SwiftUI update a view with custom object property change - swiftui

Question

I in the process of converting my application to SwiftUI but have encountered a problem. I know what the root cause is but can’t seem to figure out how to work around it.
I am using Parse live queries to update my ViewModel which contains an array of custom objects. Everything works as expected when adding/removing objects from the server the UI updates as expected however when I am trying to update an object parameter the UI doesn’t reflect the change although the object updates successfully in the ViewModel.
The code below is a simplified version of my code but shows the issue.
Hopefully someone can shed some light or point me to the right direction.
struct Candidate : ParseObject, Equatable {
static func == (lhs: ParseCandidate, rhs: ParseCandidate) -> Bool {
return lhs.objectId == rhs.objectId
} // <- I believe this is causing the issue
var objectId : String?
var name : String?
var status : String?
}
class CandidatesViewModel : ObservableObject {
#Published candidatesList = [Candidates]()
init() {
//1. get objects from server
//2. subscribe to live queries
}
// this method get called when an update is received from the server
func updateCandiate(_ candidate : Candidate) {
if let index = candidatesList.first(where: {$0 == candidate}) {
candidatesList[index] = candidate
}
}
}
struct CandidateListView : View {
#StateObject var viewModel = CandidatesViewModel()
var body: some View {
LazyVGrid(columns: [GridItem(.adaptive(minimum: 180,maximum: 180),spacing: 20) ], alignment: .leading, spacing: 30, pinnedViews: [.sectionHeaders]) {
Section {
ForEach(viewModel.candidatesList, id: \.self){ candidate in
CandidateCard(candidate: candidate)
}
}header: {
Text("Header")
}.padding(.horizontal)
}
}
}
struct CandidateCardView : View {
let candidate : Candidate
var body : some View {
VStack{
Text(candidate.name!)
Text(candidate.status!)
}
}
}
I have noticed if I removed the equatable a new instance gets added to the array as swift assumes its a new object because all properties have to match.
the only way to reflect the update so far is if I make the candidate inside the CandidateCardView #Binding then the update is reflected but seems unnecessary and complicates things.
Any guidance is highly appreciated.

Answer 1

SwiftUI uses Equatable conformance to determine whether an object has changed. In your case, you're using the objectId to determine equality, so it won't register as updated when an different field changes. To update when another property changes, include that in the ==, or just use the synthesised version, which includes all properties. You should also make it Identifiable
struct Candidate : ParseObject, Equatable, Identifiable {
var id: String { objectId ?? UUID().uuidString }
var objectId : String? // Can this _really_ be nil?
var name : String?
var status : String?
}
In that case, in updateCandiate you'll need to update to {$0.objectId == candidate.objectId}
class CandidatesViewModel : ObservableObject {
#Published candidatesList = [Candidates]()
// this method get called when an update is received from the server
func updateCandiate(_ candidate : Candidate) {
if let index = candidatesList.first(where: {$0.objectId == candidate.objectId}) {
candidatesList[index] = candidate
}
}
}
and now Candidate is Identifiable
struct CandidateListView : View {
#StateObject var viewModel = CandidatesViewModel()
var body: some View {
LazyVGrid(columns: [GridItem(.adaptive(minimum: 180,maximum: 180),spacing: 20) ], alignment: .leading, spacing: 30, pinnedViews: [.sectionHeaders]) {
Section {
ForEach(viewModel.candidatesList){ candidate in
CandidateCard(candidate: candidate)
}
}header: {
Text("Header")
}.padding(.horizontal)
}
}
}