Modern code for making HTTP requests in Swift 5 using Combine and using them in SwiftUI. Part 1

NewsAPI.org Service Data Model and API

import Foundation

struct NewsResponse: Codable {
    let status: String?
    let totalResults: Int?
    let articles: [Article]
}

struct Article: Codable, Identifiable {
    let id = UUID()
    let title: String
    let description: String?
    let author: String?
    let urlToImage: String?
    let publishedAt: Date?
    let source: Source
}

struct SourcesResponse: Codable {
    let status: String
    let sources: [Source]
}

struct Source: Codable,Identifiable {
    let id: String?
    let name: String?
    let description: String?
    let country: String?
    let category: String?
    let url: String?
}

• fetchArticles (from endpoint: Endpoint) -> AnyPublisher<[Article], Never>  - selection of articles  [Article]based on the parameter endpoint,
• fetchSources (for country: String) -> AnyPublisher<[Source], Never>- A selection of sources of information [Source]for a particular country country.

enum Endpoint {
    case topHeadLines
    case articlesFromCategory(_ category: String)
    case articlesFromSource(_ source: String)
    case search (searchFilter: String)
    case sources (country: String)
    
    var baseURL:URL {URL(string: "https://newsapi.org/v2/")!}
    
    func path() -> String {
        switch self {
        case .topHeadLines, .articlesFromCategory:
            return "top-headlines"
        case .search,.articlesFromSource:
            return "everything"
        case .sources:
            return "sources"
        }
    }
}

• the latest news  .topHeadLines,
• news of a certain category (sports, healthy, science, business, technology)  .articlesFromCategory(_ category: String),
• news from a specific source of information (CNN, ABC News, Fox News, etc.)  .articlesFromSource(_ source: String),
• any news  .search (searchFilter: String)that meets a certain condition searchFilter,
• sources of information .sources (country:String)for a particular country country.

init? (index: Int, text: String = "sports") {
        switch index {
        case 0: self = .topHeadLines
        case 1: self = .search(searchFilter: text)
        case 2: self = .articlesFromCategory(text)
        case 3: self = .articlesFromSource(text)
        case 4: self = .sources (country: text)
        default: return nil
        }
    }

func fetchArticles(from endpoint: Endpoint) -> AnyPublisher<[Article], Never> {
        guard let url = endpoint.absoluteURL else {              // 0
                    return Just([Article]()).eraseToAnyPublisher()
        }
           return
            URLSession.shared.dataTaskPublisher(for:url)        // 1
            .map{$0.data}                                       // 2
            .decode(type: NewsResponse.self,                    // 3
                    decoder: APIConstants .jsonDecoder)
            .map{$0.articles}                                   // 4
            .replaceError(with: [])                             // 5
            .receive(on: RunLoop.main)                          // 6
            .eraseToAnyPublisher()                              // 7
    }

• on the basis of the endpoint form URLfor the request the desired list of articles endpoint.absoluteURL, if this could not be done, then return an empty array of articles[Article]()
• «» dataTaskPublisher(for:), Output (data: Data, response: URLResponse),   Failure - URLError,
• map { } (data: Data, response: URLResponse)  data, 
• JSON  data ,  NewsResponse, articles: [Atricle]
• map { }  - articles, 
• - [ ],
• main , UI,
• «» «» eraseToAnyPublisher() AnyPublisher.

func fetchSources() -> AnyPublisher<[Source], Never> {
        guard let url = Endpoint.sources.absoluteURL else {      // 0
                       return Just([Source]()).eraseToAnyPublisher()
           }
              return
               URLSession.shared.dataTaskPublisher(for:url)      // 1
               .map{$0.data}                                     // 2
               .decode(type: SourcesResponse.self,               // 3
                       decoder: APIConstants .jsonDecoder)
               .map{$0.sources}                                  // 4
               .replaceError(with: [])                           // 5
               .receive(on: RunLoop.main)                        // 6
               .eraseToAnyPublisher()                            // 7
    }

