SwiftUI列表+ Firebase Firestore，获取数据然后再取消获取？(错误)

import SwiftUI
import Firebase

struct ContentView: View {
    @ObservedObject var dataModel = FirestoreDataModel()
    
    var body: some View {
        List(dataModel.items) { item in
            Text(item.name)
        }
        .onAppear {
            dataModel.loadData()
        }
    }
}

class FirestoreDataModel: ObservableObject {
    @Published var items: [Item] = []
    private var listener: ListenerRegistration?
    
    func loadData() {
        let db = Firestore.firestore()
        listener = db.collection("items").addSnapshotListener { querySnapshot, error in
            guard let documents = querySnapshot?.documents else {
                print("Error fetching documents: \(error!)")
                return
            }
            
            self.items = documents.map { document in
                let data = document.data()
                let name = data["name"] as? String ?? ""
                return Item(name: name)
            }
        }
    }
}

struct Item: Identifiable {
    let id = UUID()
    let name: String
}