我是一个初学Swift编码的人，正在尝试从NewsAPI网站解析JSON数据并使用它。 我已经成功地解析了JSON数据，并且它是通过结构来组织的，但是我无法将它设置为后台线程之外的变量，也无法在后台线程之外使用它。 有什么建议吗？ 我已经包含了我的代码。
谢谢
import UIKit
class ViewController: UIViewController {
var test:Int?
override func viewDidLoad() {
super.viewDidLoad()
GrabJSON()
}
@IBOutlet weak var labelTime: UILabel!
func GrabJSON() {
// hit the API endpoint
let urlString = "http://newsapi.org/v2/everything?q=bitcoin&from=2020-05-13&sortBy=publishedAt&apiKey=_________(it actually is here)"
let url = URL(string: urlString)
guard url != nil else {
return
}
let session = URLSession.shared
let dataTask = session.dataTask(with: url!) { (data, response, error) in
// check for errors
if error == nil && data != nil {
// if there is no error and there is data
let decoder = JSONDecoder()
do {
//parse json
let newsFeed = try decoder.decode(NewsFeed.self, from: data!)
print(newsFeed)
}
catch {
print("error in JSON parsing")
}
}
}
// makes the API call
dataTask.resume()
}
}
由于session.dataTask()是异步的（您向它传递一个回调），因此您可以类似地在GrabJSON函数中提供一个回调参数，如下所示:
func GrabJSON(callback: NewsFeed -> Void) {
// hit the API endpoint
let urlString = "http://newsapi.org/v2/everything?q=bitcoin&from=2020-05-13&sortBy=publishedAt&apiKey=_________(it actually is here)"
let url = URL(string: urlString)
guard url != nil else {
return
}
let session = URLSession.shared
let dataTask = session.dataTask(with: url!) { (data, response, error) in
// check for errors
if error == nil && data != nil {
// if there is no error and there is data
let decoder = JSONDecoder()
do {
//parse json
let newsFeed = try decoder.decode(NewsFeed.self, from: data!)
print(newsFeed)
callback(newsFeed) // call the callback
}
catch {
print("error in JSON parsing")
}
}
// makes the API call
dataTask.resume()
}
那么在其他地方，您可以像这样使用它:
GrabJson { newsFeed in
// do stuff with newsFeed json
}
