Swift 3 Parse JSON into UITableView using URLSession - json

Question

I am trying to parse JSON using URLSession and without using Alamofire or anything else.
I just want to take the JSON and put it into a UITableView.
I am trying to piece together what I learned from learning how to Parse JSON using Alamofire with what I can find on google. Many of the answers on youtube or Stack etc use NS for everything..NSURL, NSDictionary, etc etc..Or are just typing code without explaining what/why.
I THINK I am almost there, but I need help understanding what I have left to do.
SO.
I Allowed arbitrary loads in the plst
In a Swift File I have the following
class Potter {
private var _title: String!
private var _author: String!
private var _imageURL: String!
let POTTER_URL = "http://de-coding-test.s3.amazonaws.com/books.json"
var title: String {
if _title == nil {
_title = ""
}
return _title
}
var author: String {
if _author == nil {
_author = ""
}
return _author
}
var imageURL: String {
if _imageURL == nil {
_imageURL = ""
}
return _imageURL
}
func downloadJSON() {
let url = URL(string: POTTER_URL)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil {
print("Error")
} else {
if let content = data {
do {
if let jDict = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as? Dictionary<String, AnyObject> {
if let title = jDict["title"] as? String {
self._title = title.capitalized
}
if let author = jDict["author"] as? String {
self._author = author.capitalized
}
if let imgURL = jDict["imageURL"] as? String {
self._imageURL = imgURL
}
}
}
catch {
}
}
}
}
task.resume()
}
}
In my Main.Storyboard I added the tableview and set up all the UI, and in my ViewController I have set up the tableview delegates.
I created a property of
var potters = [Potter]()
I am stuck now on how to I populate this array, and how do I set up the proper threading

Answer 1

First of all your model is insane pretty weird.
In Swift never use backed private variables to get read/only properties. And never declare properties as implicit unwrapped optional because you are too lazy to write an initializer.
The entire model can be reduced to
class Potter {
let title, author, imageURL: String
init(title: String, author: String, imageURL : String) {
self.title = title
self.author = author
self.imageURL = imageURL
}
}
If you would use a struct, it's even
struct Potter {
let title, author, imageURL: String
}
because you get the memberwise initializer for free.
Secondly, put the method downloadJSON() out of the model and put it in the controller and call it in viewDidLoad().
In the controller declare the download URL and the data source array
let POTTER_URL = "http://de-coding-test.s3.amazonaws.com/books.json"
var books = [Potter]()
Your method downloadJSON() cannot work because the JSON object is an array ([]), not a dictionary ({}). You need a loop to iterate thru the items, get the values, create a Potter item respectively and append it to the data source. If a value does not exist, an empty string is assigned. Finally reload the table view on the main thread.
func downloadJSON() {
let url = URL(string: POTTER_URL)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil {
print("DataTask error", error!)
} else {
do {
if let bookData = try JSONSerialization.jsonObject(with: data!) as? [[String:String]] {
books.removeAll() // clear data source array
for book in bookData {
let title = book["title"] ?? ""
let author = book["author"] ?? ""
let imgURL = book["imageURL"] ?? ""
books.append(Potter(title: title, author: author, imageURL: imgURL))
}
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
}
catch {
print("Serialization error", error)
}
}
}
task.resume()
}
Two notes:
The standard JSON dictionary in Swift 3 is [String:Any], in this particular case it's even [String:String].
.mutableContainers is useless if the containers are only read and useless in Swift anyway because the object cannot be casted to NSMutableArray / -Dictionary and you get mutability for free using a variable.

Answer 2

The web services returns an array of objects: [Dictionary<String, AnyObject>].
It will be easier if you create a init method with a dictionary as parameter.
The downloadJSON is an async task, using completionHandler is the best way. And if you want to place the downloadJSON in the Potter class, it should be a static function.
Final, you should handle the result like this:
Potter.downloadJSON { potters in
self.potters = potters
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
The final code:
class ViewController: UIViewController {
var potters = [Potter]()
#IBOutlet weak var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
Potter.downloadJSON { potters in
self.potters = potters
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
}
}
extension ViewController: UITableViewDelegate, UITableViewDataSource {
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return potters.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell")!
let potter = potters[indexPath.row]
cell.textLabel?.text = potter.title
cell.detailTextLabel?.text = potter.author
return cell
}
}
class Potter {
private var _title: String!
private var _author: String!
private var _imageURL: String!
static let POTTER_URL = "http://de-coding-test.s3.amazonaws.com/books.json"
var title: String {
if _title == nil {
_title = ""
}
return _title
}
var author: String {
if _author == nil {
_author = ""
}
return _author
}
var imageURL: String {
if _imageURL == nil {
_imageURL = ""
}
return _imageURL
}
init(dict: Dictionary<String, AnyObject>) {
self._title = dict["title"] as? String
self._imageURL = dict["imageURL"] as? String
self._author = dict["author"] as? String
}
class func downloadJSON(completion: #escaping (_ potters: [Potter]) -> Void) {
let url = URL(string: POTTER_URL)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil {
print("Error")
} else {
if let content = data {
do {
if let jArray = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as? [Dictionary<String, AnyObject>] {
var potters = [Potter]()
for jDict in jArray {
let potter = Potter(dict: jDict)
potters.append(potter)
}
completion(potters)
}
}
catch {
}
}
}
}
task.resume()
}
}

Answer 3

The method downloadJSON() should be implemented in the ViewController since it is returning the array of Potter data. Then in the URLSession response you should create one array which will be act as the tableview datasource. (i.e self.arrTableData = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as? [[String : AnyObject]])
Then in for the tableView
func tableView(_ tableView: UITableView, numberOfRowsInSection sectionIndex: Int) -> Int {
return self.arrTableData.count
}
and in cell for row at index path
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
//create `potters` object with the value and use it else you can direcly use the value of objects as below.
let dictPotters = self.arrTableData[indexPath.row]
let title = dictPotters["title"]
}
Thanks