//     URL
     func fetch<T: Decodable>(_ url: URL) -> AnyPublisher<T, Error> {
                   URLSession.shared.dataTaskPublisher(for: url)             // 1
                    .map { $0.data}                                          // 2
                    .decode(type: T.self, decoder: APIConstants.jsonDecoder) // 3
                    .receive(on: RunLoop.main)                               // 4
                    .eraseToAnyPublisher()                                   // 5
    }

//   
     func fetchArticles(from endpoint: Endpoint)
                                     -> AnyPublisher<[Article], Never> {
         guard let url = endpoint.absoluteURL else {
                     return Just([Article]()).eraseToAnyPublisher() // 0
         }
         return fetch(url)                                          // 1
             .map { (response: NewsResponse) -> [Article] in        // 2
                             return response.articles }
                .replaceError(with: [Article]())                    // 3
                .eraseToAnyPublisher()                              // 4
     }
    
    //    
    func fetchSources(for country: String)
                                       -> AnyPublisher<[Source], Never> {
        guard let url = Endpoint.sources(country: country).absoluteURL
            else {
                    return Just([Source]()).eraseToAnyPublisher() // 0
        }
        return fetch(url)                                         // 1
            .map { (response: SourcesResponse) -> [Source] in     // 2
                            response.sources }
               .replaceError(with: [Source]())                    // 3
               .eraseToAnyPublisher()                             // 4
    }

"Publishers" Publisheras View Model in SwiftUI. List of articles.

• @Published var indexEndpoint: Int — Endpoint ( «», View),  
• @Published var searchString: String — ,   ( «», View  TextField),
• @Published var articles: [Article] - ( «», NewsAPI.org, «»).

List of sources of information

• text box  SearchViewfor the search bar  searchString,
•  Picker for the country country,
• list of  SourcesList sources of information

• index  indexEndpoint = 3, that is, an option  .articlesFromSource (_source:String)corresponding to the selection of articles for a fixed source source,
• string  searchString as the source itself (or rather its identifier) source.id :

Download image UIImagefor article Article.

1. if urlequal nil, return Just(nil),
2. based on the urlform of the "publisher" dataTaskPublisher(for:), whose output value Outputis a tuple (data: Data, response: URLResponse)and an error  Failure-  URLError,
3. we take only data map {}from the tuple (data: Data, response: URLResponse)for further processing  data, and form UIImage,
4. if the previous steps return error occurs nil,
5. we deliver the result to the mainstream, as we assume further use in the design UI,
6. “Erase” the TYPE of the “publisher” and return the copy AnyPublisher.

• @Published url: URL? are URLimages
• @Published var image: UIImage? is the image itself from NewsAPI.org :

Display errors when fetching and decoding JSON data from the NewsAPI.org server  .

func fetchArticlesErr(from endpoint: Endpoint) ->
                            AnyPublisher<[Article], NewsError> {

. . . . . . . .
}

• 0. endpoint  URL endpoint.absoluteURL , url nil: nil, .urlError, — url ,
• 1. «» dataTaskPublisher(for:), — url, Output (data: Data, response: URLResponse)  URLError,
• 2. tryMap { }  (data: Data, response: URLResponse): response.statusCode 200...299,  data. «» .responseError,   data, String, ,
• 3. JSON ,  NewsResponse,
• 4. main , UI
• «» «» sink receiveCompletion receiveValue,
  
  • 5.    receiveCompletion  error, promise (.failure(...))),
  • 6.   receiveValue promise (.success($0.articles)),
   
• 7.  «»  var subscriptions, « » NewsAPI,
• 8. «» «» AnyPublisher.

1. @Published var indexEndpoint: Int — Endpoint ( «», View), 
2. @Published var searchString: String — ,  Endpoint: «» , ( «», View), 
3.  @Published var articles: [Article] - ( «»,  NewsAPI.org )
4.   @Published var articlesError: NewsError? - ,    NewsAPI.org .

struct APIConstants {
    // News  API key url: https://newsapi.org
    static let apiKey: String = "API_KEY" 
    
   .  .  .  .  .  .  .  .  .  .  .  .  .
}

Conclusion

References: