How to make firebase .observeSingleEventOf function run synchronously - ios

I am running Firebase's .getSingleEventOf function to read data from my database in my program, and it is an asynchronous function. How would I make it synchronous (or make another synchronous function to house the code)?
I've tried to use the data passed through the function, but it hasn't been working! It only returns 0 elements, even though I know that I have data with the specific letters in my database.
import Foundation
import Firebase
struct CompeteUserFinderService {
static func findCompetitors(contains letters: String?) -> [String] {
//Make sure there was an input
guard let letters = letters else { return [] }
var usernames = [String]()
//Database reference
let ref = Database.database().reference().child("usernames")
ref.observeSingleEvent(of: .value) { (snapshot) in
//Creates an array of all values in the usernames branch
let value = Array((snapshot.value as! [String: Any]).keys)
usernames = value.map { $0.lowercased() }.filter { $0.contains(letters.lowercased()) }
}
return usernames
}
}

Related

SwiftUI: How to iterate over Documents in Cloud Firestore Collection and get Data?

I have this small project where a user can post an Image together with a quote, I would then like to display the Image and the quote togehter in their profile, as well as somewhere else so other users can see the post.
If I have this Cloud Firestore setup
where all of the Image Docs have the same 3 fields, but with different values.
How can I then iterate over all of the Image Docs and get the the Url and the quote? So I later can display the url together with the correct Quote?
And if this is for some reason not possible, is it then possible to get the number of Documents in a Collection?
BTW, I am not very experienced so I would appreciate a "kid friendly" answer if possible
Firestore
.firestore()
.collection("Images")
.getDocuments { (snapshot, error) in
guard let snapshot = snapshot, error == nil else {
//handle error
return
}
print("Number of documents: \(snapshot.documents.count ?? -1)")
snapshot.documents.forEach({ (documentSnapshot) in
let documentData = documentSnapshot.data()
let quote = documentData["Quote"] as? String
let url = documentData["Url"] as? String
print("Quote: \(quote ?? "(unknown)")")
print("Url: \(url ?? "(unknown)")")
})
}
You can get all of the documents in a collection by calling getDocuments.
Inside that, snapshot will be an optional -- it'll return data if the query succeeds. You can see I upwrap snapshot and check for error in the guard statement.
Once you have the snapshot, you can iterate over the documents with documents.forEach. On each document, calling data() will get you a Dictionary of type [String:Any].
Then, you can ask for keys from the dictionary and try casting them to String.
You can wee that right now, I'm printing all the data to the console.
Keep in mind that getDocuments is an asynchronous function. That means that it runs and then returns at an unspecified time in the future. This means you can just return values out of this function and expect them to be available right after the calls. Instead, you'll have to rely on things like setting properties and maybe using callback functions or Combine to tell other parts of your program that this data has been received.
If this were in SwiftUI, you might do this by having a view model and then displaying the data that is fetched:
struct ImageModel {
var id = UUID()
var quote : String
var url: String
}
class ViewModel {
#Published var images : [ImageModel] = []
func fetchData() {
Firestore
.firestore()
.collection("Images")
.getDocuments { (snapshot, error) in
guard let snapshot = snapshot, error == nil else {
//handle error
return
}
print("Number of documents: \(snapshot.documents.count ?? -1)")
self.images = snapshot.documents.compactMap { documentSnapshot -> ImageModel? in
let documentData = documentSnapshot.data()
if let quote = documentData["Quote"] as? String, let url = documentData["Url"] as? String {
return ImageModel(quote: quote, url: url)
} else {
return nil
}
}
}
}
}
struct ContentView {
#ObservedObject var viewModel = ViewModel()
var body : some View {
VStack {
ForEach(viewModel.images, id: \.id) { item in
Text("URL: \(item.url)")
Text("Quote: \(item.quote)")
}
}.onAppear { viewModel.fetchData() }
}
}
Note: there are now fancier ways to get objects decoded out of Firestore using FirebaseFirestoreSwift and Combine, but that's a little outside the scope of this answer, which shows the basics

