CODEWITHSUNDEEP
swiftswiftuiswift5
A Abhishek
A Abhishek

Reputation: 77

Fetching JSON data after implementing JSON web service

I am learning Swift on Udemy and JSON data parsing has me struggling. I have created two files WebService.swift and OrderListViewModel.swift. Former is... as name suggests implementing the data request (node.js) from Glitch while later is implementing View Model. Here are the files:

`WebService.swift`:



import Foundation

class Webservice {

    func getAllOrders(completion: @escaping ([Order]?) -> ()) {

        guard let url = URL(string: "https://island-bramble.glitch.me/orders") else {
            completion(nil)
            return
        }

       let task = URLSession.shared.dataTask(with: url) { data, response, error in

            guard let data = data, error == nil else {
                DispatchQueue.main.async {
                  completion(nil)
                }

                return

            }


            let orders = try? JSONDecoder().decode([Order].self, from: data)
            DispatchQueue.main.async {
                completion(orders)
            }

       }.resume()

    }
}

I reasonably understand what's happening here. I am unable to understand the part that's happening below. 

`OrderListViewModel.swift`:

import Foundation


    class OrderListViewModel: ObservableObject {


        var orders = [OrderViewModel]()

        init() {
            fetchOrders()
        }
        func fetchOrders() {

            Webservice().getAllOrders { orders in
                if let orders = orders {
                    self.orders = orders.map(OrderViewModel.init)
            }

            }
        }
    }

    class OrderViewModel {

        let id = UUID()

        var order: Order
        init (order: Order) {
            self.order = order
        }
        var name: String {
            return self.order.name
        }
        var size: String {
            return self.order.size
        }
        var coffeeName: String {
            return self.order.coffeeName
        }
        var total: Double {
            return self.order.total
        }
    }

How is fetchOrders() fetching orders. More specifically how is this block of code (closure) fetching the orders? Alternatively, if data fetched from remote server is passed as arguments to the callback function’s parameters how is below code retrieving it? 

 Webservice().getAllOrders { orders in
                if let orders = orders {
                    self.orders = orders.map(OrderViewModel.init)
            }

Upvotes: 2

Views: 94

Answers (1)

dywp
dywp

Reputation: 123

You call a function

Webservice().getAllOrders

and pass a completion block 

{ orders in
    if let orders = orders {
          self.orders = orders.map(OrderViewModel.init)
}

into it.

Completion block will receive value named orders of type [Order]?

and if orders is not nil

if let orders = orders

You can assign your class var orders, which is declared here

var orders = [OrderViewModel]

to new array which in turn contains elements of type OrderViewModel

The latter is the result of

orders.map(OrderViewModel.init)

and this can also be written like 

orders.forEach { order in 
      self.orders.append(OrderViewModel.init(order))
}

Upvotes: 1

Related Questions