Firebase 检索数据 - 无法转换值

Question

首先，我检查了这些对我没有帮助的答案： Swift JSON error, Could not cast value of type '__NSArrayM' (0x507b58) to 'NSDictionary' (0x507d74)

Get data from Firebase

从 Firebase (3.x) 检索数据时，出现以下错误：

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

使用此代码和树：

树：

检索函数：

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 - 管理数据

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
    }

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

我想这是由于下面的Int 导致无法在[String:AnyObject] 下检索快照值。 （在另一种情况下，当我只有 String 时它正在工作）。

我也知道 Firebase 将 JSON 树“转换”为这些对象[link]：

• NSString
• NSNumber
• NSArray
• NSDictionnary

但我不知道要在 snapshot.value 行中更改什么才能使其正常工作。

感谢您的帮助。

编辑：我刚刚发送了故障排除请求。将发布更新。 编辑 2：请参阅 Jay 的回答。就我而言，树是错误的。

Answer 1

我把你的代码缩小了一点进行测试，它正在工作。 （注意 OS X 和 Swift 3 上的 Firebase 2.x，但代码相似）

Firebase 结构：

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

这是平面结构

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
    }
}

然后代码在两个平面中读取，填充和数组，然后打印数组。

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)

        }
})

最后是输出

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

当我从 Planes 结构中删除时，键和名称为零。

你问的那行

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

有效，因为快照包含一系列键：值对，因此 String:AnyObject 有效。

由于 Swift 3，这一行发生了变化

for item in (snapshot?.children)!

但除此之外，代码可以工作。

试试这个以确保您正在读取正确的节点。这将读取上述结构并打印出每个引擎类型。 （经过测试和工作）

 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!)
           }    
      }
 })

Answer 2

我认为您在 firebase 数据的结果键值中有一个额外的数组。

• 您应该尝试删除该数组或

• 您可以从数组的第一个索引中检索字典，例如；

  // .. your code
  let snapshotValue = (snapshot.value as! [AnyObject])[0] as! [String:AnyObject];
  // .. your code
  

Answer 3

在你的结构类中确保这些事情：-

• 避免将变量声明为 :Int?，因为这实际上是 nil，请将它们更改为 :Int!

• 您在 Firebase 中的密钥是一个 Int，并且您将 struct 中的密钥声明为 let key: String!，将其更改为 let key: Int!

• 首选您的快照字典声明为 let snapshotValue = snapshot.value as! [AnyHashable:Any]（根据 swift 3）

然后你的初始化函数：-

换行就行了

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

到

let snapshotValue = (snapshot.value as! NSArray)[0] as! [String:AnyObject]

Answer 4

将 FIRDataSnapshot 更新为 DataSnapshot Swift 4

Answer 5

以下是 Swift 4 的示例。您需要将 FIRDataSnapshot 更改为 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!)
        }
    }
}