the retrieved data doesn't append in my array swift4

I'm trying to append "the retrieved data -Keys- from firebase" into an array but it doesn't work
This is the for loop output #2 the retrieved keys
This the keys from firebase
This is the code
let ref = Database.database().reference()
ref.child("Faculty ").observe(.value, with: { (snapshot) in
if let result = snapshot.children.allObjects as? [DataSnapshot] {
for child in result {
let FacultyName = child.key as! String
print(FacultyName)
self.NamesofFac.append(FacultyName)
}
}
})
for i in 0...self.NamesofFac.count {
print(self.NamesofFac.count)
print(" line")
print(self.NamesofFac)
The problem you are having is the Firebase Observe function give a callback in the form of a (snapshot).
It takes a bit of time to go to the web to get the data, therefore, firebase returns the data asynchronously. Therefore your code in your for loop will run before your firebase data has been returned. At the time your for loop code runs the array is still blank. But the for loop code in a separate function as you see in my sample code and call it straight after your for loop inside your firebase observe call.
Try this instead:
override func viewDidLoad() {
getFirebaseData()
}
func getFirebaseData() {
let ref = Database.database().reference()
ref.child("Faculty ").observe(.value, with: { (snapshot) in
if let result = snapshot.children.allObjects as? [DataSnapshot] {
for child in result {
let FacultyName = child.key as! String
print(FacultyName)
self.NamesofFac.append(FacultyName)
}
printNames()
}
})
}
func printNames() {
for i in 0...self.NamesofFac.count {
print(self.NamesofFac.count)
print(" line")
print(self.NamesofFac)
}
}
This was it won't print the names until they have been fully loaded from firebase.
PS: Your naming conventions are incorrect. You seem to be naming variables with a capital letter. Variables should be camel case. Classes should start with a capital.

Cannot retrieve data from Firebase using Swift

As the title says I have a weird problem to retrieve simple data from Firebase, but I really can't figure out where I'd go wrong.
This is my schema:
And this the code:
import Firebase
let DB_BASE = Database.database().reference()
class FirebaseService {
static let instance = FirebaseService()
private var REF_BASE = DB_BASE
private var REF_SERVICE_STATUS = DB_BASE.child("Service_Status")
struct ServiceStatus {
var downloadStatus: Bool
var uploadStatus: Bool
}
func getServiceStatus() -> (ServiceStatus?) {
var serviceStatus: ServiceStatus?
REF_SERVICE_STATUS.observeSingleEvent(of: .value) { (requestSnapshot) in
if let unwrapped = requestSnapshot.children.allObjects as? [DataSnapshot] {
for status in unwrapped {
serviceStatus.downloadStatus = status.childSnapshot(forPath: "Download_Status").value as! Bool
serviceStatus.uploadStatus = status.childSnapshot(forPath: "Upload_Status").value as! Bool
}
// THANKS TO JAY FOR CORRECTION
return sponsorStatus
}
}
}
}
but at the end serviceStatus is nil. Any advice?
I think you may be able to simplify your code a bit to make it more manageable. Try this
let ssRef = DB_BASE.child("Service_Status")
ssRef.observeSingleEvent(of: .value) { snapshot in
let dict = snapshot.value as! [String: Any]
let down = dict["Download_Status"] ?? false
let up = dict["Upload_Status"] ?? false
}
the ?? will give the down and up vars a default value of false if the nodes are nil (i.e. don't exist)
Oh - and trying to return data from a Firebase asynchronous call (closure) isn't really going to work (as is).
Remember that normal functions propagate through code synchronously and then return a value to the calling function and that calling function then proceeds to the next line of code.
As soon as you call your Firebase function, your code is going to happily move on to the next line before Firebase has a chance to get the data from the server and populate the return var. In other words - don't do it.
There are always alternatives so check this link out
Run code only after asynchronous function finishes executing

