SwiftUI: Must an ObservableObject be passed into a View as an EnvironmentObject? - swiftui

Question

If I create an ObservableObject with a #Published property and inject it into a SwifUI view with .environmentObject(), the view responds to changes in the ObservableObject as expected.
class CounterStore: ObservableObject {
#Published private(set) var counter = 0
func increment() {
counter += 1
}
}
struct ContentView: View {
#EnvironmentObject var store: CounterStore
var body: some View {
VStack {
Text("Count: \(store.counter)")
Button(action: { store.increment() }) {
Text("Increment")
}
}
}
}
Tapping on "Increment" will increase the count.
However, if I don't use the EnvironmentObject and instead pass the store instance into the view, the compiler does not complain, the store method increment() is called when the button is tapped, but the count in the View does not update.
struct ContentViewWithStoreAsParameter: View {
var store: CounterStore
var body: some View {
VStack {
Text("Count: \(store.counter) (DOES NOT UPDATE)")
Button(action: { store.increment() }) {
Text("Increment")
}
}
}
}
Here's how I'm calling both Views:
#main
struct testApp: App {
var store = CounterStore()
var body: some Scene {
WindowGroup {
VStack {
ContentView().environmentObject(store) // works
ContentViewWithStoreAsParameter(store: store) // broken
}
}
}
}
Is there a way to pass an ObservableObject into a View as a parameter? (Or what magic is .environmentalObject() doing behind the scenes?)

Answer 1

It should be observed somehow, so next works
struct ContentViewWithStoreAsParameter: View {
#ObservedObject var store: CounterStore
//...

Answer 2

You can pass down your store easily as #StateObject:
#main
struct testApp: App {
#StateObject var store = CounterStore()
var body: some Scene {
WindowGroup {
VStack {
ContentView().environmentObject(store) // works
ContentViewWithStoreAsParameter(store: store) // also works
}
}
}
}
struct ContentViewWithStoreAsParameter: View {
#StateObject var store: CounterStore
var body: some View {
VStack {
Text("Count: \(store.counter)") // now it does update
Button(action: { store.increment() }) {
Text("Increment")
}
}
}
}
However, the store should normally only be available for the views that need it, why this solution would make the most sense in this context:
struct ContentView: View {
#StateObject var store = CounterStore()
var body: some View {
VStack {
Text("Count: \(store.counter)")
Button(action: { store.increment() }) {
Text("Increment")
}
}
}
}