问题
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 :
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)
newItems.append(planesItem)
}
self.planes = newItems
self.tableView.reloadData()
})
}
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
self.name = 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
self.data = 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 [String:AnyObject] because of the Int below.
(It is working when I only have String in another case).
I also know that Firebase "converts" the JSON tree to these objects [link]:
NSStringNSNumberNSArrayNSDictionnary
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.
回答1:
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
self.data = 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)
newItems.append(planesItem)
}
self.planes = newItems
print(self.planes)
}
})
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"]
print(engines!)
}
}
})
回答2:
I think you are having an extra array in your results key-value on the firebase data.
You should try removing that array or
You may retrieve dictionary from first index of the array like;
// .. your code let snapshotValue = (snapshot.value as! [AnyObject])[0] as! [String:AnyObject]; // .. your code
回答3:
In your struct class make sure of these things:-
Avoid declaring your variables as
:Int?because that's practically nil, change them to:Int!Your key in your firebase is an Int and you are declaring your key in struct as
let key: String!, Change it tolet key: Int!Prefer your snapshot dictionary declaration as
let snapshotValue = snapshot.value as! [AnyHashable:Any](as per swift 3)
Then your init function to :-
Just change the line
let snapshotValue = snapshot.value as! [String:AnyObject]
To
let snapshotValue = (snapshot.value as! NSArray)[0] as! [String:AnyObject]
回答4:
update FIRDataSnapshot to DataSnapshot Swift 4
回答5:
Below is an example for Swift 4. Where you need to change FIRDataSnapshot to DataSnapshot
func fetchChats(chatId: String) {
ref.child("chats").child("SomeChildId").observe(.value) { (snapshot) in
for child in snapshot.children {
let data = child as! DataSnapshot //<--- Update this line
let dict = data.value as! [String: AnyObject]
let message = dict["message"]
print(message!)
}
}
}
来源：https://stackoverflow.com/questions/39934730/firebase-retrieve-data-could-not-cast-value