我使用的是 Firebase，直到最近我才可以按字母顺序获取数据。我从不使用查询，我总是只使用数据快照并逐一对它们进行排序。最近，snapVal 中的数据并不总是按字母顺序排列。我该怎么做才能获得按字母顺序排序的 snapVal 数据，就像它在数据库的快照中一样？

真实示例:有 4 条消息，id1-id4(按此顺序)。它们包含消息“1”-“4”。快照看起来正确。但是 snapVal (snapshot.value) 看起来像这样:

["id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}, "id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}]

快照的样子:

["id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}]

为了获得 snapVal，我使用了这个:

if let snapVal = snapshot.value as? [String: AnyObject] {
     // Comes out of order..
}

澄清一下:

快照(结果正确):

Snap (CHAT) {
    id1 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 1;
        TIME = "8:12 PM";
    };
    id2 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 2;
        TIME = "8:12 PM";
    };
    id3 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 3;
        TIME = "8:12 PM";
    };
    id4 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 4;
        TIME = "8:12 PM";
    };
}

这是 print(snapVal.keys) 的输出 if let snapVal = snapshot.value as? [字符串:AnyObject]:

LazyMapCollection<Dictionary<String, AnyObject>, String>(_base: ["id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}, "id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}], _transform: (Function))

我的代码:

  self.firebase.child("Chats").child(chatID).queryOrderedByKey().observeSingleEvent(of: .value, with: { (snapshot) in
                          print(snapshot)
                        if let snapVal = snapshot.value as? [String: AnyObject] {

                            print(snapVal)

                            for c in snapVal {
                                print("checking Message as child")
                                let message = c.value["MESSAGE"] as? String

                                let fn = c.value["FIRST_NAME"] as? String
                                let ln = c.value["LAST_NAME"] as? String

                                let USER_ID = c.value["ID"] as? String

                                if let userID = USER_ID {
                                    if let msg = message {
                                        if let firstName = fn {
                                            if let lastName = ln {
                                                let username = "\(firstName) \(lastName)"
                                                self.addMessage(userID, text: msg, name: username)

                                                print("Message added! \nMessage Info:")
                                                print("User ID: \(userID)")
                                                print("text: \(msg)")
                                                print("Username: \(username)")
                                            } else {
                                                print("LN did not pass")
                                            }
                                        } else {
                                            print("FN did not pass")
                                        }
                                    } else {
                                        print("Msg did not pass")
                                    }
                                } else {
                                    print("User ID did not pass")
                                }
                            }
                          }  
})

最佳答案

由于您没有共享必要的代码，我假设您正在按照以下方式做一些事情:

ref!.queryOrdered(byChild: "text").observe(.value, with: { (snapshot) in
    print("\(snapshot.value)")
})

当您对 Firebase 位置执行查询时，系统会根据查询返回包含有关项目顺序信息的数据。当您观察到 value 事件时，快照包含键、值和子项的顺序。

但是当您转换请求snapshot.value 属性时，所有信息都必须转换成字典。每个子项的键和值在这种转换中幸存下来，但有关排序的信息丢失了。

因此，您必须使用快照的 children 属性以正确的顺序遍历子项:

ref!.queryOrdered(byChild: "text").observe(.value, with: { snapshot in
    for child in snapshot.children {
        print("child \(child)")
    }
})

关于swift - Firebase 按顺序获取数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40166483/