How to get json data for passing it by segue - ios

Question

I try to get json data while URLSession.dataTask is running to set segue .(each json data as sender)
So First, I made my own Class Array productList = [Product]().
Next, I call getJsonData() and inside of that, I set URLSession.dataTask method. So I got Parsed json data. However, When I try to save that json data(append each data to productList) from dataTask completionHandler, it cannot save correctly.(result productList is [])
I want to pass parsed json data by segue. How can I do this?
edited --
class MainVC: UITableViewController {
var productList = [Product]()
override func viewDidLoad() {
super.viewDidLoad()
getJsonData()
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return productList.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if let cell = tableView.dequeueReusableCell(withIdentifier: "ItemCell", for: indexPath) as? ItemCell {
let product = productList[indexPath.row]
cell.configureCell(product)
return cell
} else {
return UITableViewCell()
}
}
func getJsonData() {
let url = URL(string: "http://demo7367352.mockable.io")
let request = URLRequest(url: url!)
let defaultSession = URLSession(configuration: URLSessionConfiguration.default)
let task = defaultSession.dataTask(with: request, completionHandler: { (data, response, error) in
do {
guard let data = data, error == nil else {
print("network request failed: error = \(error)")
return
}
guard let rawItem = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] else {
print("error trying to convert data to JSON")
return
}
if let fineItem = rawItem["goods"] as? [[String:Any]] {
for item in fineItem {
let eachProduct = Product(title: "", price: 0)
let title = item["TITLE"]
let price = item["PRICE"]
let regDate = item["REGDATE"]
let description = item["DESCRIPTION"]
let iconURL = item["ICON_URL"]
let images = item["IMAGES"]
if let title = title as? String {
eachProduct.title = title
}
if let price = price as? String {
eachProduct.price = Int(price)!
}
DispatchQueue.main.async(execute: {
self.productList.append(eachProduct)
self.tableView.reloadData()
})
}
}
} catch {
print("error trying to convert data to JSON")
return
}
})
task.resume()
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToProductDetail" {
if let controller = segue.destination as? DetailVC, let indexPath = tableView.indexPathForSelectedRow {
}
}
}
}
Right now, I can parse datas from URLSession DataTask. I want to implement segue of tableView to show detail. But productList is empty. So I cannot use prepareForSegue with productList[indexPath.row].
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToProductDetail" {
if let controller = segue.destination as? DetailVC, let indexPath = tableView.indexPathForSelectedRow {
controller.product = productList[indexPath.row] // productList is nil.
}
}
}

Answer 1

You need to implement prepare(for:sender:) and pass the data there:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let controller = segue.destination as? MySecondViewController, indexPath = tableView.indexPathForSelectedRow {
controller.product = productList[indexPath.row]
}
}
The exact syntax will vary (what is the class name of your destination view controller) and you'd have to declare that product property in the destination, and the destination's viewDidLoad would need to use that property, but hopefully it illustrates the basic idea.
Some additional observations:
I'd suggest you inspect rawItem and make sure it's a dictionary that has a key called goods and that the value associated with that key is really an array of dictionaries. Without seeing your JSON, it's impossible to say what exactly is going wrong.
Also, consider:
if let fineItem = rawItem["goods"] as? [[String:Any]] {
...
}
If that fails, you'll never know. I might instead suggest:
guard let fineItem = rawItem["goods"] as? [[String:Any]] else {
print("goods not found or wrong type")
return
}
...
BTW, and unrelated to your problem at hand, it's a little dangerous to be mutating productList directly in the completion handler of your data task. Don't asynchronously mutate arrays from one thread that are read from another thread. Arrays are not thread-safe. The data task completion handler should build a local array and only when it's done, inside where you're dispatching the reload to the main queue, you should insert code to replace the productList with your local array before the table is reloaded.
Also, you're currently calling reloadData inside the parsing loop. You'd generally call it at the end of the parsing loop. Right now, if your data set had 100 rows, you'd be reloading the table 100 times.
The reference to data! is a bit dangerous. If you have no internet connection, data will be nil and your code will crash. I'd suggest:
guard let data = data, error == nil else {
print("network request failed: error = \(error)")
return
}
And then you can replace the data! reference with data.

Answer 2

You aren't posting all of your code, but I believe that your mistake is that you are performing an asynchronous task and then immediately calling print on the array being modified. I wouldn't expect the array to be populated until the task is complete.
Does your tableView actually populate with results? Are you printing out the JSON to ensure that your data is matching properly? Are the errors being printed?
Edit:
To pass your data along the segue you need to retrieve your destinationViewController as a variable and pass the information to it. There is a method called prepareForSegue that allows you to handle the preliminary state before your action happens.
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let vc = segue.destination as! ExampleVC
vc.setProducts(productList)
}
Something like that. Obviously changing your class and variable names

Answer 3

I solved my Problem and here is my final code.
class MainVC: UITableViewController {
var productList = [Product]()
override func viewDidLoad() {
super.viewDidLoad()
getJsonData()
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return productList.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if let cell = tableView.dequeueReusableCell(withIdentifier: "ItemCell", for: indexPath) as? ItemCell {
let product = productList[indexPath.row]
cell.configureCell(product)
return cell
} else {
return UITableViewCell()
}
}
// parsing
func getJsonData() {
let url = URL(string: "http://demo7367352.mockable.io")
let request = URLRequest(url: url!)
let defaultSession = URLSession(configuration: URLSessionConfiguration.default)
let task = defaultSession.dataTask(with: request, completionHandler: { (data, response, error) in
do {
guard let data = data, error == nil else {
print("network request failed: error = \(error)")
return
}
guard let rawItem = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] else {
print("error trying to convert data to JSON")
return
}
guard let fineItem = rawItem["goods"] as? [[String:Any]] else {
print("goods not found or wrong type")
return
}
for item in fineItem {
let eachProduct = Product(title: "", price: 0)
let title = item["TITLE"]
let price = item["PRICE"]
if let title = title as? String {
eachProduct.title = title
}
if let price = price as? String {
eachProduct.price = Int(price)!
}
self.productList.append(eachProduct)
}
DispatchQueue.main.async(execute: {
self.tableView.reloadData()
})
} catch {
print("error trying to convert data to JSON")
return
}
})
task.resume()
}
// segue
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToProductDetail" {
if let controller = segue.destination as? DetailVC, let indexPath = tableView.indexPathForSelectedRow {
controller.product = productList[indexPath.row]
}
}
}
}