Value of type 'System.Threading.Tasks.Task(Of String)' cannot be converted to 'String'

Question

I guess i am doing something terrible wrong here...

Dim s As String = GetResponse("", New KeyValuePair(Of String, String))

  Public Async Function GetResponse(ByVal url As String, ByVal params As KeyValuePair(Of String, String)) As System.Threading.Tasks.Task(Of String)
        Dim values = New List(Of KeyValuePair(Of String, String))
        Dim httpClient = New HttpClient(New HttpClientHandler())
        Dim response As HttpResponseMessage = Await httpClient.PostAsync(url, New FormUrlEncodedContent(values))
        response.EnsureSuccessStatusCode()
        Return Await response.Content.ReadAsStringAsync()
    End Function

any ideas please?

Dominic B. · Accepted Answer · 2014-04-16 19:05:49Z

4

Your function returs not a string. it returns a Task(Of String), like it says in the error message and as you can see in your function declaration. You see, it is not working as you think.

Solution should be: Try calling GetResponse("", New KeyValuePair(Of String, String)).Result, that will do what you want. The Result is the type like the type parameter of your Task.

edited Apr 16, 2014 at 19:05

answered Apr 16, 2014 at 18:31

Dominic B.

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Stephen Cleary · Accepted Answer · 2014-04-16 18:58:03Z

2

You should Await tasks to "unwrap" their result, as such:

Dim s As String = Await GetResponse("", New KeyValuePair(Of String, String))

Yes, this does mean that the calling method does need to be Async, so it's callers must use Await, etc. This is perfectly natural; Async does "infect" the code base like this.

answered Apr 16, 2014 at 18:58

Stephen Cleary

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