Question

我正在从Firebase数据库中检索对象，我需要将它们转换为自定义结构类对象

类别：

struct Request {
    var Address: String!
    var Position: Position!
    var RequestID: String!
    var Status: String!
}

从我的Firebase数据库获取快照的功能：

self.ref.child("requests").observe(.childAdded, with: { snapshot in

    //I need to cast this snapshot object to a new Request object here

    let dataChange = snapshot.value as? [String:AnyObject]

    print(dataChange)

})

我怎样才能完成这项工作？

Answer 1

有几件事。 Firebase没有对象 - 它是一个JSON结构。当你像这样得到snapshot.value时：

let dataChange = snapshot.value as? [String:AnyObject]

[String：AnyObject]将数据定义为Dictionary。

然后，您可以像这样访问dataChange中的键：值对

let address = dataChange["address"]

和

let position = dataChange["position"]

从那里你可以创建新对象并在闭包中填充它们（例如将它们添加到数组中）或者在对象中放入更多智能并传递字典并让对象填充自己。

以下是伪代码，但它提供了以下过程：

//create the object and populate it 'manually'
self.ref.child("requests").observe(.childAdded, with: { snapshot in

    let dataChange = snapshot.value as? [String:AnyObject]

    let aRequest = Request()
    aRequest.address = dataChange["address"]
    aRequest.position = dataChange["position"]
    self.requestArray.append(aRequest)
})

或

Class Request {

   var address = ""
   var position = ""

   func initWithDict(aDict: [String: AnyObject]) {
    self.address = aDict["address"]
    self.position = aDict["position"]
   }

}

//let the object populate itself.
self.ref.child("requests").observe(.childAdded, with: { snapshot in

    let dataChange = snapshot.value as? [String:AnyObject]
    let aRequest = Request(initWithDict: dataChange)
    self.requestArray.append(aRequest)
})

Answer 2

如果您的结构中包含很多字段，则更容易执行以下操作（Swift 4 +）：

struct Request: Decodable {
    var Address: String
    var RequestID: String
    var Status: String
}

self.ref.child("requests").observe(.childAdded, with: { snapshot in
    guard let data = try? JSONSerialization.data(withJSONObject: snapshot.value as Any, options: []) else { return }
    let yourStructObject = try? JSONDecoder().decode(Request.self, from: data)
}

将Firebase快照投射到Swift 3对象

2 个答案: