问题描述

我正在从 Firebase Google 检索数据.我正在检查我收到的数据是否过期.

I'm retrieving data from Firebase Google. I'm checking the data i received is expire or not.

func checkBought(movieName : String) -> Bool{

    var yesOrNo = false

    boughtRef.observeEventType(.Value, withBlock: { (snap) in

        if snap.value![movieName]! != nil {
            if self.timestamp > snap.value![movieName]! as! Double {
                //expire
                print("expire")
                yesOrNo = false
            } else {
                //not expire
                print("not expire")
                yesOrNo = true
            }
        } else {
            //not bought yet
            print("No movie")
            yesOrNo = false

        }
    })

    return yesOrNo
}

现在，return 语句在执行 firebase 代码之前返回并更改 yesOrNo 的值.

Now, the return statement is returning before the firebase code is executed and change the value of yesOrNo.

推荐答案

经典之作:

您不能从包含异步任务的方法返回任何内容

你需要一个完成块，很简单

You need a completion block, simply

func checkBought(movieName : String, completion:(Bool) -> Void) {

    boughtRef.observeEventType(.Value, withBlock: { (snap) in

    if snap.value![movieName]! != nil {
      if self.timestamp > snap.value![movieName]! as! Double {
        //expire
        print("expire")
        completion(false)
      } else {
        //not expire
        print("not expire")
        completion(true)
      }
    } else {
      //not bought yet
      print("No movie")
      completion(false)

    }
  })
}

或者更简单

func checkBought(movieName : String, completion:(Bool) -> Void) {
  boughtRef.observeEventType(.Value, withBlock: { (snap) in
    if let movieStamp = snap.value![movieName] as? Double where self.timestamp <= movieStamp {
      //not expire
      print("not expire")
      completion(true)
    } else {
      // expire or not bought yet
      print("expire or no movie")
      completion(false)
    }
  })
}

并用

checkBought("Foo") { flag in
   print(flag)
}

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