When exactly SwiftUI releases ObservableObjects - swift

Question

I am trying to learn how SwiftUI works internally in terms of memory management. I have little doubt about it.
When I add a NavigationLink to the 2nd View which has some Search Functionality and also loading some data from the cloud.
Now when I came back to the root view, my observableObject class is still in memory.
Does anyone have any idea how SwiftUI manages the memory and release objects?
Here is a sample code of my experiment.
struct ContentView: View {
var body: some View {
NavigationView {
DemoView(screenName: "Home")
.navigationBarHidden(true)
}
}
}
struct DemoView:View {
var screenName:String
var body: some View {
VStack{
NavigationLink(destination: SecondView(viewModel:SecondViewModel())) {
Text("Take Me To Second View")
}
Text(self.screenName)
}
}
}
// Second View
class SecondViewModel:ObservableObject {
#Published var search:String = ""
#Published var user:[String] = []
func fetchRecords() -> Void {
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 3) { [weak self] in
self?.user = ["Hello", "There"]
}
}
}
struct SecondView:View {
#ObservedObject var viewModel:SecondViewModel
var body: some View {
VStack {
TextField("Search Here", text: $viewModel.search)
.textFieldStyle(RoundedBorderTextFieldStyle())
.padding()
List(self.viewModel.user, id:\.self) { user in
Text("User \(user)")
}
}.onAppear{
self.viewModel.fetchRecords()
}
}
}
And this is what I received in-memory graph.

Answer 1

The object lifecycle in SwiftUI is as usual. An object is deallocated by ARC when there are no more references to it. You can add deinit { print("deinit")}
to your SecondViewModel and see when the object is deallocated. And yes, in your case a new SecondViewModel object will be created each time the DemoView body is evaluated, which is probably not what you want. I guggest you initialize and store the SecondViewModel object outside of the view hierarchy, and pass a reference to this global object in DemoView.body .

Answer 2

Ok, I probably don't remember other similar post on the same issue, but the reason of it because your SecondView, cause it is a value, still is in NavigationView when you press back, as long as until another NavigationLink is activated.
So you need either to have different independent life-cycle for SecondViewModel or, if remain as-is, to add some reset/cleanup for it, so only pure empty object left, ie
}.onAppear{
self.viewModel.fetchRecords()
}.onDisappear {
self.viewModel.cleanup()
}