ios - SwiftUI - How to pass EnvironmentObject into View Model?

Question

I'm looking to create an EnvironmentObject that can be accessed by the View Model (not just the view).

The Environment object tracks the application session data, e.g. loggedIn, access token etc, this data will be passed into the view models (or service classes where needed) to allow calling of an API to pass data from this EnvironmentObjects.

I have tried to pass in the session object to the initialiser of the view model class from the view but get an error.

how can I access/pass the EnvironmentObject into the view model using SwiftUI?

Answer 1

Below provided approach that works for me. Tested with many solutions started with Xcode 11.1.

The problem originated from the way EnvironmentObject is injected in view, general schema

SomeView().environmentObject(SomeEO())

ie, at first - created view, at second created environment object, at third environment object injected into view

Thus if I need to create/setup view model in view constructor the environment object is not present there yet.

Solution: break everything apart and use explicit dependency injection

Here is how it looks in code (generic schema)

// somewhere, say, in SceneDelegate

let someEO = SomeEO()                            // create environment object
let someVM = SomeVM(eo: someEO)                  // create view model
let someView = SomeView(vm: someVM)              // create view 
                   .environmentObject(someEO)

There is no any trade-off here, because ViewModel and EnvironmentObject are, by design, reference-types (actually, ObservableObject), so I pass here and there only references (aka pointers).

class SomeEO: ObservableObject {
}

class BaseVM: ObservableObject {
    let eo: SomeEO
    init(eo: SomeEO) {
       self.eo = eo
    }
}

class SomeVM: BaseVM {
}

class ChildVM: BaseVM {
}

struct SomeView: View {
    @EnvironmentObject var eo: SomeEO
    @ObservedObject var vm: SomeVM

    init(vm: SomeVM) {
       self.vm = vm
    }

    var body: some View {
        // environment object will be injected automatically if declared inside ChildView
        ChildView(vm: ChildVM(eo: self.eo)) 
    }
}

struct ChildView: View {
    @EnvironmentObject var eo: SomeEO
    @ObservedObject var vm: ChildVM

    init(vm: ChildVM) {
       self.vm = vm
    }

    var body: some View {
        Text("Just demo stub")
    }
}