Getting return value from Task.Run

Question

I have the following code here

    public static async Task<string> Start(IProgress<ProcessTaskAsyncExProgress> progress)
    {
        const int total = 10;
        for (var i = 0; i <= total; i++)
        {
            await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));
            if (progress != null)
            {
                var args = new ProcessTaskAsyncExProgress
                {
                    ProgressPercentage = (int)(i / (double)total * 100.0),
                    Text = "processing " + i
                };
                progress.Report(args);
            }
        }
        return "Done";
    }

    private static string RunLongTask(string taskName)
    {
        Task.Delay(300);
        return taskName + "Completed!";
    }

In this line:

await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));

How do I get back the string value of RunLongTask?

I've tried

var val = await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture))).Result;

But I get an error "string is not awaitable"

Answer 1

This is not a direct answer to old question, but for others searching:

"Normally" you shouldn't do this, but sometimes you need to match a library API so you can use a wrapper function like below:

private async Task<string> WrapSomeMethod(string someParam)
{
    //adding .ConfigureAwait(false) may NOT be what you want but google it.
    return await Task.Run(() => SomeObj.SomeMethodAsync(someParam)).ConfigureAwait(false);
}

And then call that instead with .Result like below:

string blah = WrapSomeMethod(someParam).Result;

Answer 2

Remove the Result from the end. When you await you will get the Result back from the await-able method.

var val = await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));