SwiftUI simple Pop-Up Alert from a function in a class

Question

I am a little confused, I try to display a pop-up in my View when my function is true otherwise continue but I do not understand how to do it I am lost between the different ways of doing. I tried several things but something escapes me.

Edit: The project is based on SwiftUI and the popup as to be displayed in a SwiftUI View, the function is in a class returning an ObservableObject. The function is called from a SwiftUI View from a button.

get_deliveries.swift -> into a class delivViewModel:ObservableObject

    func cancelDeliv(delivID: String) {
        let delivRef = db.collection("av_deliveries").document(delivID)
        let isDemain = Date().dayAfter.toString()
        delivRef.getDocument { (document, error) in
            if let document = document, document.exists {
                let property = document.get("when")
                if isDemain == property as! String {
                      // Print a pop-up error
                } else {
                delivRef.updateData([
                    "taken": false,
                    "taken_by": ""
                ]) { err in
                    if let err = err {
                        print("Error updating document: \(err)")
                    } else {
                        print("Document successfully updated")
                    }
                }
            }
            }
        }
    }

Answer 1

Here is a basic demo of activating an alert with a Button in a View body from an ObservableObject class.

struct ContentView: View {
// However you've initialized your class, it may be different than this.
@StateObject var progress = DeliveriesViewModel()

var body: some View {
    VStack  {
    // Other views in your View body

        // SwiftUI button to activate the Bool in ObservableObject class.
        Button {
            progress.isDisplayingAlert.toggle()
        } label: {
            Text("Toggle Alert")
        }
    }
    .alert(isPresented: $progress.isDisplayingAlert) { () -> Alert in
        Alert(title: Text("Alert Title"), message: Text("Body of Alert."), dismissButton: .cancel())
    }
  }
}

class DeliveriesViewModel: ObservableObject {

@Published var isDisplayingAlert = false

func displayAlert() {
    // other function actions...
    
    // update Published property.
    isDisplayingAlert = true
 
    // other function actions...
  }
}