swift 4 : Parsing Firebase 4 snapshot to Model

Question

我使用的是 Swift 4 和 Firebase 4

我有一个名为 Part 的模型

class Part {
    var db_id: String?
    var can_8130: Bool?
    var description: String?
    var has_amm: Bool?
    var is_esd: Bool?
    var is_hazmat: Bool?
    var is_priority: Bool?
    var msn: String?
    var partNum: String?
    var received: String?
    var receiver: String?
    var tail: String?

    init(db_id:String?, can_8130: Bool, description: String?, has_amm: Bool?, is_esd: Bool?, is_hazmat: Bool?, is_priority: Bool?, msn: String?, partNum: String?, received: String?, receiver: String?, tail: String?) {
        self.db_id = db_id;
        self.can_8130 = can_8130;
        self.description = description;
        self.has_amm = has_amm;
        self.is_esd = is_esd;
        self.is_hazmat = is_hazmat;
        self.is_priority = is_priority;
        self.msn = msn;
        self.partNum = partNum;
        self.received = received;
        self.receiver = receiver;
        self.tail = tail;
    }
}

在我的 ViewController 中，我有 UITableViewDataSource

@IBOutlet weak var tableView: UITableView!

var partsArray: [Part] = []

在 ViewDidLoad 中，我调用retrieveParts()(来自 Firebase4 实时数据库)

function retrieveParts() {
    let rampPartsDB = Database.database().reference().child("ramp-parts")
    rampPartsDB.observe(.childAdded) { (snapshot) in
        if snapshot.childrenCount > 0 {
            //print(snapshot)
            if let snapValue = snapshot.value as? [String:Any] {
                print(snapValue)
                let dbID = snapValue["db_id"] as! String
                let can8130 = snapValue["can_8130"] as! Bool
                let description = snapValue["description"] as! String
                let hasAMM = snapValue["has_amm"] as! Bool
                let isESD = snapValue["is_esd"] as! Bool
                let isHazmat = snapValue["is_hazmat"] as! Bool
                let isPriority = snapValue["is_priority"] as! Bool
                let msn = snapValue["msn"] as! String
                let partNum = snapValue["partNum"] as! String
                let received = snapValue["received"] as! String
                let receiver = snapValue["receiver"] as! String
                let tail = snapValue["tail"] as! String

                var item = Part(db_id: dbID, can_8130: can8130, description: description, has_amm: hasAMM, is_esd: isESD, is_hazmat: isHazmat, is_priority: isPriority, msn: msn, partNum: partNum, received: received, receiver: receiver, tail: tail)
                print("ITEM: \(item)" )
                self.partsArray.append(item)
            }
        } // end if
    } // end observe()
} // end retrievePart()

现在，“打印零件阵列”显示 []

和

语句 print(snapValue) 和 print("ITEM: (item)") 为每个成员生成:

["tail": N117UA, "is_priority": 0, "received": 2018-02-22T09:12:07S, "can_8130": 1, "description": PARTS ON A PLANE, "is_hazmat": 0, "is_esd": 1, "has_amm": 0, "partNum": b51-09-1035, "msn": , "receiver": Jon Gravois, "db_id": 99990] ITEM: Aero_Eco.Part

非常感谢任何帮助!

Answer 1

你的快照值是字典里面只需输入此代码if let snapValue = snapshot.value as? [String:Any]' 并在其中 print snapValue 你可以看到所有键值在那里。从中通过键获取每个值并创建模型并附加到您的 partsArray`

在深入了解 Firebase 之前，您需要了解几件事。

Firebase 是一个基于 JSON(键 - 值)的实时数据库类型，允许多个观察者对任意键进行观察。

其中可以有以下事件类型

typedef NS_ENUM(NSInteger, FIRDataEventType) {
    /// A new child node is added to a location.
    FIRDataEventTypeChildAdded,
    /// A child node is removed from a location.
    FIRDataEventTypeChildRemoved,
    /// A child node at a location changes.
    FIRDataEventTypeChildChanged,
    /// A child node moves relative to the other child nodes at a location.
    FIRDataEventTypeChildMoved,
    /// Any data changes at a location or, recursively, at any child node.
    FIRDataEventTypeValue
} NS_SWIFT_NAME(DataEventType);

但是还有一件事更重要的是 observeSingleEventOfType 和 observeEventType 我的建议是您只需查看文档 https://firebase.google.com/docs/database/ios/start

如果你观察singleEvent，当这条语句执行时它只会执行一次。如果您观察正常事件，每当您的任何子树发生变化时，它都会通知您。因此建议明智地使用它，不要将观察者放在树对象的顶部。

如果您只需要一次，您应该做什么。

观察按键上的单个事件，然后添加另一个观察者，即 childAdded