Swift calling completion handler in from another file fails - swift

Question

I am calling a funciton with completio=n handler from one calss to another class
Called class:
class PVClass
{
var avgMonthlyAcKw:Double = 0.0
var jsonString:String!
func estimateMonthlyACkW (areaSqFt:Float, completion: #escaping(Double) -> () ){
var capacityStr:String = ""
let estimatedCapacity = Float(areaSqFt/66.0)
capacityStr = String(format: "%.2f", estimatedCapacity)
// Build some Url string
var urlString:String = "https://developer.nrel.gov/"
urlString.append("&system_capacity=")
urlString.append(capacityStr)
let pvURL = URL(string: urlString)
let dataTask = URLSession.shared.dataTask(with: pvURL!) { data, response, error in
do {
let _ = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers)
self.jsonString = String(data: data!, encoding: .utf8)!
print("JSON String:\(String(describing: self.jsonString))")
if self.jsonString != nil {
let decoder = JSONDecoder()
let jsonData = try decoder.decode(PVClass.Top.self, from: data!)
// do some parsing here
var totalAcKw: Double = 0.0
let cnt2: Int = (jsonData.Outputs?.ACMonthly.count)!
for i in 0..<(cnt2-1) {
totalAcKw = totalAcKw + (jsonData.Outputs?.ACMonthly[i])!
}
self.avgMonthlyAcKw = Double(totalAcKw)/Double(cnt2)
// prints value
print("updated estimate: ", self.avgMonthlyAcKw)
}
} catch {
print("error: \(error.localizedDescription)")
}
}
dataTask.resume()
completion(self.avgMonthlyAcKw)
}
Calling Class:
func estimate() {
var estimatedSolarkWh:Double = 0.0
let aPVClass = PVClass()
aPVClass.estimateMonthlyACkW(areaSqFt: 100.0, completion: { (monthlyAckW) -> Void in
estimatedSolarkWh = monthlyAckW
self.view.setNeedsDisplay()
})
return
}
}
When I call the function estimate() the estimateMonthlyACkW function in the other PVClass is executed but it returns after the calling estimate() function is executed. So even though in the called function the URLsession is executed, json is parsed, and value is printed correctly - the value never gets gets transferred to the completion handler and the value never comes back to calling class. How can I fix this?

Answer 1

You need to move completion(self.avgMonthlyAcKw) just after print statement like below:
// prints value
print("updated estimate: ", self.avgMonthlyAcKw)
completion(self.avgMonthlyAcKw)
Hope this will helps you :)