Cannot make Task <HttpResponseMessage> "await"

Question

I am trying to write a method in my web api wrapper. I want to make use of "async/await" feature so that UI doesn't get blocked. Below is the code snippet in the web api wrapper.

 public static async Task Get<T>(Dictionary<string, string> paramDictionary, string controller) { try { string absoluteUrl = BaseUrl + controller + "?"; absoluteUrl = paramDictionary.Aggregate(absoluteUrl, (current, keyValuePair) => current + (keyValuePair.Key + "=" + keyValuePair.Value + "&")); absoluteUrl = absoluteUrl.TrimEnd('&'); using (HttpClient client = GetClient(absoluteUrl)) { HttpResponseMessage response = await client.GetAsync(absoluteUrl); return await response.Content.ReadAsAsync<T>(); } } catch (Exception exception) { throw exception; } }

The problem is I get compiler error at the statement below.

HttpResponseMessage response = await client.GetAsync(absoluteUrl);

It says "Type System.Threading.Tasks.Task <System.Net.Http.HttpResponseMessage> is not awaitable". After much searching I am not able to get rid of this error. Any ideas where I am going wrong? Please help.

side note: throw exception; will destroy the callstack. Just use throw; — jgauffin
– jgauffin, Commented Jun 2, 2014 at 11:10
I tried the code in the using block and the first line compiles, but the compiler didn't find the definition of ReadAsAsync<T>. Is that an extension method? — NeddySpaghetti
– NeddySpaghetti, Commented Jun 2, 2014 at 11:12
@jgauffin yeah an in addition to that it's not really necessary to catch an exception just for re-throwing it. just remove the whole try catch part here... — gsharp
– gsharp, Commented Jun 2, 2014 at 11:12
Are you targeting .Net 4.0 in VS2013? The version of Task in .Net 4.0 does not have the required GetAwaiter method so it cannot be used with async/await. You can use the async targeting pack to add the required methods. — Lee
– Lee, Commented Jun 2, 2014 at 11:32
@NedStoyanov, yep it does, same as as try/catch/finally and other C# control flow statements. Although, you cannot await inside catch/finally (you can inside try). — noseratio
– noseratio, Commented Jun 2, 2014 at 11:53

noseratio · Accepted Answer · 2014-06-02 11:28:37Z

5

As far as I can tell, it's because your method returns Task, not Task<T>. So you cannot do return await response.Content.ReadAsAsync<T>(). Change the signature to return Task<T>:

public static async Task<T> Get<T>(...)

answered Jun 2, 2014 at 11:28

noseratio

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12 Comments

Tejas Sutar Over a year ago

I tried your way. But didn't work unfortunately..:-(

noseratio Over a year ago

@TejasSutar, now that you've changed the signature to Task<T>, what's the error message and what line exactly gives it?

noseratio Over a year ago

@TejasSutar, are you indeed targeting Net 4.0?

Tejas Sutar Over a year ago

It's the same error message I mentioned earlier. One more thing I forgot to mention that compiler cannot find definition for ReadAsAsync method. I am referring following site for code: asp.net/web-api/overview/web-api-clients/…

Tejas Sutar Over a year ago

Yes. I just added Microsoft.Bcl.Async using package manager in VS. Now I need to get rid of compiler error at the statement "return await response.Content.ReadAsAsync<T>();" Thanks for help @Noseratio.

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Ryan Chu · Accepted Answer · 2015-05-26 06:27:37Z

Hmmm... I did the following to get it compile.

Add web api 2.2 for the system.net.http.formatting extension dll

enter image description here

Change the method signature from Task to Task<T>

Good luck!

TheNameHobbs · Accepted Answer · 2017-11-03 17:42:34Z

0

Updating the Microsoft.Bcl.Build Nuget package worked for me.

answered Nov 3, 2017 at 17:42

TheNameHobbs

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