alexpaul / JSON-Examples

A repo for testing various JSON payloads.

JSON-Examples

A repo for testing various JSON payloads in various programming languages.

1. Using a JSON payload in Swift

1. Navigate to the .json file you're interested in using.
2. Copy the JSON contents.
3. Back in your Xcode project create a new file, select Empty file in the Xcode new file template.
4. Create a file with a similar name e.g presidents.json
5. Save this file in your App navigation folder.
6. Use the Bundle class to read the .json file and parse to your Swift object.

Make sure the JSON contents you copied starts on line 1 in your new file. It won't be valid JSON if there are new lines or any comments other than the JSON starting at the open bracket to the the last closed bracket.

2. Create the Swift Model that represents the JSON payload

struct President: Decodable {
  let number: Int
  let name: String
  let birthYear: Int
  let deathYear: Int
  let tookOffice: String
  let leftOffice: String
  let party: String
  
  private enum CodingKeys: String, CodingKey {
    case number
    case name = "president"
    case birthYear = "birth_year"
    case deathYear = "death_year"
    case tookOffice = "took_office"
    case leftOffice = "left_office"
    case party
  }
}

3. Unit Test the JSON payload along with your Swift model

func testModel() {
  // arrange
  let jsonData = """
  [{
     "number": 1,
     "president": "George Washington",
     "birth_year": 1732,
     "death_year": 1799,
     "took_office": "1789-04-30",
     "left_office": "1797-03-04",
     "party": "No Party"
   },
   {
     "number": 2,
     "president": "John Adams",
     "birth_year": 1735,
     "death_year": 1826,
     "took_office": "1797-03-04",
     "left_office": "1801-03-04",
     "party": "Federalist"
   }
  ]
  """.data(using: .utf8)!
  
  let expectedFirstPresident = "George Washington"
  
  // act
  do {
    let presidents = try JSONDecoder().decode([President].self, from: jsonData)
    let firstPresident = presidents[0]
    // assert
    XCTAssertEqual(firstPresident.name, expectedFirstPresident)
  } catch {
    XCTFail("decoding error: \(error)")
  }
}

4. Use the Bundle class to read the .json file and decode to Swift objects

enum BundleError: Error {
  case invalidResource(String)
  case noContentsAtPath(String)
  case decodingError(Error)
}

extension Bundle {
  func parseJSONFile(with name: String) throws -> [President] {
    guard let path = Bundle.main.path(forResource: name, ofType: ".json") else {
      throw BundleError.invalidResource(name)
    }
    guard let data = FileManager.default.contents(atPath: path) else {
      throw BundleError.noContentsAtPath(path)
    }
    var presidents: [President]
    do {
      presidents = try JSONDecoder().decode([President].self, from: data)
    } catch {
      throw BundleError.decodingError(error)
    }
    return presidents
  }
}

Generic parseJSONFile(with name:) method

Bundle+ParseJSON.swift

extension Bundle {
func parseJSONFile<T: Decodable>(with name: String) throws -> T {
  guard let path = Bundle.main.path(forResource: name, ofType: ".json") else {
    throw BundleError.invalidResource(name)
  }
  guard let data = FileManager.default.contents(atPath: path) else {
    throw BundleError.noContentsAtPath(path)
  }
  var presidents: T
  do {
    presidents = try JSONDecoder().decode(T.self, from: data)
  } catch {
    throw BundleError.decodingError(error)
  }
  return presidents
}
}

5. Unit test the Bundle extension for decoding the .json file

func testParseJSONFromBundle() {
  // arrange
  let bundle = Bundle.main
  let filename = "presidents"
  let firstBlackPresident = "Barack Obama"

  // act
  do {
    let presidents = try bundle.parseJSONFile(with: filename)
    // assert
    XCTAssertEqual(firstBlackPresident, presidents[43].name)
  } catch {
    XCTFail("bundle read error: \(error)")
  }
}

6. Populate the results in a Table View

class FeedViewController: UIViewController {
  enum Section {
    case main
  }
  
  typealias DataSource = UITableViewDiffableDataSource<Section, President>
  
  @IBOutlet weak var tableView: UITableView!
  private var dataSource: DataSource!
  
  override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(true)
    configureDataSource()
    fetchPresidents()
  }
  
  private func configureDataSource() {
    dataSource = DataSource(tableView: tableView, cellProvider: { (tableView, indexPath, president) -> UITableViewCell? in
      let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
      cell.textLabel?.text = president.name
      cell.detailTextLabel?.text = president.number.description
      return cell
    })
    dataSource.defaultRowAnimation = .fade
    
    var snapshot = NSDiffableDataSourceSnapshot<Section, President>()
    snapshot.appendSections([.main])
    dataSource.apply(snapshot, animatingDifferences: false)
  }
  
  private func fetchPresidents() {
    var presidents: [President]
    do {
      presidents = try Bundle.main.parseJSONFile(with: "presidents")
    } catch {
      fatalError("error: \(error)")
    }
    var snapshot = dataSource.snapshot()
    snapshot.appendItems(presidents, toSection: .main)
    dataSource.apply(snapshot, animatingDifferences: true)
  }

}

7. Table View