Create a custom AsyncSequence - json

Question

NOTE: Currently config: Xcode 13 beta 3 (13A5192i), macOS Montery (21A5284e).
Trying to asynchronously initialize data from a json.
The code apparently works fine, but the elements are not added to #Published public private (set) var users = [User]()
Is it something stupid I don't see or is it just another bug?
[
{
"id": 1,
"name":"gio"
},
{
"id": 3,
"name":"mimi"
},
{
"id": 2,
"name":"pepo"
},
{
"id": 4,
"name":"bassix"
},
{
"id": 5,
"name":"peponews"
}
]
import SwiftUI
struct URLWatcher: AsyncSequence, AsyncIteratorProtocol {
typealias Element = Data
let url: URL
let delay: Int
private var comparisonData: Data?
init(url: URL, delay: Int = 10) {
self.url = url
self.delay = delay
}
mutating func next() async throws -> Data? {
if comparisonData == nil {
comparisonData = try await fetchData()
} else {
while true {
await Task.sleep(UInt64(delay) * 1_000_000_000)
let latestData = try await fetchData()
if latestData != comparisonData {
comparisonData = latestData
break
}
}
}
if comparisonData == nil {
return nil
} else {
return comparisonData
}
}
private func fetchData() async throws -> Data {
let (data, _) = try await URLSession.shared.data(from: url)
return data
}
func makeAsyncIterator() -> URLWatcher {
self
}
}
struct User: Identifiable, Decodable {
let id: Int
let name: String
}
#MainActor
class UserData: ObservableObject {
static let shared = UserData()
#Published public private(set) var users = [User]()
func fetchUsers() async {
let url = Bundle.main.url(forResource: "items", withExtension: "json")
let urlWatcher = URLWatcher(url: url!, delay: 3)
do {
for try await data in urlWatcher {
try withAnimation {
let data = try JSONDecoder().decode([User].self, from: data)
print(data)
users = data
}
}
} catch {
print("error \(error)")
}
}
private init() {
// Begin loading the data
Task {
await fetchUsers()
}
}
}
struct TestAsync: View {
let data = UserData.shared
var body: some View {
List(data.users) { user in
Text(user.name)
}
}
}

Answer 1

try this:
struct TestAsync: View {
#StateObject var data = UserData.shared // <-- or #ObservedObject
var body: some View {
List(data.users) { user in
Text(user.name)
}
}
}