我从 Firestore 读取了一个文档，不知何故我调用了我的 get() 函数两次。我不知道为什么[关闭]

Question

我从 firestore 文档中的以下代码开始，只更改了变量名称等...

    private func customClassGetDocument() {
    // [START custom_type]
    let docRef = db.collection("cities").document("BJ")

    docRef.getDocument { (document, error) in
        // Construct a Result type to encapsulate deserialization errors or
        // successful deserialization. Note that if there is no error thrown
        // the value may still be `nil`, indicating a successful deserialization
        // of a value that does not exist.
        //
        // There are thus three cases to handle, which Swift lets us describe
        // nicely with built-in Result types:
        //
        //      Result
        //        /\
        //   Error  Optional<City>
        //               /\
        //            Nil  City
        let result = Result {
          try document?.data(as: City.self)
        }
        switch result {
        case .success(let city):
            if let city = city {
                // A `City` value was successfully initialized from the DocumentSnapshot.
                print("City: \(city)")
            } else {
                // A nil value was successfully initialized from the DocumentSnapshot,
                // or the DocumentSnapshot was nil.
                print("Document does not exist")
            }
        case .failure(let error):
            // A `City` value could not be initialized from the DocumentSnapshot.
            print("Error decoding city: \(error)")
        }
    }

这是我的代码。首先，一个简单的自定义对象。 myFriends 数组是我从 firestore 读取的单个文档中加载的。

struct Friends: Identifiable, Hashable, Codable {
    
    @DocumentID var id: String?   
    var myFriends: [String] = []
   
}

这是我的类，我在其中定义了一个存储库来管理我的朋友对象。 （获取、添加、更新等）

class FriendRepository: ObservableObject {
    
    private    let store = Firestore.firestore()
    private    let friendPath: String = "MyFriends"
    @Published var friendIDs: [String] = []

    var userId = ""
    
    private let authenticationService = AuthenticationService()
    private var cancellables: Set<AnyCancellable> = []
    
    init() {
        authenticationService.$user
            .compactMap { user in
                user?.uid
            }
            .assign(to: \.userId, on: self)
            .store(in: &cancellables)
        
        authenticationService.$user
            .receive(on: DispatchQueue.main)
            .sink { [weak self] _ in
                self?.get()
            }
            .store(in: &cancellables)
    }
    
    
     
    
    func get( ) {
        store.collection(friendPath).document(userId).getDocument {(document, error) in
            let result = Result {
              try document?.data(as: Friends.self)
            }
            switch result {
            case .success(let f):
                if let f = f {
                    print("friends: \(f.myFriends)")
                    self.friendIDs = f.myFriends
                } else {
                    print("Document does not exist")
                }
            case .failure(let error):
                print("Error decoding city: \(error)")
            }
        }
    }

最后，在主内容视图中，我实例化一个这样的实例 -

@ObservedObject var friendRepository = FriendRepository()

那时我在控制台中看到以下输出

friends: ["PHyUe6mAc3LodM5guJJU"]
friends: ["PHyUe6mAc3LodM5guJJU"]

不知何故，我最终通过简单地实例化我的类的一个实例来调用 get() 函数两次，但我无法弄清楚这段代码是如何/为什么这样做的。

Answer 1

是的，我将两个属性设置为@Published，并且它们都在更改，因此它在代码中运行了两次。我不得不删除@published 标志之一。