How can I stop URLSessionTask when the Internet is disconnected? - ios

Question

I am using URLSessionTask to get the source code of url. When the internet is connected, it works well.
However, when the Internet is disconnected, I try building. And in simulator it is blank and the cpu is 0%. What affects is that My Tab Bar Controller is also missing and blank (It is my initial view controller). It seems that this task is under connecting?
I want the data received from dataTask, so I use semaphore to make it synchronous. Otherwise, as dataTask is an asynchronous action, what I
get is an empty string.
How can I fix this problem?
Thanks!
let urlString:String="http://www.career.fudan.edu.cn/jsp/career_talk_list.jsp?count=50&list=true"
let url = URL(string:urlString)
let request = URLRequest(url: url!)
let session = URLSession.shared
let semaphore = DispatchSemaphore(value: 0)
let dataTask = session.dataTask(with: request,
completionHandler: {(data, response, error) -> Void in
if error != nil{
errorString = "Error!"
}else{
htmlStr = String(data: data!, encoding: String.Encoding.utf8)!
//print(htmlStr)
}
semaphore.signal()
}) as URLSessionTask
//start task
dataTask.resume()
_ = semaphore.wait(timeout: DispatchTime.distantFuture)

Answer 1

Update: As #Moritz mentioned, I finally use completion handler (callback).
func getforData(completion: #escaping (String) -> ()) {
if let url = URL(string: "http://XXXXX") {
let request = URLRequest(url: url)
let task = URLSession.shared.dataTask(with: request) {
data, response, error in
if let data = data, let getString = String(data: data, encoding: String.Encoding.utf8), error == nil {
completion(getString)
} else {
print("error=\(error!.localizedDescription)")
}
}
task.resume()
}
}
And in viewdidload
override func viewDidLoad() {
super.viewDidLoad()
getforData { getString in
// and here we get the "returned" value from the asynchronous task
print(getString) //works well
//tableview should work in main thread
DispatchQueue.main.async {
self.newsTableView.dataSource = self
self.newsTableView.delegate = self
self.newsTableView.reloadData()
}
}