/// 

/// 異步方法
/// 
/// 
public  Task Index()
{
    return Task.Run(() => {
        using (StreamReader sr = new StreamReader("F:\test.txt"))
        {
            string txt = sr.ReadToEnd();
            return Content(txt);
        }
    });
}

/// 

/// 異步方法，并使用async標(biāo)注
/// 
/// 
public async Task Index()
{
    using (StreamReader sr = new StreamReader("F:\test.txt"))
    {
        string txt =await sr.ReadToEndAsync();
        return Content(txt);
    }
        //return View();
}