Swift-如何在完成函数之前播放URLSession？

Question

I am currently using a URLSession to send and receive data from a web server, but I have the problem that the query is executed at the end of any other code that follows it, for example if I have the following instructions:

_ = URLSession.shared.dataTask (with: url_request) 
{(data, response, error) in
}.resume ()

print ("Hello world")

First you will run the "Hello world" and then the http query, how can I make the URLSession run and then what is left of the code?

Answer 1

URL sessions are asynchronous and involve time in communicating back and forth to a server. You have to use a variant of the URLSession that allows you to have a completion handler:

    URLSession.shared.dataTask(with: my_url) { (response_data, url_response, communication_error) in
        print ("Hello World")
    }

Good luck!

Answer 2

This is the solution I found:

let semaphore = DispatchSemaphore(value: 0)

_ = URLSession.shared.dataTask (with: url_request) 
{(data, response, error) in
   print("One")
   semaphore.signal()
}.resume ()

_ = semaphore.wait(timeout: DispatchTime.distantFuture)
print (“Two”)

And this is what prints:

>> One
>> Two