Google cloud firestore DispatchQUE获取firestore数据，但不'；t填充阵列

这是我的第一个SwiftUI应用程序。我一直在阅读开发者信息和教程，但是我找不到我想要做的事情

这是一个图书馆应用程序，可以通过两种方式访问图书信息

搜索字段->尚未搜索

描述书的特点

我正在使用Firestore文档处理第二个

我可以获得第一个列表（作者），并保存选定的作者。当我试图使用firestorm文档访问第二个描述列表（类型）时，问题就开始了。 DispatchQueue无法正常工作，因为它可以获取文档信息，但无法填充数组，因此始终发送空数组[]。如果我创建了数组genreItems并忽略了查询，那么类型列表就完美了。此外，如果我使用自动选择，firestore查询不会得到响应

我不确定我的发展方式，也许有一个简单的方法。 希望我解释正确

这是数据库模型

import Foundation

struct DataBookModel: Hashable, Codable, Identifiable {

    var id : Int
    var dataBookModelString : String
    
}

用于选择作者的第一个列表为Array->

import Foundation
import SwiftUI

var AuthorsItems = [

    DataBookModel(id: 1, dataBookModelString: "Stephen King"),
    DataBookModel(id: 2, dataBookModelString: "Isaac Asimov"),
    DataBookModel(id: 3, dataBookModelString: "Michael Cripton"),
    DataBookModel(id: 4, dataBookModelString: "Anne Rice")
    
    ]

列表行

import Foundation
import SwiftUI

struct ItemsRow: View {
    
    var dataBookModel : DataBookModel
    
    var body: some View {
        Text(dataBookModel.dataBookModelString)
    }
}

作者

import Foundation
import SwiftUI

struct AuthorsList: View {
    
    var body: some View {
        VStack{
            Text("Selecy author")
            List(AuthorsItems){
                item in
                NavigationLink(destination: GenreList(dataBookModel: item)){
                    ItemsRow(dataBookModel: item)
                }
            }
        }
    }
}

第二个列表->GenreList

import Foundation
import SwiftUI
import FirebaseFirestore
import FirebaseFirestoreSwift
import Combine

struct GenreList : View {
    
    var dataBookModel : DataBookModel
    
    @ObservedObject var genreItems = GenreItems()
    
    func saveAuthor() {
        let selectedAuthor = String(dataBookModel.dataBookModelString)
        if !selectedAuthor.isEmpty {
            UserDefaults.standard.set(selectedAuthor, forKey: "selectedAuthor")
            print("saved author: \(selectedAuthor)")
        } else {
            print("error: no author selected")
        }
    }
    
    var body: some View {
        VStack {
            Text("Select Genre")
            
            List(self.genreItems.genreItems) {
                item in
                ItemsRow(dataBookModel: item)
            }
            
        }.onAppear(){
            print("genreList: \(self.genreItems.genreItems)")
            
            self.saveAuthor()
            
        }
    }
}

import Foundation
import SwiftUI
import FirebaseFirestore
import Combine

class GenreItems: ObservableObject {
    
    @Published var genreItems = [DataBookModel]()
    
    init() {
        
        print("memoria: \(self.genreItems)")
    /*
        genreItems = [
            DataBookModel(id: 1, dataBookModelString: "Science fiction"),
            DataBookModel(id: 2, dataBookModelString: "Comedy"),
            DataBookModel(id: 3, dataBookModelString: "Terror")
        ]
       */
        let selectedAuthor = UserDefaults.standard.value(forKey: "selectedAuthor")
        print("saved author GenreItems: \(selectedAuthor)")
        
        var db : Firestore!
        db = Firestore.firestore()
        
        db.collection("genres")
            //.whereField("author", isEqualTo: selectedAuthor!)
            .getDocuments(){
                (querySnapshot, error) in
                if let error = error {
                    print("Error en documentos: \(error.localizedDescription)")
                } else {
                    var i = 0
                    for document in querySnapshot!.documents {
                        let valor = document.data()
                        print("búsqueda: \(valor)")
                        let genre = document.get("genre") as? String ?? "sin genre"
                        i += 1
                        let id = i
                        
                        DispatchQueue.main.async {
                            let registro = DataBookModel(id: i, dataBookModelString: genre)
                            print("registro: \(registro)")
                            self.genreItems.append(registro)
                            print("genreItems: \(self.genreItems)")
                        }
                    }
                    print("result: \(self.genreItems)")
                }
                
        }
        
        
    }
}

流派项目创建->流派列表

import Foundation
import SwiftUI
import FirebaseFirestore
import FirebaseFirestoreSwift
import Combine

struct GenreList : View {
    
    var dataBookModel : DataBookModel
    
    @ObservedObject var genreItems = GenreItems()
    
    func saveAuthor() {
        let selectedAuthor = String(dataBookModel.dataBookModelString)
        if !selectedAuthor.isEmpty {
            UserDefaults.standard.set(selectedAuthor, forKey: "selectedAuthor")
            print("saved author: \(selectedAuthor)")
        } else {
            print("error: no author selected")
        }
    }
    
    var body: some View {
        VStack {
            Text("Select Genre")
            
            List(self.genreItems.genreItems) {
                item in
                ItemsRow(dataBookModel: item)
            }
            
        }.onAppear(){
            print("genreList: \(self.genreItems.genreItems)")
            
            self.saveAuthor()
            
        }
    }
}

import Foundation
import SwiftUI
import FirebaseFirestore
import Combine

class GenreItems: ObservableObject {
    
    @Published var genreItems = [DataBookModel]()
    
    init() {
        
        print("memoria: \(self.genreItems)")
    /*
        genreItems = [
            DataBookModel(id: 1, dataBookModelString: "Science fiction"),
            DataBookModel(id: 2, dataBookModelString: "Comedy"),
            DataBookModel(id: 3, dataBookModelString: "Terror")
        ]
       */
        let selectedAuthor = UserDefaults.standard.value(forKey: "selectedAuthor")
        print("saved author GenreItems: \(selectedAuthor)")
        
        var db : Firestore!
        db = Firestore.firestore()
        
        db.collection("genres")
            //.whereField("author", isEqualTo: selectedAuthor!)
            .getDocuments(){
                (querySnapshot, error) in
                if let error = error {
                    print("Error en documentos: \(error.localizedDescription)")
                } else {
                    var i = 0
                    for document in querySnapshot!.documents {
                        let valor = document.data()
                        print("búsqueda: \(valor)")
                        let genre = document.get("genre") as? String ?? "sin genre"
                        i += 1
                        let id = i
                        
                        DispatchQueue.main.async {
                            let registro = DataBookModel(id: i, dataBookModelString: genre)
                            print("registro: \(registro)")
                            self.genreItems.append(registro)
                            print("genreItems: \(self.genreItems)")
                        }
                    }
                    print("result: \(self.genreItems)")
                }
                
        }
        
        
    }
}