Convert observe .value to .childAdded in swift - ios

Question

Currently I'm having some problems with this bit of code that is loading data from firebase database into an array. Since this is inside of viewDidLoad I have to empty my array food = [] before loading the data into it, if I don't then it will duplicate all the objects and I will have double duplicates the second time it loads, triple the third time and etc... However this was not a good fix for multiple reasons so what I would like is that it would only add new objects from the database with .childAdded however if I just switch out .value with .childAdded it will crash, I get a Thread 1: signal SIGABRT on this line: let dict = user_snap.value as! [String: String?]. I am pretty new to swift and don't know how to fix this, would really appreciate some help.
let parentRef = Database.database().reference().child("Recipes")
let storage = Storage.storage()
parentRef.observe(.value, with: { snapshot in
if ( snapshot.value is NSNull ) {
// DATA WAS NOT FOUND
print("– – – Data was not found – – –")
} else {
//Clears array so that it does not load duplicates
food = []
// DATA WAS FOUND
for user_child in (snapshot.children) {
let user_snap = user_child as! DataSnapshot
let dict = user_snap.value as! [String: String?]
//Defines variables for labels
let recipeName = dict["Name"] as? String
let recipeDescription = dict["Description"] as? String
let downloadURL = dict["Image"] as? String
let storageRef = storage.reference(forURL: downloadURL!)
storageRef.getData(maxSize: 1 * 1024 * 1024) { (data, error) -> Void in
let recipeImage = UIImage(data: data!)
food.append(Element(name: recipeName!, description: recipeDescription!, image: recipeImage!))
self.tableView.reloadData()
}
}
}
})

Answer 1

let dict = user_snap.value as! [String: String?]
Instead of
let dict = snapshot.value as! Dictionary<String, String>
and maybe you can do null test :
let dict = snapshot.value as! Dictionary<String, String>
if let recipeName = dict["Name"] as String!, let recipeDescription = dict["Description"] as String!, let downloadURL = dict["Image"] as String! {
let storageRef = storage.reference(forURL: downloadURL)
storageRef.getData(maxSize: 1 * 1024 * 1024) { (data, error) -> Void in
let recipeImage = UIImage(data: data!)
food.append(Element(name: recipeName, description: recipeDescription, image: recipeImage!, downloadURL: downloadURL))
self.tableView.reloadData()
}
}else {
print("Error! Could not decode data")
}

Answer 2

try this. It should work
for child in snapshot.children.allObjects as! [FIRDataSnapshot] {
let dict = child.value as! Dictionary<String, Any>
//.....
}