SwiftUI: Passing an environmentObject to a sheet causes update problems - swiftui

Question

If you want to pass an #EnvironmentObject to a View presented as a sheet, you'll notice that this sheet gets recreated every single time any #Published property in the #EnvironmentObject is updated.
Minimum example that demonstrates the problem:
import SwiftUI
class Store: ObservableObject {
#Published var name = "Kevin"
#Published var age = 38
}
struct ContentView: View {
#EnvironmentObject private var store: Store
#State private var showProfile = false
var body: some View {
VStack {
Text("Hello, \(store.name), you're \(store.age) years old")
Button("Edit profile") {
self.showProfile = true
}
}
.sheet(isPresented: $showProfile) {
ProfileView()
.environmentObject(self.store)
}
}
}
struct ProfileView: View {
#EnvironmentObject private var store: Store
#ObservedObject private var viewModel = ViewModel()
var body: some View {
VStack {
Text("Hello, \(store.name), you're \(store.age) years old")
Button("Change age") {
self.store.age += 1
}
}
}
}
class ViewModel: ObservableObject {
init() {
print("HERE")
}
}
If you run this code, you'll notice that "HERE" gets logged every single time you press the button in the sheet, meaning that the ViewModel got recreated. This can be a huge problem as you might imagine, I expect the ViewModel to not get recreated but retain its state. It's causing huge problems in my app.
As far as I am aware, what I am doing in my code is the normal way to pass the #EnvironmentObject to a sheet. Is there a way to prevent the ProfileView from getting recreated any time something in the Store changes?

Answer 1

This is because the view gets recreated when a state variable changes. And in your view you instantiate the viewModel as ViewModel().
Try passing the observed object as a param and it won't hit "HERE" anymore:
struct ContentView: View {
#EnvironmentObject private var store: Store
#State private var showProfile = false
#ObservedObject private var viewModel = ViewModel()
var body: some View {
VStack {
Text("Hello, \(store.name), you're \(store.age) years old")
Button("Edit profile") {
self.showProfile = true
}
}
.sheet(isPresented: $showProfile) {
ProfileView(viewModel: self.viewModel)
.environmentObject(self.store)
}
}
}
struct ProfileView: View {
#EnvironmentObject private var store: Store
#ObservedObject var viewModel: ViewModel
var body: some View {
VStack {
Text("Hello, \(store.name), you're \(store.age) years old")
Button("Change age") {
self.store.age += 1
}
}
}
}

Answer 2

If your Deployment Target is iOS14 and above, have you tried replacing #ObservedObject with #StateObject in ProfileView? This will help in keeping the state, it will only be created once, even if the Model View instantiaton happens inside the View's body.

Answer 3

A very nice article about this issue can be found her.