12 ChAPTER 1 Design the application architecture LISTING 1-1 Calling an external data feed public async Task List() { ViewBag.SyncOrAsync = "Asynchronous"; string results = string.Empty; using (HttpClient httpClient = new HttpClient() { var response = await httpClient.GetAsync(new Uri("http://externalfeedsite")); Byte[] downloadedBytes = await response.Content.ReadAsByteArrayAsync(); Encoding encoding = new ASCIIEncoding(); results = encoding.GetString(downloadedBytes); } return PartialView("partialViewName", results); Asynchronous programming gives you different ways to solve performance issues where multithreading might help. You can create an action that returns synchronously but uses asynchronous work within the method to get work done faster. (The main thread has to wait only for the longest-running work unit to respond rather than waiting for all the work to occur, one after the other.) This kind of approach makes sense if you are merging the results from multiple service calls into a single model to be passed to the view. Another approach is to use an asynchronous partial view, such as in Listing 1-1. This helps the overall performance of your application by running the work in that partial view in a different thread, enabling the primary thread to continue to process other items. It also helps you avoid thread locking because your MVC4 application parses the action. A third approach is to break content out on the page and load it asynchronously from the client. A typical use case is to create your page normally, but rather than directly calling the action result @Html.Partial(“LeadArticleControl”, Model.LeadArticle) in your .cshtml file, you instead use JavaScript code that calls the server to ask for the partial view result after the page has been rendered on the client side, a traditional AJAX approach.