Question

好吧，我有一个函数，它必须找到等级的平均值，因此我将等级的总数和等级的总和存储在我的Firebase中（可以正常工作）。我正在尝试检索数据，但似乎它甚至都没有输入.observeSingleEvent的代码块。在尝试更新值时，我使用的是相同的方法，这意味着我得到了它们，并为其添加了新的评分然后使用下面的代码更新值：

let ratingObject = [
   "uid" : (user?.uid)! as String,
   "totalRatings" : newRating as Int,
   "amountOfRatings" : newAmountOfRating as int
   ] as [String : Any]

dbRef.setValue(ratingObject)

它没有给出错误，我只是迷路了

我尝试根据以下教程进行操作：https://www.youtube.com/watch?v=JV9Oqyle3iE

此线程中给出的答案：how parsing Firebase FDatasnapshot json data in swift只是使应用程序崩溃了

private func FindAverage(uid: String) -> Int {

    var totalRatings = 0
    var amountOfRatings = 1
    let dbRef = Database.database().reference().child("ratings").child(uid)

    dbRef.observeSingleEvent(of: .value, with: { snapshot in

        let dict = snapshot.value as? [String:Any]
        totalRatings = dict?["totalRatings"] as? Int ??  0
        amountOfRatings = dict?["amountOfRatings"] as? Int ??  1

    }){ (error) in
        print(error.localizedDescription)
    }

    return((Int)(totalRatings/amountOfRatings))
}

数据库结构

任何提示和帮助都非常感谢！

Answer 1

您正在尝试从完成处理程序中返回值。

您的功能应类似于：

private func findAverage(byUid uid: String, completion: @escaping (_ average: Int) -> Void) {
    // ...
    dbRef.observeSingleEvent(of: .value, with: { snapshot in
        guard let dict = snapshot.value as? [String: Any] else {
            return
        }
        totalRatings = dict["totalRatings"] as? Int ?? 0
        amountOfRatings = dict["amountOfRatings"] as? Int ?? 1

        completion((Int)(totalRatings / amountOfRatings))
    })
}

类似这样的内容，请检查Swift文档（有关完成处理程序等）。

Answer 2

尝试以下代码：

private func FindAverage(uid: String) -> Int {
  var totalRatings = 0
  var amountOfRatings = 1
  let dbRef = Database.database().reference().child("ratings").child(uid)
  dbRef.observeSingleEvent(of: .value, with: { snapshot in
     if snapshot.exists() {
        guard let dict = snapshot.value as? [String: Any] else {
           return
        }
        totalRatings = dict?["totalRatings"] as? Int ??  0
        amountOfRatings = dict?["amountOfRatings"] as? Int ??  1
     }
   }){ (error) in
      print(error.localizedDescription)
   }
   return((Int)(totalRatings/amountOfRatings))
}

尝试从Firebase Swift获取数据

2 个答案: