print barcode labels in c# Custom ActionResult Objects in VB.NET

Drawing Quick Response Code in VB.NET Custom ActionResult Objects

Ultimately, the action result object is a way to encapsulate all the tasks you need to accomplish in particular situations, such as when a requested resource is missing or redirected or when some special response must be served to the browser. Let s examine a few interesting scenarios for having custom action result objects.

In 8, we discussed permanent redirection as an aspect of a Web application that can have a nontrivial impact on Search Engine Optimization (SEO). Suppose that at some point you decide to expose a given feature of your application through another URL but

still need to support the old URL. To increase your SEO ratio, you might want to implement a permanent redirect instead of a classic (temporary) HTTP 302 redirect. ASP.NET MVC supplies a RedirectResult class, but it lacks a PermanentRedirectResult class. Here s a possible implementation that follows closely that of RedirectResult in ASP.NET MVC 2:

public class PermanentRedirectResult : ActionResult { public string Url { get; set; } public bool ShouldEndResponse { get; set; } public PermanentRedirectResult(string url) { if (String.IsNullOrEmpty(url)) throw new ArgumentException("url"); Url = url; ShouldEndResponse = false; } public override void ExecuteResult(ControllerContext context) { // Preconditions if (context == null) throw new ArgumentNullException("context"); if (context.IsChildAction) throw new InvalidOperationException(); // Mark all keys in the TempData dictionary for retention context.Controller.TempData.Keep(); // Prepare the response string url = UrlHelper.GenerateContentUrl(Url, context.HttpContext); HttpResponseBase response = context.HttpContext.Response; response.Clear(); response.StatusCode = 301; response.AddHeader("Location", url); // Optionally end the request if (ShouldEndResponse) response.End(); } }

By having this class available, you can easily move your features around without affecting the SEO level of your application:

public ActionResult Old() { string newUrl = "/Home/Index"; return new PermanentRedirectResult(newUrl); }

If you search the Web for a nontrivial example of an action result, you likely find a syndication action result object at the top of the list. Let s briefly go through this popular example. The class SyndicationResult supports both RSS 2.0 and ATOM 1.0 and offers a handy property for you to choose programmatically. By default, the class produces an RSS 2.0 feed. To compile this example, you need to reference the System.ServiceModel.Web assembly and import the System.ServiceModel.Syndication namespace:

public class SyndicationResult : ActionResult { public SyndicationFeed Feed { get; set; } public FeedType Type { get; set; } public SyndicationResult() { Type = FeedType.Rss; }

public SyndicationResult( string title, string description, Uri uri, IEnumerable<SyndicationItem> items) { Type = FeedType.Rss; Feed = new SyndicationFeed(title, description, uri, items); } public SyndicationResult(SyndicationFeed feed) { Type = FeedType.Rss; Feed = feed; } public override void ExecuteResult(ControllerContext context) { // Set the content type context.HttpContext.Response.ContentType = GetContentType(); // Create the feed and write it to the output stream var feedFormatter = GetFeedFormatter(); var writer = XmlWriter.Create(context.HttpContext.Response.Output); if (writer == null) return; feedFormatter.WriteTo(writer); writer.Close(); } private string GetContentType() { if(Type == FeedType.Atom) return "application/atom+xml"; return "application/rss+xml"; } private SyndicationFeedFormatter GetFeedFormatter() { if (Type == FeedType.Atom) return new Atom10FeedFormatter(Feed); return new Rss20FeedFormatter(Feed); } } public enum FeedType { Rss = 0, Atom = 1 }

The class gets a syndication feed and just serializes it to the client using either the RSS 2.0 or ATOM 1.0 format. Creating a consumable feed is another story; but it is also a concern that belongs to the controller rather than to the infrastructure. Here s how to write a controller method that returns a feed:

public SyndicationResult Blog() { var items = new List<SyndicationItem>(); items.Add(new SyndicationItem( "Controller descriptors",

"This post shows how to customize controller descriptors", null)); items.Add(new SyndicationItem( "Action filters", "Using a fluent API to define action filters", null)); items.Add(new SyndicationItem( "Custom action results", "Create a custom action result for syndication data", null)); var result = new SyndicationResult( "Programming ASP.NET MVC 2", "Dino's latest book", Request.Url, items); result.Type = FeedType.Atom; return result; }

You create a list of SyndicationItem objects and provide for each a title, some content, and an alternate link (null in the code snippet). You typically retrieve these items from some repository you might have in your application. Finally, you pass items to the SyndicationResult object along with a title and description for the feed to be created and serialized. Figure 11-6 shows an ATOM feed in Internet Explorer.