antoinebelldev antoinebelldev - 3 years ago 148
JSON Question

Firebase Retrieve Data - Could not cast value

First, I have checked these answers that do not help me :
Swift JSON error, Could not cast value of type '__NSArrayM' (0x507b58) to 'NSDictionary' (0x507d74)

Get data from Firebase

When retrieving data from Firebase (3.x), I have an error that occurs which is :

Could not cast value of type '__NSArrayM' (0x10ca9fc30) to 'NSDictionary' (0x10caa0108).

with this code and tree :

Tree :

enter image description here

Retrieving function :

func retrievePlanes() {

print("Retrieve Planes")

ref = FIRDatabase.database().reference(withPath: "results")

ref.observe(.value, with: { snapshot in

var newItems: [Planes] = []

for item in snapshot.children {
let planesItem = Planes(snapshot: item as! FIRDataSnapshot)

self.planes = newItems



Planes.swift - To manage the data

import Foundation
import Firebase
import FirebaseDatabase

struct Planes {

let key: String!
let name: String!
let code:String!
let flightRange: Int?
let typicalSeats: Int?
let maxSeats: Int?
let wingSpan: String!
let takeoffLength: Int?
let rateClimb: Int?
let maxCruiseAltitude: Int?
let cruiseSpeed: String!
let landingLength: Int?
let engines: String!
let votes: Int?
let data: String!
let imagePlane:String!
let imageTakenFrom: String!
let ref: FIRDatabaseReference?

init(name: String, code: String, flightRange: Int, typicalSeats: Int, maxSeats: Int, wingSpan: String, takeoffLength: Int, rateClimb: Int, maxCruiseAltitude: Int, cruiseSpeed: String, landingLength: Int, engines: String, votes: Int, data: String, imagePlane: String, imageTakenFrom: String, key: String = "") {

self.key = key = name
self.code = code
self.flightRange = flightRange
self.typicalSeats = typicalSeats
self.maxSeats = maxSeats
self.wingSpan = wingSpan
self.takeoffLength = takeoffLength
self.rateClimb = rateClimb
self.maxCruiseAltitude = maxCruiseAltitude
self.cruiseSpeed = cruiseSpeed
self.landingLength = landingLength
self.engines = engines
self.votes = votes = data
self.imagePlane = imagePlane
self.imageTakenFrom = imageTakenFrom
self.ref = nil


init(snapshot: FIRDataSnapshot) {

ref = snapshot.ref
key = snapshot.key
let snapshotValue = snapshot.value as! [String:AnyObject]
name = snapshotValue["name"] as! String
code = snapshotValue["code"] as! String
flightRange = snapshotValue["intFlightRange"] as? Int
typicalSeats = snapshotValue["intTypicalSeats"] as? Int
maxSeats = snapshotValue["intMaxSeats"] as? Int
wingSpan = snapshotValue["wingSpan"] as! String
takeoffLength = snapshotValue["intTakeoffLength"] as? Int
rateClimb = snapshotValue["intRateClimb"] as? Int
maxCruiseAltitude = snapshotValue["intMaxCruiseAltitude"] as? Int
cruiseSpeed = snapshotValue["cruiseSpeed"] as! String
landingLength = snapshotValue["intLandingLength"] as? Int
engines = snapshotValue["engines"] as! String
votes = snapshotValue["votes"] as? Int
data = snapshotValue["data"] as! String
imagePlane = snapshotValue["planeImage"] as! String
imageTakenFrom = snapshotValue["imageTakenFrom"] as! String

on the line :
let snapshotValue = snapshot.value as! [String:AnyObject]

I suppose that is due to the snapshot value that can't be retrieved under
because of the
(It is working when I only have
in another case).

I also know that Firebase "converts" the JSON tree to these objects [link]:

  • NSString

  • NSNumber

  • NSArray

  • NSDictionnary

but I can't figure out what has to be changed in the snapshot.value line to make it work.

Thanks for your help.

EDIT : I just sent a troubleshooting request. Will post updates.
EDIT 2: See Jay's answer. In my case the tree was wrong.

Jay Jay
Answer Source

I took your code and shrunk it down a bit for testing, and it's working. (note Firebase 2.x on OS X and Swift 3 but the code is similar)

Firebase structure:

  "what-am" : {
    "results" : [ {
      "code" : "738/B738",
      "data" : "Boeing",
      "engines" : "Rolls"
    }, {
      "code" : "727/B727",
      "data" : "Boeing",
      "engines" : "Pratt"
    } ]

Here's the Planes struct

struct Planes {

    var code:String!
    var data: String!
    var engines: String!

    init(code: String, data: String, engines: String ) {

        self.code = code = data
        self.engines = engines

    init(snapshot: FDataSnapshot) {

        let snapshotValue = snapshot.value as! [String:AnyObject]

        code = snapshotValue["code"] as! String
        data = snapshotValue["data"] as! String
        engines = snapshotValue["engines"] as! String

and then the code that reads in two planes, populates and array and then prints the array.

let ref = self.myRootRef.child(byAppendingPath: "what-am/results")!

ref.observe(.value, with: { snapshot in

        if ( snapshot!.value is NSNull ) {
            print("not found")
        } else {

            var newItems: [Planes] = []

            for item in (snapshot?.children)! {
                let planesItem = Planes(snapshot: item as! FDataSnapshot)

            self.planes = newItems


and finally the output

[Swift_Firebase_Test.Planes(code: 738/B738, data: Boeing, engines: Rolls),
 Swift_Firebase_Test.Planes(code: 727/B727, data: Boeing, engines: Pratt)]

Key and name are nil as I removed then from the Planes structure.

The line you asked about

let snapshotValue = snapshot.value as! [String:AnyObject]

is valid as the snapshot contains a series of key:value pairs so String:AnyObject works.

This line changed due to Swift 3

for item in (snapshot?.children)!

but other than that, the code works.

Try this to ensure you are reading the correct node. This reads the above structure and prints out each engine type. (tested and works)

 let ref = self.myRootRef.child(byAppendingPath: "what-am/results")!
 ref.observe(.value, with: { snapshot in
      if ( snapshot!.value is NSNull ) {
           print("not found")
      } else {
           for child in (snapshot?.children)! {
                let snap = child as! FDataSnapshot
                let dict = snap.value as! [String: String]
                let engines = dict["engines"]
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