Let’s go through each step with Swift code:

1. Get OpenWeatherMap API Key:
   • Go to the OpenWeatherMap website and sign up for an account to get your API key.
2. Create a New Xcode Project:
   • Open Xcode and create a new iOS project with a Single View App template.
3. UI Design:
   • Open the Main.storyboard file and design your user interface.
   • Add a label for displaying weather information and a text field for entering the location.
   • Add a button for fetching weather data and connect it to an IBAction in your view controller.
4. Networking:
   • Create a new Swift file named WeatherAPI.swift.

import Foundation

struct WeatherAPI {
    static let apiKey = "YOUR_API_KEY"
    static let baseURL = "http://api.openweathermap.org/data/2.5/weather"

    static func fetchWeatherData(for city: String, completion: @escaping (Result<WeatherData, Error>) -> Void) {
        let urlString = "\(baseURL)?q=\(city)&appid=\(apiKey)"
        guard let url = URL(string: urlString) else {
            completion(.failure(NSError(domain: "Invalid URL", code: 0, userInfo: nil)))
            return
        }

        URLSession.shared.dataTask(with: url) { data, response, error in
            if let error = error {
                completion(.failure(error))
                return
            }

            guard let data = data else {
                completion(.failure(NSError(domain: "No data received", code: 0, userInfo: nil)))
                return
            }

            do {
                let weatherData = try JSONDecoder().decode(WeatherData.self, from: data)
                completion(.success(weatherData))
            } catch {
                completion(.failure(error))
            }
        }.resume()
    }
}

5. Define Data Model:
   • Create a new Swift file named WeatherData.swift.

import Foundation

struct WeatherData: Codable {
    let main: Main
    let weather: [Weather]
}

struct Main: Codable {
    let temp: Double
}

struct Weather: Codable {
    let description: String
}

6. Update UI:
   • Open ViewController.swift and implement the IBAction for the fetch weather button.

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var locationTextField: UITextField!
    @IBOutlet weak var weatherLabel: UILabel!

    @IBAction func fetchWeatherButtonTapped(_ sender: UIButton) {
        guard let city = locationTextField.text else { return }
        
        WeatherAPI.fetchWeatherData(for: city) { result in
            switch result {
            case .success(let weatherData):
                let temperature = String(format: "%.1f", weatherData.main.temp - 273.15)
                let description = weatherData.weather.first?.description ?? ""
                DispatchQueue.main.async {
                    self.weatherLabel.text = "Temperature: \(temperature)°C, Description: \(description)"
                }
            case .failure(let error):
                DispatchQueue.main.async {
                    self.weatherLabel.text = "Error: \(error.localizedDescription)"
                }
            }
        }
    }
}

7. Error Handling:
   • The error handling is done within the fetchWeatherData method of WeatherAPI.swift.
8. Testing:
   • Run your app in the simulator or on a device and test it with different locations.
9. User Experience Enhancements:
   • You can add additional features like automatic location detection using Core Location or unit conversion.
10. Deployment:
    • Once your app is ready, you can deploy it to the App Store or distribute it to testers.

This code fetches weather data for a given city using the OpenWeatherMap API and displays the temperature and weather description in the UI. Make sure to replace “YOUR_API_KEY” with your actual OpenWeatherMap API key.