Using the returned value of a function - Swift

Question

I have written this code (In the function I am using the SwiftSky Api)

// Asked question about WEATHER

public func weatherQuestion(question: String, userLatitude: Double, userLongitude: Double) -> String {

 var answer = String()

// Setting up SwiftSky

 SwiftSky.secret ="...."

 SwiftSky.language = .italian

 SwiftSky.locale = .current

 SwiftSky.units.temperature = .celsius
 SwiftSky.units.accumulation = .centimeter
 SwiftSky.units.distance = .kilometer
 SwiftSky.units.precipitation = .millimeter
 SwiftSky.units.pressure = .millibar
 SwiftSky.units.speed = .kilometerPerHour

 if question.contains("meteo") {

     SwiftSky.get([.current, .alerts, .days, .hours, .minutes], at:  Location(latitude: userLatitude, longitude: userLongitude) , on: Date() , { (result) in

         switch result {

         case .success(let forecast):

             answer = (forecast.current?.summary)!

         case .failure(let error):

             print(error)

         }

     })

 }

 return answer
}

The problem is that, when I try to use the result of the function by printing its value (using the code below)

print(weatherQuestion(question: text, userLatitude: Double(self.locationCoordinates.latitude), userLongitude: Double(self.locationCoordinates.longitude)))

it doesn't print anything. How can I use the result of the function so that when I print out the value it is not empty?

`SwiftSky` works asynchronously. You cannot return something in a function from an asynchronous task. You have to add a completion handler. — vadian, Sep 03 '17 at 10:36
how can I do it? @vadian (Sorry but I am new to programming) — edoriggio, Sep 03 '17 at 10:36
Please look at (for example, there are many many similar answers) https://stackoverflow.com/questions/39643334/how-do-you-write-a-completion-handler-in-swift-3/39643395#39643395 — vadian, Sep 03 '17 at 10:39
@Moritz You're right, I knew about it... . Thank you all for the help — edoriggio, Sep 03 '17 at 10:41

score 1 · Accepted Answer · answered Sep 03 '17 at 10:35

SwiftSky.get works async and calls the passed closure with the result parameter when operation is done. So, weatherQuestion returns immediately.

Change method signature to:

public func weatherQuestion(question: String, userLatitude: Double, userLongitude: Double, completion: (String) -> Void)

and call it:

case .success(let forecast):
     completion(forecast.current!.summary)

Now print in completion:

weatherQuestion(question: text, userLatitude: Double(self.locationCoordinates.latitude), userLongitude: Double(self.locationCoordinates.longitude), completion: { answer in
      print(answer)
})

It works flawlessly! Thank you so much for your help – edoriggio Sep 03 '17 at 10:50 — edoriggio, Sep 03 '17 at 10:50

Using the returned value of a function - Swift

1 Answers1