Swift service class to retrieve Firebase data - swift

Question

I have a service class to fetch data from my Firebase:
class Service {
var myName = String?
var myDev: String?
func getData() {
let databaseRef = FIRDatabase.database().reference()
databaseRef.child("Data").observeSingleEvent(of: .value, with: { (snapshot) in
let value = snapshot.value as? NSDictionary
let name = value?["name"] as? String ?? ""
self.myName = name
let dev = value?["dev"] as? String ?? ""
self.myDev = dev
}) { (error) in
print(error.localizedDescription)
}
}
}
and realization in my Main class:
var service = Service()
override func viewDidLoad(){
super.viewDidLoad()
service.getData()
configureLabel()
}
private func configureLabel(){
self.titleLabel.text = service.myName
self.devLabel.text = service.myDev
}
The problem is: data from Firebase fetched only after my label got values of myName and myDev.Thus, this values is nil.

Answer 1

this is not the best solution, but it should solve your problem.
struct MyStructure {
var name = ""
var dev = ""
init(with dictionary: [String: String]) {
if let name = dictionary["name"] {
self.name = name
}
if let dev = dictionary["dev"] {
self.dev = dev
}
}
}
class Service {
let databaseRef = FIRDatabase.database().reference()
func getData(completion: #escaping ((_ structure: MyStructure) -> Void)) {
databaseRef.child("Data").observeSingleEvent(of: .value, with: { snapshot in
if let value = snapshot.value as? [String: String] {
completion(MyStructure(with: value))
}
}) { (error) in
print(error.localizedDescription)
}
}
}
let service = Service()
override func viewDidLoad() {
super.viewDidLoad()
service.getData { myStructure in
DispatchQueue.main.async {
self.titleLabel.text = myStructure.name
self.devLabel.text = myStructure.dev
}
}
}

Answer 2

Of course it does. The getData() method makes an asynchronous call to the Firebase service. Meaning, the .observeSingleEvent method of firebase runs in a async queue as most code blocks that makes a service call. So the compiler reaches to getData() line, pushes the block to a different queue and continues to compile the next lines which are in the original queue. If you want those lines to run after you receive the response, you may add a closure to your getData() method as a parameter.
You can do something like this:
getData(completion: () -> Void) {
let databaseRef = FIRDatabase.database().reference()
databaseRef.child("Data").observeSingleEvent(of: .value, with: { (snapshot) in
let value = snapshot.value as? NSDictionary
let name = value?["name"] as? String ?? ""
self.myName = name
let dev = value?["dev"] as? String ?? ""
self.myDev = dev
completion()
}) { (error) in
print(error.localizedDescription)
}
}
override func viewDidLoad(){
super.viewDidLoad()
service.getData(completion: { Void in
configureLabel()
})
}