错误：无法将“CueCardModel”类型的值转换为闭包结果类型“Void”SwiftUI

Question

I am trying to make a Cue Card App. I have my DataDownloader class put my Firebase Database into an array, which the array passes to my CueCardViewModel, that returns a term and answer from a specific index to my CueCardView.

Confusing...so basically, the CueCardView should be able to call on the CueCardViewModel to get a term and answer at a specific index from the DataDownloader class. The problem I am having is the CueCardViewModel won't return. I am new to Swift and have tried searching for a way to do this, but I am confused because most videos/forums seem to be hardcoding their database so I am having trouble.

CueCardView:

import SwiftUI

struct CueCardView: View
{
var viewModel = CueCardViewModel()
@State private var isShowingAnswer = false
var body: some View
{
    ZStack
    {
        RoundedRectangle(cornerRadius: 25, style: .continuous)
            .fill(Color.white)
        VStack
        {
            var a = getCue()
            Text(a)
                .onAppear
                {
                    self.viewModel.initializeCues(index: 1)
                }
        }
        .padding(20)
        .multilineTextAlignment(.center)
    }
    .onTapGesture
    {
        self.isShowingAnswer.toggle()
    }
  }
}

extension CueCardView {
func getCue() -> String{
    return "BBBBBBB"
 }
}
struct C1_Previews: PreviewProvider {
static var previews: some View {
    CueCardView().previewDevice("iPhone 12")
 }
}    

CueCardModel:

import SwiftUI

struct CueCardModel : Identifiable {
  var id: String = UUID().uuidString
  var term: String
  var answer: String
}

DataDownloader:

import SwiftUI
import Firebase

var dbRef = Firestore.firestore()
struct DataDownloader {
  func downloadCues(completion: @escaping ([CueCardModel]) -> Void) {
    var array = [CueCardModel]()
    dbRef.collection("Cue").getDocuments(){(snap, err) in
        if let err = err {
            print(err)
        } else {
            guard let snap = snap else {return}
            for doc in snap.documents {
                let id = doc.documentID
                let term = doc.get("term") as! String
                let answer = doc.get("answer") as! String
                let cue = CueCardModel(id: id, term: term, answer: answer)
                array.append(cue)
            }
            completion(array)
        }
    }
  }
}

CueCardViewModel:

import SwiftUI
import Firebase

class CueCardViewModel: ObservableObject {

let dataDownloader = DataDownloader()


func initializeCues(index :Int) -> [CueCardModel] {
    dataDownloader.downloadCues{array in
        return array[0]
    }
 }
}

Answer 1

initializeCues needs to be an @escaping closure similar to your downloadCues function. When you're downloading the data, it will take some time to get the info from the database and return.. therefore you can't just 'return' immediately.