Can't access class variables besides from in SwiftIU view - swift

Question

So I'm trying to access my data by id using a url such as http://localhost:8000/albums/whateverid.
First I gain the ids
class Webservice {
func getAllPosts(completion: #escaping ([Post]) -> ()) {
guard let url = URL(string: "http://localhost:8000/albums")
else {
fatalError("URL is not correct!")
}
URLSession.shared.dataTask(with: url) { data, _, _ in
let posts = try!
JSONDecoder().decode([Post].self, from: data!); DispatchQueue.main.async {
completion(posts)
}
}.resume()
}
}
struct Post: Codable, Hashable, Identifiable {
let id: String
let title: String
let path: String
let description: String
}
Set the variables to the data from class Webservice
final class PostListViewModel: ObservableObject {
init() {
fetchPosts()
}
#Published var posts = [Post]()
private func fetchPosts() {
Webservice().getAllPosts {
self.posts = $0
print("posts \(self.posts)")
}
}
}
And this is how I'm trying to grab album by id by using the id I fetched from the code above
I create a class that when a id is inserted will give me the album data back by id
class SecondWebService: Identifiable {
var id:String = ""
init(id: String?) {
self.id = id!
}
func getAllPostsById(completion: #escaping ([PostById]) -> ()) {
guard let url = URL(string: "http://localhost:8000/albums/\(id)")
else {
fatalError("URL is not correct!")
}
URLSession.shared.dataTask(with: url) { data, _, _ in
let posts = try!
JSONDecoder().decode([PostById].self, from: data!); DispatchQueue.main.async {
completion(posts)
}
}.resume()
}
}
Variables
struct PostById: Codable, Hashable, Identifiable {
let id: String
let name: String?
let path: String
}
Here's where I try to insert the id from class PostListViewModel into my class SecondWebService to get the data back set my variables to that data
final class PostListViewByIdModel: ObservableObject {
#ObservedObject var model = PostListViewModel()
init() {
fetchPostsById()
}
#Published var postsById = [PostById]()
private func fetchPostsById() {
for post in model.posts {
SecondWebService(id: post.id).getAllPostsById {
self.postsById = $0
print("postById \(post)")
}
}
}
}
For some reason above when I try to print nothing will display because I believe posts in model.posts isn't getting read
When I use it here in List() it works but not in init:
struct ContentView: View {
#ObservedObject var model = PostListViewModel()
init() {
for post in model.posts {
print(post)
}
}
var body: some View {
NavigationView {
List(model.posts) { post in
VStack{
Text("Title: ").bold()
+ Text("\(post.title)")
NavigationLink(destination: Album(post: post)) {
ImageView(withURL: "http://localhost:8000/\(post.path.replacingOccurrences(of: " ", with: "%20"))")
}
Text("Description: ").bold()
+ Text("\(post.description)")
}
}
}
}
}
I'm very curious on why nothing is printing when I use model.posts in my for loop. Only when I use it in the SwiftUI functions does it work.

Answer 1

I'm very curious on why nothing is printing when I use model.posts in my for loop
It is because of asynchronous nature of the following call
private func fetchPosts() {
Webservice().getAllPosts {
so in init
#ObservedObject var model = PostListViewModel() // just created
init() {
for post in model.posts { // posts are empty because
// `Webservice().getAllPosts` has not finished yet
print(post)
}
Update: You need to call second service after first one got finished, here is possible approach (only idea - cannot test)
struct ContentView: View {
#ObservedObject var model = PostListViewModel()
#ObservedObject var model2 = PostListViewByIdModel()
// delete init() - it is not needed here
...
var body: some View {
NavigationView {
List(model.posts) { post in
...
}
.onReceive(model.$posts) { posts in // << first got finished
self.model2.fetchPostsById(for: posts) // << start second
}
.onReceive(model2.$postsById) { postById in
// do something here
}
}
}
and updated second service
final class PostListViewByIdModel: ObservableObject {
#Published var postsById = [PostById]()
func fetchPostsById(for posts: [Post]) { // not private now
for post in model.posts {
SecondWebService(id: post.id).getAllPostsById {
self.postsById = $0
print("postById \(post)")
}
}