Swift Firebase函数返回

问题描述

我很难在返回函数中使用Firebase值.对我来说，这似乎是一个持续存在的问题.我已经写了一个基本的例子来说明我的问题.我该怎么做呢?

I'm having a hard time with Firebase values in return functions. This seems to be an ongoing problem for me. I have written up a basic example of my issue. How do I go about doing this?

func getChartIndexValues(completion:@escaping (Double) -> ()) {

    //Firebase Initialization
    var ref: FIRDatabaseReference!
    ref = FIRDatabase.database().reference()

    ref.child("general_room_index").observeSingleEvent(of: .value, with: {(snapshot) in

        let snapDict = snapshot.value as? NSDictionary
        var zero = snapDict?["0"] as! Double

        completion(zero)
        })

}


   returnFunction() -> (Double) {

      getChartIndexValues() { (zero) -> () in

            let testValue = zero
        }


     return //THis is my problem
}

推荐答案

您已经暗示了您的问题，但没有明确指出.问题是您不能将异步函数的结果作为函数结果返回.您需要传递一个在函数完成时运行的完成处理程序，该代码是可以访问结果的代码.

You've hinted at your problem, but not stated it explicitly. The deal is that you can't return the result of an async function as a function result. You need to pass in a completion handler that runs when the function finishes, and that code is the code that has access to the result.

returnFunction() -> (Double) {

  getChartIndexValues() { (zero) -> () in

    //Your code to process the results belongs here
    self.someInstanceVar = zero
    someLabel.text = "Your result is \(zero)"
    }

}
//You CAN'T put your code to process results here.

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