Asp.net MVC 4 异步方法

今天我们来看一下，同样功能在 Asp.net MVC 4 下的实现，基于.net framework 4.5 下的async支持，让我们的代码更加简单，看下面片断代码名叫Index的Action方法: 

        public async Task<ActionResult> IndexAsync()
        {
            var cnblogsTask = GetStringAsync("http://www.cnblogs.com");
            var myblogTask = GetStringAsync("http://www.cnblogs.com/wintersun");

            // Asynchronously wait for them all to complete.
            await Task.WhenAll(cnblogsTask, myblogTask);

            Operations translations = new Operations() {
                FirstOperation = cnblogsTask.Result, SecondOperation = myblogTask.Result };

            return View(translations);
        }
        private static async Task<string> GetStringAsync(string uri
            , CancellationToken cancelToken = default(CancellationToken))
        {
            using (HttpClient httpClient = new HttpClient())
            {
                var response = await httpClient.GetAsync(uri, cancelToken);
                return (await response.Content.ReadAsStringAsync());
            }
        }

上面的代码我们实现多个Task并行异步，注意async与await关键字，在.NET 4.5 与 Visual Studio 2012下可用。你只可以使用await关键字同时标注了async的方法。使用异法的HttpClient来替代WebClient类，await关键字运用到HttpClient的异步方法上。使用Task.WhenAll等待所有任务结束。我们知道TPL中还提供了CancellationToken，MVC框架中也提供了AsyncTimeout特性，看面下面示例代码: 

        [AsyncTimeout(100)]
        [HandleError(ExceptionType = typeof(TimeoutException),View = "Error")]
        public async Task<ActionResult> IndexCancleAsync()
        {
            var cancellationToken = new CancellationToken(false);
            var cnblogsTask = GetStringAsync("http://www.cnblogs.com", cancellationToken);
            var myblogTask = GetStringAsync("http://www.cnblogs.com/wintersun", cancellationToken);

            await Task.WhenAll(cnblogsTask, myblogTask);

            Operations translations = new Operations()
            {
                FirstOperation = cnblogsTask.Result,
                SecondOperation = myblogTask.Result
            };

            return View(translations);
        }

我们设置异步超时为100毫秒，并且我们可以传递CancellationToken的参数给具体的Task。 最后把结果返回给View，实际你可以自行Debug看其中过程。