In this tutorial we will create a simple application that demonstrates the use of URLSession and URLSessionDataTask in Swift 3.1
Note: As this article focusses primarily on the above stated aspects we will leave some UI functionality like showing a progress indicator when the web service is being called out of the scope of this post.
We will have a cocoa application that has two view based NSTableView. In one of the table view we will show a list of food menu items and once the user clicks one of the food menu item we will trigger a webservice call to get the list of sub menu items/ dishes for the selected food category.
Earlier while taking a course in angularjs at Coursera, I had created two webservices and will be using the same here.
https://knowstack-angularjs.herokuapp.com/categories.json gives a list of available menu items
https://knowstack-angularjs.herokuapp.com/menu_items.json?category=L gives the list of sub menu items/ dishes for a selected category.
Our final application will look as below
Swift 3.1 URLSession, URLSessionDataTask Sample Code
Lets get started with the code
Step 1: Create two classes that represent the response object for the two table views
class MenuItem{
var itemId:String?
var shortName:String?
var longName:String?
var specialInstructions:String?
var url:String?
}
class SubMenuItem{
var itemId: String?
var shortName:String?
var longName:String?
var itemDescription:String?
var priceSmall:String?
var priceLarge:String?
var smallPortionName:String?
var largePortionName:String?
}
Step 2: Create two NSTableCellView Subclasses for using in the ViewBased table views
class MenuItemTableCellView: NSTableCellView {
@IBOutlet weak var itemIdTextField: NSTextField!
@IBOutlet weak var shortNameTextField: NSTextField!
@IBOutlet weak var longNameTextField: NSTextField!
@IBOutlet weak var specialInstructionsTextField: NSTextField!
@IBOutlet weak var urlTextField: NSTextField!
}
class SubMenuItemTableCellView: NSTableCellView {
@IBOutlet weak var itemIdTextField: NSTextField!
@IBOutlet weak var shortNameTextField: NSTextField!
@IBOutlet weak var longNameTextField: NSTextField!
@IBOutlet weak var itemDescriptionTextField: NSTextField!
@IBOutlet weak var priceSmallTextField: NSTextField!
@IBOutlet weak var priceLargeTextField: NSTextField!
@IBOutlet weak var smallPortionNameTextField: NSTextField!
@IBOutlet weak var largePortionNameTextField: NSTextField!
}
Now lets have a look at the view controller which hosts the two table views and first web service is called when the view is loaded.
// ViewController.swift
// Swift-URLSession
// Created by Debasis Das on 5/24/17.
// Copyright © 2017 Knowstack. All rights reserved.
import Cocoa
class ViewController: NSViewController {
let menuItemURLString = "https://knowstack-angularjs.herokuapp.com/categories.json"
let subMenuItemURLString = "https://knowstack-angularjs.herokuapp.com/menu_items.json?category="
@IBOutlet weak var menuItemTableView:NSTableView!
@IBOutlet weak var subMenuItemTableView:NSTableView!
var menuItems = [MenuItem]()
var subMenuItems = [SubMenuItem]()
let defaultSession = URLSession(configuration: URLSessionConfiguration.default)
var dataTask:URLSessionDataTask?
var subMenuDataTask:URLSessionDataTask?
override func viewDidLoad() {
super.viewDidLoad()
menuItemTableView.delegate = self
subMenuItemTableView.delegate = self
menuItemTableView.dataSource = self
subMenuItemTableView.dataSource = self
loadMenuItems()
}
func loadMenuItems(){
menuItems = []
let searchURL = URL(string: menuItemURLString)
let urlRequest = URLRequest(url: searchURL!)
dataTask = defaultSession.dataTask(with: urlRequest, completionHandler: { (data, response, error) in
if let error = error {
print(error.localizedDescription)
}
self.updateMenuItems(data: data!)
})
dataTask?.resume()
}
func loadSubMenuItems(searchCriteia:String){
//print("loading sub menu items")
subMenuItems = []
let searchURL = URL(string: (subMenuItemURLString + searchCriteia))
let urlRequest = URLRequest(url: searchURL!)
//print(urlRequest)
subMenuDataTask = defaultSession.dataTask(with: urlRequest, completionHandler: { (data, response, error) in
if let error = error {
print(error.localizedDescription)
}
self.updateSubMenuItems(data: data!)
