Getting Value From FirebaseDB - ios

Question

I am trying to get values from my firebasedb, on run, ref.observeSingleEvent(of: .value, with: { snapshot in causes fatal error unexpectedly found nil while unwrapping an Optional value. As im sure you can tell... I have no idea what im doing... Thank you in advance...
func geths() -> Int{
var sch:Int = 0
var nam:String = ""
print("start geths")
ref.observeSingleEvent(of: .value, with: { snapshot in
if (snapshot.exists()){
print("snapexist")
if let snapval = snapshot.value as? [String:AnyObject]{
let hs = snapval["hs"] as? String
let name = snapval["name"] as? String
self.hso = hs!
self.nameo = name!
nam = self.nameo
if let myNumber = NumberFormatter().number(from: self.hso) {
let i = myNumber.intValue
sch = i
}else{
sch = 0
}
}else{
print("error")
}
}else{
print("error")
}
})
return sch
}
EDIT************
still dont work :( same errors
func geths() -> Int{
var sch:Int = 0
var nam:String = ""
print("start geths")
ref.observeSingleEvent(of: .value, with: { (snapshot) in
if (snapshot.exists()){
print("snapexist")
let snapval = snapshot.value as? NSDictionary
let hs = snapval?["hs"] as? String ?? ""
let name = snapval?["name"] as? String ?? ""
if (hs != nil){
self.hso = hs
}else{
self.hso = "0"
}
if (name != nil){
self.nameo = name
}else{
self.nameo = "bob"
}
nam = self.nameo
if let myNumber = NumberFormatter().number(from: self.hso) {
let i = myNumber.intValue
sch = i
}else{
sch = 0
}
}else{
print("error")
}
})
return sch
}

Answer 1

create firebase reference like this :
var ref: FIRDatabaseReference!
ref = FIRDatabase.database().reference()
for more details go though this link :
https://firebase.google.com/docs/database/ios/read-and-write

Answer 2

You must initialize the ref variable, you was only declare it by
var ref: FIRDatabaseReference!
For example
var ref: FIRDatabaseReference! = FIRDatabase.database().reference(withPath: "hs")
You may read example about using Firebase here:
https://www.raywenderlich.com/139322/firebase-tutorial-getting-started-2