How to retrieve data from Firestore as soon as SwiftUI view appears? - swift

Question

I have this class CurrentUser that manages the currently logged in user and pulls the data for that user from Firebase.
One of CurrentUser's attributes is userEventIDs. I also have a collection of Events documents. Each user has their own array of event IDs that correspond to the events within the Events collection in my Firestore database.
On the MyAccount view struct I have an onAppear method that queries the Events collection based on the currentUser's array of eventIds, returns those Events, and then sorts them to be either before or after today based on the date of the event.
Currently the eventIds load in the first time this view is opened, but the query from the events comes back blank twice and only after the view is switched to another one and back to the MyAccount view will the page populate with these events.
Is there something I can do to make the events load on the first time the view is opened?
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")
}
}
}
}
}
View
.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"]!
}

Answer 1

A couple of quick notes:
Most Firebase calls are asynchronous (check out this article to understand why), so your call to Auth.auth().currentUser is most likely going to return nil. Instead, you should register an AuthenticationStateListener. See this sample code to see how it's done.
Instead of instantiating an empty User instance, make currentUserInformation optional
Mapping data is much easier using Firestore's support for Codable. I've written extensively about this, but the gist of it is, you'll be able to map documents with a single line of code (instead of having to manually map every single field). The Firestore documentation actually has a nice code snippet that you can adopt:
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)")
}
}
Avoid force unwrapping (using the ! operator), use optional unwrapping (using the ? operator), and the nil-coalescing operator (??) instead