})
subMenuDataTask?.resume()
}
func updateMenuItems(data:Data?){
if let data = data{
do {
let response = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions(rawValue:0)) as! [AnyObject]
for item in response{
let newMenuItem = MenuItem()
newMenuItem.itemId = "\(String(describing: item["id"] as! Int))"
//newMenuItem.itemId = item["id"] as? String
newMenuItem.shortName = item["short_name"] as? String
newMenuItem.longName = item["name"] as? String
newMenuItem.specialInstructions = item["special_instructions"] as? String
newMenuItem.url = item["url"] as? String
menuItems.append(newMenuItem)
}
DispatchQueue.main.async {
print("updateSearchResults = \(Thread.isMainThread ? "Main Thread":"Background Thread")")
self.menuItemTableView.reloadData()
}
}
catch let error as NSError{
print("The error in the catch block is \(error)")
}
catch
{
print("Catch Block")
}
}
}
func updateSubMenuItems(data:Data?){
if let data = data{
do {
let response = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions(rawValue:0)) as! [String:AnyObject]
if let results = response["menu_items"] as? [AnyObject]{
for item in results{
let newSubMenu = SubMenuItem()
newSubMenu.itemId = "\(String(describing: item["id"] as! Int))"
newSubMenu.shortName = item["short_name"] as? String
newSubMenu.longName = item["name"] as? String
newSubMenu.itemDescription = item["description"] as? String
newSubMenu.priceSmall = item["price_small"] as? String//"\(String(describing: item["price_small"] as! Int))"
newSubMenu.priceLarge = item["price_large"] as? String//"\(String(describing: item["price_large"] as! Int))"
newSubMenu.smallPortionName = item["small_portion_name"] as? String
newSubMenu.largePortionName = item["large_portion_name"] as? String
subMenuItems.append(newSubMenu)
}
}
DispatchQueue.main.async {
print("updateSearchResults = \(Thread.isMainThread ? "Main Thread":"Background Thread")")
self.subMenuItemTableView.reloadData()
}
}
catch let error as NSError{
print("The error in the catch block is \(error)")
}
catch
{
print("Catch Block")
}
}
}
}
extension ViewController:NSTableViewDataSource, NSTableViewDelegate{
func numberOfRows(in tableView: NSTableView) -> Int {
switch tableView {
case menuItemTableView:
return menuItems.count
case subMenuItemTableView:
return subMenuItems.count
default:
return 0
}
}
func tableView(_ tableView: NSTableView, viewFor tableColumn: NSTableColumn?, row: Int) -> NSView?{
switch tableView {
case menuItemTableView:
let result:MenuItemTableCellView = tableView.make(withIdentifier: "defaultRow", owner: self) as! MenuItemTableCellView
result.itemIdTextField.stringValue = menuItems[row].itemId!
result.shortNameTextField.stringValue = menuItems[row].shortName!
result.longNameTextField.stringValue = menuItems[row].longName!
result.specialInstructionsTextField.stringValue = menuItems[row].specialInstructions!
result.urlTextField.stringValue = menuItems[row].url!
return result
case subMenuItemTableView:
let result:SubMenuItemTableCellView = tableView.make(withIdentifier: "defaultRow", owner: self) as! SubMenuItemTableCellView
result.itemIdTextField.stringValue = subMenuItems[row].itemId!
result.shortNameTextField.stringValue = subMenuItems[row].shortName!
result.longNameTextField.stringValue = subMenuItems[row].longName!
result.itemDescriptionTextField.stringValue = subMenuItems[row].itemDescription!
if let smallPrice = subMenuItems[row].priceSmall{
result.priceSmallTextField.stringValue = smallPrice
}
else{
result.priceSmallTextField.stringValue = "Unknown"
}
if let largePrice = subMenuItems[row].priceLarge{
result.priceLargeTextField.stringValue = largePrice
}
else{
result.priceLargeTextField.stringValue = "Unknown"
}
if let smallPortion = subMenuItems[row].smallPortionName{
result.smallPortionNameTextField.stringValue = smallPortion
}
else{
result.smallPortionNameTextField.stringValue = "Unknown"
}
if let largePortion = subMenuItems[row].largePortionName{
result.largePortionNameTextField.stringValue = largePortion
}
else{
result.largePortionNameTextField.stringValue = "Unknown"
}
return result
default:
return nil
}
}
func tableView(_ tableView: NSTableView, heightOfRow row: Int) -> CGFloat {
switch tableView {
case menuItemTableView:
return 140
case subMenuItemTableView:
return 80
default:
return 23
}
}
func tableViewSelectionDidChange(_ notification: Notification) {
if self.menuItemTableView == notification.object as? NSTableView{
//On selecting a menu item, the corresponding food items are retrieved and displayed on the second table
loadSubMenuItems(searchCriteia: menuItems[self.menuItemTableView.selectedRow].shortName!)
}
}
}
You can download the code from Swift-URLSession Sample Code
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