将Firebase快照投射到Swift 3对象

Question

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

类：

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

从我的Firebase数据库获取快照的函数：

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)

})

我该怎么做？

Answer 1

如果你的结构体有很多字段，这样做会更容易（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)
}

Answer 2

有几件事。Firebase没有对象-它是JSON结构。当您获得如下的snapshot.value时：

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

[String：AnyObject]将数据定义为字典。

然后，您可以像这样访问dataChange中的key：value对

let address = dataChange["address"]

和

let position = dataChange["position"]

从那里，您可以创建新对象并将其填充在闭包中（例如，将它们添加到数组中），也可以在对象中添加更多智能，然后传递字典并让对象自行填充。

以下是伪代码，但它介绍了该过程：

//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)
})

要么

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)
})