Swift 4 - 结构静态变量不显示值

Question

我是 Swift 新手，但不断学习。我有一个使用 for..loop 从 AWS DynamoDB 表获取数据的函数。我正在循环内的结构变量中捕获表项的字段值，但是当我在 TableView 中调用结构变量时，它在 Xcode 的日志屏幕中显示空白数组，如 [] 。这是代码:

<小时/>

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
    }
}

后来，我在 TableView 中调用这个DatabaseClass，如下所示:

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

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

在模拟器中运行时，日志文件显示以下内容:

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]]

在执行函数scanEmployees时，它似乎跳过了DynamoDB扫描命令并在tableview中返回[]，但以某种方式转到该函数并执行数据。它无法捕获结构变量中的数据。我已经尝试解决这个问题很多天了。

Answer 1

您的静态内存有问题。我建议不要使用静态值，这是一个非常糟糕的做法。解决方案可能是在 DatabaseClass 类中创建一个结构。例如 var myVariables = MyVariables() 并以相同的方式填充它。现在您可以选择返回它或从 DatabaseClass 对象使用它。我现在将展示该示例它应该是什么样子。

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)

         }
      }