Trying to create an array within an array dynamically with a GET Request

I'm trying to create an array within an array with a GET Request I'm making. I want the data look something like
[heroesOfLOTR[Gandalf, Frodo, Aragorn], heroesOfStarWars[Yoda, Luke, ObiWan],heroesOfWheelOfTime[Rand, Matt, Perrin]]
I've looked through multiple posts about multi-dimensional arrays, but the data is usually with a set number, and does not work dynamically. I also see a lot of results that look like this:
[[1,2,3][1,2,3,4][1,2]]
Currently, thats what my data looks like, and can't figure to a solution to get it to work like the first array mentioned.
I've tried at least 10 or 15 combinations of code, but am unable to find a solution.
JSON
{ HeroLOTR heroes:[ {Sam} {Frodo} {Gandalf}], {HeroesOfStarWars heroes:[ {Yoda} {Luke} {ObiWan}]
There are a few things I'd recommend here:
First, create a more descriptive class or struct for your heroes. This isn't a requirement but will make your code much more readable and understandable as you continue development.
class Hero { // Switch "class" to "struct" if you want a struct
// Add whatever properties you want here
let name: String
init?(json: [String: Any]) {
guard let name = json["name"] as? String else {
return nil
}
self.name = name
}
}
Second, it appears you're trying to put each of the heroes into an array (a set would work here too). You can again create a class or struct to hold these heroes.
class HeroGroup { // Just switch "class" to "struct" if you want a struct
let name: String
let heroes: [Hero]
init?(json: [String: Any?]) {
guard let name = json["name"] as? String else {
return nil
}
self.name = name
self.heroes = (json["heroes"] as? [[String: Any]])?.flatMap { Hero(json: $0) } ?? []
}
}
Lastly, when you receive your response, you can just write code like the following in your completion closure:
guard let groups = response.value.arrayValue as? [[String: Any]] else {
return // Have JSON that you can't parse
}
// This will give you [HeroGroup]
self.groupsOfHeroes = groups.flatMap { HeroGroup(json: $0) } // This is a property on your view controller
tableView.reloadData()

Array of struct not updating outside the closure

I have an array of struct called displayStruct
struct displayStruct{
let price : String!
let Description : String!
}
I am reading data from firebase and add it to my array of struct called myPost which is initialize below
var myPost:[displayStruct] = []
I made a function to add the data from the database to my array of struct like this
func addDataToPostArray(){
let databaseRef = Database.database().reference()
databaseRef.child("Post").queryOrderedByKey().observe(.childAdded, with: {
snapshot in
let snapshotValue = snapshot.value as? NSDictionary
let price = snapshotValue?["price"] as! String
let description = snapshotValue?["Description"] as! String
// print(description)
// print(price)
let postArr = displayStruct(price: price, Description: description)
self.myPost.append(postArr)
//if i print self.myPost.count i get the correct length
})
}
within this closure if I print myPost.count i get the correct length but outside this function if i print the length i get zero even thou i declare the array globally(I think)
I called this method inside viewDidLoad method
override func viewDidLoad() {
// setup after loading the view.
super.viewDidLoad()
addDataToPostArray()
print(myPeople.count) --> returns 0 for some reason
}
I want to use that length is my method below a fucntion of tableView
public func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return myPost.count --> returns 0
}
Any help would be greatly appreciated!
You making a asynchronous network request inside closure and compiler doesn't wait for the response, so just Reload Table when get post data. replace the code with below it work works fine for you. All the best.
func addDataToPostArray(){
let databaseRef = Database.database().reference()
databaseRef.child("Post").queryOrderedByKey().observe(.childAdded, with: {
snapshot in
let snapshotValue = snapshot.value as? NSDictionary
let price = snapshotValue?["price"] as! String
let description = snapshotValue?["Description"] as! String
// print(description)
// print(price)
let postArr = displayStruct(price: price, Description: description)
self.myPost.append(postArr)
print(self.myPost.count)
print(self.myPost)
self.tableView.reloadData()
//if i print self.myPost.count i get the correct length
})
}
Firebase observe call to the database is asynchronous which means when you are requesting for the value it might not be available as it might be in process of fetching it.
That's why your both of the queries to count returns 0 in viewDidLoad and DataSource delegeate method.
databaseRef.child("Post").queryOrderedByKey().observe(.childAdded, with: { // inside closure }
Inside the closure, the code has been already executed and so you have the values.
What you need to do is you need to reload your Datasource in main thread inside the closure.
databaseRef.child("Post").queryOrderedByKey().observe(.childAdded, with: {
// After adding to array
DispatchQueue.main.asyc {
self.tableView.reloadData()
}
}

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