SwiftUI Error Regarding Publishing Changes from Background Thread - swiftui

Question

I am not quite sure how to fix an error that appears three times in my View Model:
import SwiftUI
class GHViewModel: ObservableObject {
let columns: [GridItem] = [
GridItem(.flexible()),
GridItem(.flexible()),
GridItem(.flexible())
]
#Published var followers: [Follower] = []
#Published var page = 1
#Published var user: User = PlaceholderData.user
#Published var networkError: GFError = .invalidURL
#Published var shouldShowNetworkError = false
#Published var shouldShowFollowerDetails = false
func getFollowers(userID: String) {
NetworkManager.shared.getFollowers(for: userID, page: self.page) { result in
switch result {
case .success(let followers):
if !followers.isEmpty {
self.followers += followers
print("**** GHViewModel -> FollowersScreen has retrieved the followers. I see \(self.followers.count) followers for this user.")
}
case .failure(let error):
self.shouldShowNetworkError = true
self.networkError = error
}
}
}
func getFollowerDetails(userID: String) {
NetworkManager.shared.getUserInfo(for: userID) { result in
switch result {
case .success(let ghUser):
self.user = ghUser
self.shouldShowFollowerDetails = true
case .failure(let error):
self.shouldShowNetworkError = true
self.networkError = error
}
}
}
}
The 3 warnings are happening at:
#Published var followers: [Follower] = []
and..
case .success(let ghUser):
self.user = ghUser
self.shouldShowFollowerDetails = true
What is this error actually saying? I suppose it's suggesting that I should be using
DispatchQueue.main.async { // code here }
around the code that's generating the warnings?
Please advise?

Answer 1

Yes, it is telling your to use DispatchQueue.main.async. Remember, network calls are asynchoronous. You don't know when you are getting a response, so they are automatically performed on a background thread, but you always need to update your data that is being displayed on your main thread. Therefore, every time you hit .success, you need to update the variables on the main thread by enclosing the updates in DispatchQueue.main.async.
case .success(let followers):
if !followers.isEmpty {
DispatchQueue.main.async {
self.followers += followers
print("**** GHViewModel -> FollowersScreen has retrieved the followers. I see \(self.followers.count) followers for this user.")
}
}
and
case .success(let ghUser):
DispatchQueue.main.async {
self.user = ghUser
self.shouldShowFollowerDetails = true
}
I suspect the #Published error will go away as I suspect that is thrown due to the other issues.