从 Swift 中的 URL 获取数据

Question

I'm trying to download JSON file from server & following an tutorial to do this ( http://www.learnswiftonline.com/mini-tutorials/how-to-download-and-read-json/ )

First I tried 'checking the response' part (I added some part to see what's wrong)

let requestURL: NSURL = NSURL(string: "http://www.learnswiftonline.com/Samples/subway.json")!
let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(urlRequest) {
    (data, response, error) -> Void in

        let httpResponse = response as! NSHTTPURLResponse
        let statusCode = httpResponse.statusCode

        if (statusCode == 200) {
            print("Everyone is fine, file downloaded successfully.")
        } else  {
            print("Failed")
        }

task.resume()

This should print either "Everyone is fine~" or "Failed" but neither comes up... I tried to see statusCode so I put print(statusCode) inside task but again nothing is printed.

This is my screenshot of the playground:

+

CFRunLoop in Swift Command Line Program

This was the answer I was looking for, since I was dealing with OS X command line application (I moved the whole bunch to playground to see what would happen). Check this if you're the same with me

Answer 1

You can not see anything because dataTaskWithRequest is asynchronous, and your playground just stops after 'task.resume()`. The asynchronous task does not get the change to run.

You can call this in the end, after task.resume :

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

also 'import XCPlayground', something like this:

import Foundation
import XCPlayground

let requestURL: NSURL = NSURL(string:  "http://www.learnswiftonline.com/Samples/subway.json")!
let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(urlRequest) {(data, response, error) -> Void in

  let httpResponse = response as! NSHTTPURLResponse
  let statusCode = httpResponse.statusCode

  if (statusCode == 200) {
     print("Everyone is fine, file downloaded successfully.")
  } else  {
     print("Failed")
  }

}
task.resume()

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

This post may clarify more: How do I run Asynchronous callbacks in Playground

EDIT:

In Swift 3, this changed a bit.

import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

Answer 2

works fine in my project after I changed "http" -> https, Apple announced “App Transport Security” for iOS 9 and OSX 10.11 El Capitan

    let requestURL: NSURL = NSURL(string: "https://www.learnswiftonline.com/Samples/subway.json")!
    let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
    let session = NSURLSession.sharedSession()
    let task = session.dataTaskWithRequest(urlRequest) {
        (data, response, error) -> Void in

        let httpResponse = response as! NSHTTPURLResponse
        let statusCode = httpResponse.statusCode

        if (statusCode == 200) {
            print("Everyone is fine, file downloaded successfully.")
        } else  {
            print("Failed")
        }
    }
        task.resume()

the http response:

 <NSHTTPURLResponse: 0x7a670300> { URL: https://www.learnswiftonline.com/Samples/subway.json } { status code: 200, headers {
"Content-Encoding" = gzip;
"Content-Type" = "application/json";
Date = "Tue, 16 Feb 2016 07:43:05 GMT";
"Last-Modified" = "Sat, 14 Nov 2015 08:21:26 GMT";
Server = "cloudflare-nginx";
"Set-Cookie" = "__cfduid=d9d92befe8746168b2b291f5bfb8996081455608585; expires=Wed, 15-Feb-17 07:43:05 GMT; path=/; domain=.learnswiftonline.com; HttpOnly";
"cf-ray" = "27579e989ad5208a-KIX";

} }

or error if use http

    Domain=NSURLErrorDomain Code=-1022 "The resource could not be loaded because the App Transport Security policy requires the use of a secure connection." UserInfo={NSErrorFailingURLStringKey=http://www.learnswiftonline.com/Samples/subway.json, NSErrorFailingURLKey=http://www.learnswiftonline.com/Samples/subway.json, NSLocalizedDescription=The resource could not be loaded because the App Transport Security policy requires the use of a secure connection., NSUnderlyingError=0x7866de20 {Error Domain=kCFErrorDomainCFNetwork Code=-1022 "(null)"}})

Answer 3

Swift 5

let requestURL: NSURL = NSURL(string: "https://irdirect.net/template_files/1294/stock-price.html")!
    let urlRequest: NSMutableURLRequest = NSMutableURLRequest(url: requestURL as URL)
    let session = URLSession.shared
    let task = session.dataTask(with: urlRequest as URLRequest) {
            (data, response, error) -> Void in

        let httpResponse = response as! HTTPURLResponse
            let statusCode = httpResponse.statusCode

            if (statusCode == 200) {
                print("Everyone is fine, file downloaded successfully.")
                do{
                     let json = try JSONSerialization.jsonObject(with: data!, options: []) as? [String : Any]
                 }
                 catch{ print("erroMsg") }

            } else  {
                print("Failed")
            }
        }
            task.resume()
}