API (Application Programming Interface) is a set of commands, function, protocols, objects that programmers can use to create software or interact with an external system.

1. 공식 문서를 통해서 가입하고 확인할 것.

• list of condition code
  • https://openweathermap.org/current#list
  • https://openweathermap.org/weather-conditions

How to networking with Web Server?

<aside> 💡 내 앱과 웹서버와의 통신 (request, response)을 어떻게 할까?

</aside>

four steps to networking

1. Create a URL
   1. use URL(string: string)
2. Create a URLSession
3. Give URLSession a task
4. Start the task

func performRequest(urlString: String) {
    //1. create a url
    if let url = URL(string: urlString) {
        //2. creata a url session
        let session = URLSession(configuration: .default)
        //3. give the session a task
        let task =  session.dataTask(with: url, completionHandler: handle(data:response:error:))
        //handler는 비동기처리를 위한 함수.
        //4. start the task
        print("start the task")
        task.resume()
    }
}

func handle(data: Data?, response: URLResponse?, error: Error?) -> Void {
    if error != nil {
        print(error!)
        return
    }
    print("비동기처리 핸들러 데이터가 오기전까지 실행안됨")
    
    if let safeData = data {
        let dataString = String(data: safeData, encoding: .utf8)
        print(dataString)
    }
}

URLSession

https://developer.apple.com/documentation/foundation/urlsession

JSON parsing

JSON (JavaScript Object Notation)

we initialize swift object with either a struct or a class