Threading exception when attempting to return String from async method

Question

I am working on a Winforms app that makes some HTTP based API calls to various web services within a Timer control loop. The web services are called using the async keyword. The problem is that I get a Threading exception when attempting to return the result as a string.

private async Task<String> UpdateViaApi(ClientInfoObject clientInfoObject)
{
    HttpResponseMessage response = await myHttpClient.SendAsync(request);
    string result = await response.Content.ReadAsStringAsync();
    return result;
}

Here is how I call the method ...

string result = UpdateViaApi(clientInfoObject);

The ClientInfoObject is a simple class that contains data as a series of properties. Am I using Task properly?

That won't even compile. UpdateViaApi returns a Task<string> not a string. — Mike Zboray
– Mike Zboray, Commented Jul 28, 2014 at 17:08

Stephen Cleary · Accepted Answer · 2014-07-28 17:08:04Z

4

You need to await the returned task:

string result = await UpdateViaApi(clientInfoObject);

Also, note that the method name should end in Async, to conform to the convention:

string result = await UpdateViaApiAsync(clientInfoObject);

answered Jul 28, 2014 at 17:08

Stephen Cleary

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3 Comments

webworm Over a year ago

Thanks for the response. When I add the keyword await I get the error

The await operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'.

Also, reading your book at the moment. Good information.

Servy Over a year ago

@webworm Now did you read the error message and follow the instructions that it gave you?

webworm Over a year ago

Indeed I did. Looks like the method that contained UpdateViaApiAsync(clientInfoObject) also need to be prefixed with the await operator.

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