Swift 4 - Struct static variables not showing values

Question

I am new to swift but learning as I go. I have a function to get data from AWS DynamoDB table, using a for..loop. I am capturing field values of table items in struct variables within the loop, but when I call the struct variables in a tableview, it is showing blank array like [] in the log screen in Xcode. Here is the code:

---

import Foundation
import SQLite3
import UIKit
import AWSDynamoDB

struct MyVariables {
    static var empDict: [String: String] = [:]
    static var arrayEmployees = Array<Dictionary<String, String>>()
}

// This is a class defined to hold various methods to be used throughout the app.
class DatabaseClass: UIViewController, UITextFieldDelegate
{
    // other methods within DatabaseClass
    // ........
    //
    //
    // Scan DynamoDB table for employees
    func scanEmployees () {
        let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
        let scanExpression = AWSDynamoDBScanExpression()
        scanExpression.limit = 20

        dynamoDBObjectMapper.scan(Employees.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
            if let error = task.error as NSError? {
                print("The request failed. Error: \(error)")
            }

            let paginatedOutput = task.result!

            for emp in paginatedOutput.items as! [Employees]  {
                if emp._empid != nil {
                    MyVariables.empDict["Empid"] = emp._empid
                } else {
                    MyVariables.empDict["Empid"] = nil
                }

                if emp._email != nil {
                    MyVariables.empDict["email"] = emp._email
                } else {
                    MyVariables.empDict["email"] = nil
                }

                if emp._firstname != nil {
                    MyVariables.empDict["firstname"] = emp._firstname
                } else {
                    MyVariables.empDict["firstname"] = nil
                }

                if emp._lastname != nil {
                    MyVariables.empDict["lastname"] = emp._lastname
                } else {
                    MyVariables.empDict["lastname"] = nil
                }

                if emp._location != nil {
                    MyVariables.empDict["location"] = emp._location
                } else {
                    MyVariables.empDict["location"] = nil
                }

                if emp._mobile != nil {
                    MyVariables.empDict["mobile"] = emp._mobile
                } else {
                    MyVariables.empDict["mobile"] = nil
                }

                if emp._work != nil {
                    MyVariables.empDict["work"] = emp._work
                } else {
                    MyVariables.empDict["work"] = nil
                }

                if emp._site != nil {
                    MyVariables.empDict["site"] = emp._site
                } else {
                    MyVariables.empDict["site"] = nil
                }

                MyVariables.arrayEmployees.append(MyVariables.empDict)
                //print(MyVariables.arrayEmployees)
            } // for loop

            print ("printing array employees just after for loop")
            print(MyVariables.arrayEmployees)
            // The above print works

            return nil
        })

        // print(MyVariables.arrayEmployees)
        // Above doesn’t print
    }
}

Later, I call this DatabaseClass in a tableview as follows:

class JsonParseViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let createEmp = DatabaseClass()
        createEmp.scanEmployees()
        print("in JsonParseViewController, calling scan function")
        print(MyVariables.arrayEmployees)

When running in simulator, the log file shows the following:

in JsonParseViewController, calling scan function
[]
printing array employees just after for loop
[["location": "XXXXXX", "email": "johnSmith1@email.com", "firstname": "John1", "lastname": "Smith1", "mobile": "123-456-7890", "work": "123-456-7890", "Empid": "12345", "site": "KKKKKK"], ["location": "YYYYY", "email": "johnSmith8@email.com", "firstname": "John8", "lastname": "Smith8", "mobile": "123-456-7890", "work": "123-456-7890", "Empid": "12415", "site": "ZZZZZ"], ......etc]]

While executing the function scanEmployees, it seems to skip the DynamoDB scan command and returns [] in tableview, but goes to the function somehow and executes the data. It fails to capture the data in struct variables. I have bee trying to fix this for many days.

Answer 1

You miss asynchronous call

func scanEmployees (completion:@escaping ()-> Void) {

    let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
    let scanExpression = AWSDynamoDBScanExpression()
    scanExpression.limit = 20

    dynamoDBObjectMapper.scan(Employees.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in

        if let error = task.error as NSError? {
            print("The request failed. Error: \(error)")
        }

        let paginatedOutput = task.result! 

            for emp in paginatedOutput.items as! [Employees]  {

                myVariables.empDict["Empid"] = emp._empid
                myVariables.empDict["email"] = emp._email
                myVariables.empDict["firstname"] = emp._firstname
                myVariables.empDict["lastname"] = emp._lastname
                myVariables.empDict["location"] = emp._location
                myVariables.empDict["mobile"] = emp._mobile
                myVariables.empDict["work"] = emp._work
                myVariables.empDict["site"] = emp._site

                MyVariables.arrayEmployees.append(MyVariables.empDict)
                //print(MyVariables.arrayEmployees)

            } // for loop
                print ("printing array employees just after for loop")
                print(MyVariables.arrayEmployees)
              // The above print works

             completion()
             return nil
   } 
 ) 

   // print(MyVariables.arrayEmployees)
   // Above doesn’t print
} 

//

when calling

createEmp.scanEmployees {

       print(MyVariables.arrayEmployees)
}

Note : I recommend using SwiftyJson or JSONDecoder intstead of manually parsing the keys

Answer 2

You have a problem with static memory. I would suggest not to use static values, its a very bad practice. The solution could be to create a structure inside The class DatabaseClass. For example var myVariables = MyVariables() and fill it in the same way. Now You have the option for return it or use it from the DatabaseClass object. I will show the example now how it should look.

struct MyVariables {
    var empDict: [String: String] = [:]
    var arrayEmployees = Array<Dictionary<String, String>>()
}

// This is a class defined to hold various methods to be used throughout the app.
class DatabaseClass: UIViewController, UITextFieldDelegate
{
    // other methods within DatabaseClass
    // ........
    //
    //
    // Scan DynamoDB table for employees
  public var myVariables = MyVariables()

 func scanEmployees () {
        let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
        let scanExpression = AWSDynamoDBScanExpression()
        scanExpression.limit = 20

        dynamoDBObjectMapper.scan(Employees.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
            if let error = task.error as NSError? {
                print("The request failed. Error: \(error)")
            }

            let paginatedOutput = task.result!

            for emp in paginatedOutput.items as! [Employees]  {
                myVariables.empDict["Empid"] = emp._empid
                myVariables.empDict["email"] = emp._email
                myVariables.empDict["firstname"] = emp._firstname
                myVariables.empDict["lastname"] = emp._lastname
                myVariables.empDict["location"] = emp._location
                myVariables.empDict["mobile"] = emp._mobile
                myVariables.empDict["work"] = emp._work
                myVariables.empDict["site"] = emp._site

                myVariables.arrayEmployees.append(myVariables.empDict)
                //print(myVariables.arrayEmployees)
            } // for loop

            print ("printing array employees just after for loop")
            print(myVariables.arrayEmployees)
            // The above print works

            return nil
        })

        // print(myVariables.arrayEmployees)
        // Above doesn’t print
    }
}

//then use it in this way


    class JsonParseViewController: UIViewController {
        override func viewDidLoad() {
            super.viewDidLoad()

            let createEmp = DatabaseClass()
            createEmp.scanEmployees()
            print("in JsonParseViewController, calling scan function")
            print(createEmp.myVariables.arrayEmployees)

         }
      }