我无法从Firebase数据库读取数据

Question

我尝试在启动应用程序时填充表格视图，但是该方法不起作用。

var items = [ItemViewController.Item]()
override func viewDidLoad() { 
    super.viewDidLoad()

    Database.database().reference(withPath: "items").observe(.childAdded, with: { snapshot in
        var newItems: [ItemViewController.Item] = []
        for child in snapshot.children { // children of "items"
            if let snapshot = child as? DataSnapshot,

                let item = ItemViewController.Item(snapshot: snapshot) {
                newItems.append(item)
            }
        }
        self.items = newItems
        print(self.items)
        self.tableView.reloadData()
    })

}

（我的结构的初始化器）

init?(snapshot: DataSnapshot) {
    guard let value = snapshot.value as? [String: AnyObject], let name = value["name"] as? String, let surname = value["surname"] as? String, let age = value["age"] as? Int else { return nil }

    self.name = name
    self.key = snapshot.key
    //print("snapshot.key = \(snapshot.key)")
    self.surname = surname
    self.age = age

}