rather than classes? - swift

Question

I have a complex data structure which uses value types (structs and enums), and I'm facing major issues getting basic CRUD to work. Specifically:
How best to "Re-bind" a value in a ForEach for editing by a child view
How to remove/delete a value
Rebinding
If I have an array of items as #State or #Binding, why isn't there a simple way to bind each element to a view? For example:
import SwiftUI
struct Item: Identifiable {
var id = UUID()
var name: String
}
struct ContentView: View {
#State var items: [Item]
var body: some View {
VStack {
ForEach(items, id: \.id) { item in
TextField("name", text: $item) // 🛑 Cannot find '$item' in scope
}
}
}
}
Workaround
I've been able to work around this by introducing a helper function to find the correct index for the item within a loop:
struct ContentView: View {
#State var items: [Item]
func index(of item: Item) -> Int {
items.firstIndex { $0.id == item.id } ?? -1
}
var body: some View {
VStack {
ForEach(items, id: \.id) { item in
TextField("name", text: $items[index(of: item)].name)
}
}
}
}
However, that feels clunky and possibly dangerous.
Deletion
A far bigger issue: how are you supposed to correctly delete an element? This sounds like such a basic question, but consider the following:
struct ContentView: View {
#State var items: [Item]
func index(of item: Item) -> Int {
items.firstIndex { $0.id == item.id } ?? -1
}
var body: some View {
VStack {
ForEach(items, id: \.id) { item in
TextField("name", text: $items[index(of: item)].name)
Button( action: {
items.remove(at: index(of: item))
}) {
Text("Delete")
}
}
}
}
}
Clicking the "Delete" button on the first few items works as expected, but trying to Delete the last item results in Fatal error: Index out of range...
My particular use case doesn't map to a List, so I can't use the deletion helper there.
Reference types
I know that reference types make much of this easier, especially if they can conform to #ObservableObject. However, I have a massive, nested, pre-existing value type which is not easily converted to classes.
Any help would be most appreciated!
Update: Suggested solutions
Deleting List Elements from SwiftUI's list: The accepted answer proposes a complex custom binding wrapper. Swift is powerful, so it's possible to solve many problems with elaborate workarounds, but I don't feel like an elaborate workaround should be necessary to have a list of editable items.
Mark Views as "deleted" using State or a private variable, then conditionally hide them, to avoid out-of-bounds errors. This can work, but feels like a hack, and something that should be handled by the framework.

Answer 1

I confirm that more appropriate approach for CRUD is to use ObservableObject class based view model. And an answer provided by #NewDev in comments is a good demo for that approach.
However if you already have a massive, nested, pre-existing value type which is not easily converted to classes., it can be solved by #State/#Binding, but you should think about what/when/and how update each view and in each order - that is the origin of all such index out of bounds on delete issues (and some more).
Here is demo of approach of how to break this update dependency to avoid crash and still use value types.
Tested based on your code with Xcode 11.4 / iOS 13.4 (SwiftUI 1.0+)
struct ContentView: View {
#State var items: [Item] = [Item(name: "Name1"), Item(name: "Name2"), Item(name: "Name3")]
func index(of item: Item) -> Int {
items.firstIndex { $0.id == item.id } ?? -1
}
var body: some View {
VStack {
ForEach(items, id: \.id) { item in
// separate dependent views as much as possible to make them as
// smaller/lighter as possible
ItemRowView(items: self.$items, index: self.index(of: item))
}
}
}
}
struct ItemRowView: View {
#Binding var items: [Item]
let index: Int
#State private var destroyed = false // internal state to validate self
var body: some View {
// proxy binding to have possibility for validation
let binding = Binding(
get: { self.destroyed ? "" : self.items[self.index].name },
set: { self.items[self.index].name = $0 }
)
return HStack {
if !destroyed { // safety check against extra update
TextField("name", text: binding)
Button( action: {
self.destroyed = true
self.$items.wrappedValue.remove(at: self.index)
}) {
Text("Delete")
}
}
}
}
}
Yes, it is not easy solution, but sometimes there are situations we need it.