How to return a string from async

Question

My method is calling a web service and working asynchronusly.

When getting response, everything works fine and I am getting my response.

The problem starts when I need to return this response.

here is the code of my method:

 public async Task<string> sendWithHttpClient(string requestUrl, string json)
        {
            try
            {
                Uri requestUri = new Uri(requestUrl);
                using (var client = new HttpClient())
                {
                    client.DefaultRequestHeaders.Clear();
                    ...//adding things to header and creating requestcontent
                    var response = await client.PostAsync(requestUri, requestContent);

                    if (response.IsSuccessStatusCode)
                    {

                        Debug.WriteLine("Success");
                        HttpContent stream = response.Content;
                        //Task<string> data = stream.ReadAsStringAsync();    
                        var data = await stream.ReadAsStringAsync();
                        Debug.WriteLine("data len: " + data.Length);
                        Debug.WriteLine("data: " + data);
                        return data;                       
                    }
                    else
                    {
                        Debug.WriteLine("Unsuccessful!");
                        Debug.WriteLine("response.StatusCode: " + response.StatusCode);
                        Debug.WriteLine("response.ReasonPhrase: " + response.ReasonPhrase);
                        HttpContent stream = response.Content;    
                        var data = await stream.ReadAsStringAsync();
                        return data;
                     }
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine("ex: " + ex.Message);
                return null;
            }

and I am calling it this way:

      Task <string> result =  wsUtils.sendWithHttpClient(fullReq, "");           
      Debug.WriteLine("result:: " + result);

but when printing result I am seeing something like this: System.Threading.Tasks.Task

how can I get the result string as I did with data inside my method.

you need to access the Result property of your Task to get the desired output . — Amit Kumar Ghosh
– Amit Kumar Ghosh, Commented Jul 21, 2015 at 10:19

niico · Accepted Answer · 2017-01-31 16:05:29Z

34

You need to do this since you are calling the async method synchronously:

  Task<string> result =  wsUtils.sendWithHttpClient(fullReq, "");           
  Debug.WriteLine("result:: " + result.Result); // Call the Result

Think of the Task<string> return type as a 'promise' to return a value in the future.

If you called the async method asynchronously then it would be like the following:

  string result =  await wsUtils.sendWithHttpClient(fullReq, "");           
  Debug.WriteLine("result:: " + result);

edited Jan 31, 2017 at 16:05

niico

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answered Jul 21, 2015 at 10:08

Jamie Rees

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4 Comments

eeadev Over a year ago

I called it async, and it works, thanks. I will accept it soon.

Emile Over a year ago

The wait is not necessary. The Result property blocks the calling thread until the task finishes. See msdn.microsoft.com/en-us/library/dd537613(v=vs.110).aspx

Sharunas Bielskis Over a year ago

I used it succesfully.

danijeljw-RPC Over a year ago

As soon as I read the line "Think of the Task<string> return type as a 'promise' to return a value in the future." I instantly realised my mistake. The await` was missing. I'm going to mentally bookmark this statement. Thank you!

Stephen Cleary · Accepted Answer · 2015-07-21 12:08:51Z

10

An asynchronous method returns a task, representing a future value. In order to get the actual value wrapped in that task, you should await it:

string result = await wsUtils.sendWithHttpClient(fullReq, "");
Debug.WriteLine("result:: " + result);

Note that this will require your calling method to be asynchronous. This is both natural and correct.

answered Jul 21, 2015 at 12:08

Stephen Cleary

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