How to wait and get results out completion of featureTable.queryFeatures

Question

I have a function must return a string, but my problem is Asynchronous Tasks. How to wait and get results out completion of featureTable.queryFeatures. Thanks! func GetValueSum(geo : AGSGeometry ) -> String{ var strReturn = "" let queryParameters = AGSQueryParameters() queryParameters.geometry = geo queryParameters.spatialRelationship = AGSSpatialRelationship.intersects queryParameters.outSpatialReference = self.mapView.spatialReference self.featureTable?.queryFeatures(with: queryParameters, completion: { (result: AGSFeatureQueryResult?, error: Error?) in if error != nil { print("Error in function") } else if let features = result?.featureEnumerator().allObjects { for feature in features { strReturn += "\(feature.attributes["Label1"]!); " print("For string: \(strReturn)") } } }) print("Return string: \(strReturn)") return strReturn }‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ The result: But the "Return string" must be the last "For string". Thanks for help!

Nicholas-Furness · Accepted Answer

Swift doesn't have an async keyword, so you'll need to structure your function not to return a string, but instead to require a callback block. Something like this: func getValueSum(geo : AGSGeometry, completion: @escaping (String)->Void) { let queryParameters = AGSQueryParameters() queryParameters.geometry = geo queryParameters.spatialRelationship = AGSSpatialRelationship.intersects queryParameters.outSpatialReference = self.mapView.spatialReference self.featureTable?.queryFeatures(with: queryParameters, completion: { (result: AGSFeatureQueryResult?, error: Error?) in var strReturn = "" if error != nil { print("Error in function") } else if let features = result?.featureEnumerator().allObjects { for feature in features { strReturn += "\(feature.attributes["Label1"]!); " print("For string: \(strReturn)") } } completion(strReturn) }) } ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ // Call like this, and do operations on the result in the callback block… getValueSum(geo: geometry) { allLabels in print("Got all the labels: \(allLabels)") } ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