ios - 如何从 Firestore 返回数组中的数据？

Question

我正在构建一个 IOS 应用程序，我正处于要在 pickerview 中加载一些类别的阶段。类别列表作为文档存储在 Firestore 中。

我有一个函数可以执行以下操作:

1. 初始化数组
2. 从 Firestore 读取数据
3. 在数组中附加值
4. 返回数组

问题是函数似乎返回了数组，甚至没有从 Firestore 获得任何结果

我的数据模型

class categoryModel {
    var catImg=""
    var catName=""
    var catID=""
    //set categories
    init(catImg: String, catName:String, catID:String){
        self.catName=catName
        self.catImg=catImg
        self.catID=catID
    }
}

Firestore 引用

struct FirestoreReferenceManager {

    static let event = "events"

    static let db = Firestore.firestore()
    static let rootEvents = db.collection("events")
    static let rootUsers = db.collection("users")

}

Firestore 服务

class FirestoreService {

    static func getCategoryfromDB()->[categoryModel] {

        let rootCategory = FirestoreReferenceManager.rootEvents
        var tabCategory=[categoryModel]()


        rootCategory.getDocuments() { (querySnapshot, err) in
            if let err = err {
                print("Error getting documents: \(err)")
            } else {
                for document in querySnapshot!.documents {

                    tabCategory.append(categoryModel(catImg: document.data()["img"] as! String, catName:document.data()["name"] as! String, catID: document.documentID))

                    print("number of categories running: \(tabCategory.count)")
                }
            }

        }
        print("number of categories final: \(tabCategory.count)")
        return tabCategory
    }
}

检查日志显示的内容

umber of categories final: 0
number of categories final: 0
number of categories running: 1
number of categories running: 2
number of categories running: 3
number of categories running: 4
number of categories running: 5
number of categories running: 6
number of categories running: 7
number of categories running: 8
number of categories running: 9
number of categories running: 10
number of categories running: 11
number of categories running: 1
number of categories running: 2
number of categories running: 3
number of categories running: 4
number of categories running: 5
number of categories running: 6
number of categories running: 7
number of categories running: 8
number of categories running: 9
number of categories running: 10
number of categories running: 11

前两行实际上应该是最后一行。

当我从 View Controller 读取 Firestore 时，数组为空。我尝试对数据模型进行硬编码，它工作正常。

我读到有关获取数据的一些“延迟”，但是如何解决这个问题？

我该如何解决这个问题？

Answer 1

像这样的东西应该可以做到。dispatch 是一个可以添加闭包的组。一旦所有这些都完成，就会调用通知闭包，您可以在其中返回数据。阅读调度组，这将有所帮助。

static func getCategoryfromDB(completed: @escaping ([categoryModel]) -> Void) {

        let rootCategory = FirestoreReferenceManager.rootEvents
        var tabCategory=[categoryModel]()
        let dispatch = DispatchGroup()
        dispatch.enter()
        rootCategory.getDocuments() { (querySnapshot, err) in
            if let err = err {
                print("Error getting documents: \(err)")
            } else {
                for document in querySnapshot!.documents {

                    tabCategory.append(categoryModel(catImg: document.data()["img"] as! String, catName:document.data()["name"] as! String, catID: document.documentID))

                    print("number of categories running: \(tabCategory.count)")
                }
            }
            dispatch.leave()

        }
        dispatchGroup.notify(queue: .main, execute: {
            print("number of categories final: \(tabCategory.count)")
            completed(tabCategory)

        })


        }