如何从Firestore检索数据，只要SwiftUI视图出现?

我有这个类CurrentUser，它管理当前登录的用户并从Firebase提取该用户的数据。

CurrentUser的属性之一是userEventIDs。我还收集了一些Events文档。每个用户都有自己的事件id数组，这些事件id对应于我的Firestore数据库中Events集合中的事件。

在MyAccount视图结构上，我有一个onAppear方法，该方法根据currentUser的eventIds数组查询Events集合，返回这些事件，然后根据事件的日期将它们排序为今天之前或之后。

当前eventIds在第一次打开这个视图时加载，但是事件的查询两次返回空白，只有在视图切换到另一个并返回到MyAccount视图后，页面才会填充这些事件。

是否有一些我可以做的事情，使事件加载在第一次打开的视图?

CurrentUser

class CurrentUser: ObservableObject {
let user = Auth.auth().currentUser

@Published var currentUserInformation = User(id: "", name: "", email: "'", accountType: "", profPicURL: "", coverPhotoURL: "", numberFollowers: nil, description: nil, location: nil, websiteLink: nil, orgID: nil, userEventIDs: [String](), userEvents: [Event]())

init() {
getUserInformation()
}

func getUserInformation() {
let UID = user!.uid
let database = Firestore.firestore()
database.collection("Organizers").whereField("Organizer ID", isEqualTo: UID).getDocuments() { (querySnapshot, err) in

if err != nil {
print("Error getting documents: (err!)")
}

for document in querySnapshot!.documents {
self.currentUserInformation.id = document.documentID
self.currentUserInformation.name = document.get("Organization Name") as! String
self.currentUserInformation.email = document.get("Email") as! String
self.currentUserInformation.accountType = document.get("Account Type") as! String
self.currentUserInformation.profPicURL = document.get("Profile Pic URL") as! String
self.currentUserInformation.coverPhotoURL = document.get("Cover Pic URL") as! String
self.currentUserInformation.numberFollowers = (document.get("Number of Followers") as! Int)
self.currentUserInformation.description = (document.get("Organization Description") as! String)
self.currentUserInformation.websiteLink = (document.get("Organization Website Link") as! String)
self.currentUserInformation.location = (document.get("Organization Location") as! String)
self.currentUserInformation.orgID = (document.get("Organizer ID") as! String)
self.currentUserInformation.userEventIDs = (document.get("Events") as! [String])
self.currentUserInformation.accountType = "Organizer"
}
}

if self.currentUserInformation.id == "" {
database.collection("Activists").whereField("UID", isEqualTo: UID).getDocuments() { (querySnapshot, err) in

if err != nil {
print("Error getting documents: (err!)")
}

for document in querySnapshot!.documents {

self.currentUserInformation.id = document.documentID
let firstName = document.get("First Name") as! String
let lastName = document.get("Last Name") as! String
self.currentUserInformation.name = "(firstName) (lastName)"
self.currentUserInformation.email = document.get("Email") as! String
self.currentUserInformation.accountType = "Activist"
self.currentUserInformation.profPicURL = document.get("Profile Pic") as! String
self.currentUserInformation.userEventIDs = (document.get("Events") as! [String])

}
}
}
}

func getUserEvents() {
let database = Firestore.firestore()
let eventRef = database.collection("Events")
for eventID in self.currentUserInformation.userEventIDs {
for event in self.currentUserInformation.userEvents {
if event.id == eventID {
break
}
}
eventRef.document(eventID).getDocument() { (document, error) in
if let document = document {
let id = document.documentID
let eventTitle = document.get("Name") as! String
let organizer = document.get("Organizer") as! String
let organizerID = document.get("Organizer ID") as! String
let eventDescription = document.get("Description") as! String
let date = document.get("Date") as! String
let time = document.get("Time") as! String
let location = document.get("Location") as! String
let numAttending = document.get("Number Attending") as! Int
let eventPhotoURL = document.get("Event Photo URL") as! String
self.currentUserInformation.userEvents.append(Event(id: id, eventTitle: eventTitle, eventOrganizer: organizer, eventOrganizerID: organizerID, eventDescription: eventDescription, date: date, time: time, location: location, numAttending: numAttending, eventPhotoURL: eventPhotoURL))
} else {
print("Document does not exist")
}
}
}
}
}

<<h3>视图/h3>

.onAppear() {
if currentActivist.currentUserInformation.userEvents.count != currentActivist.currentUserInformation.userEventIDs.count {
currentActivist.getUserEvents()
print("Getting user events")
}
pastEvents = MyAccountActivistView.getSortedEvent(actEvents: currentActivist.currentUserInformation.userEvents)["Past"]!
futureEvents = MyAccountActivistView.getSortedEvent(actEvents: currentActivist.currentUserInformation.userEvents)["Upcoming"]!
}

几点提示:

大多数Firebase调用都是异步的(请查看本文以了解原因)，因此对Auth.auth().currentUser的调用很可能返回nil。相反，您应该注册一个AuthenticationStateListener。看看这个示例代码，看看它是如何完成的。
将currentUserInformation设为可选，而不是实例化一个空的User实例

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)")
}
}

避免强制展开(使用!操作符)，使用可选的展开(使用?操作符)，而不是

CurrentUser

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