How to dynamically generate sitemap xml for an asp.net mvc website?

The simplest way I found on web to generate such dynamic sitemap using mvc asp.net(c#) is following a three steps procedure in which we just need to create two classes and a controller method.
Step 1 – Create A CustomSitemapItem Class
The CustomSitemapItem Class will be used to store all the properties we need for each sitemap URL entry.

public class CustomSitemapItem {
    public DateTime? DateAdded { get; set; }
    public string URL { get; set; }
    public string Priority { get; set; }
}

Step 2 – Create A CustomSitemapActionResult

public class CustomSitemapActionResult : ActionResult
    {
        private List<CustomSitemapItem> _SitemapItems;
        private string _Website;
        public CustomSitemapActionResult(List<CustomSitemapItem> SitemapItems, string Website)
        {
            this._SitemapItems = SitemapItems;
            this._Website = Website;
        }
        public override void ExecuteResult(ControllerContext context)
        {
            context.HttpContext.Response.ContentType = "text/xml";
            using (XmlWriter writer = XmlWriter.Create(context.HttpContext.Response.Output))
            {
                writer.WriteStartElement("urlset", "http://www.sitemaps.org/schemas/sitemap/0.9");
                foreach (var SiteMapItem in this._SitemapItems)
                {
                    writer.WriteStartElement("url");
                    writer.WriteElementString("loc", string.Format(this._Website + "{0}", SiteMapItem.URL));
                    if (SiteMapItem.DateAdded != null)
                    {
                        writer.WriteElementString("lastmod", string.Format("{0:yyyy-MM-dd}", SiteMapItem.DateAdded));
                    }
                    writer.WriteElementString("changefreq", "daily");
                    writer.WriteElementString("priority", SiteMapItem.Priority);
                    writer.WriteEndElement();
                }
                writer.WriteEndElement();
                writer.Flush();
                writer.Close();
            }
        }
    }

The CustomSitemapActionResult is the result that comes back from the controller when the URL /sitemap is called. It takes a list of CustomSitemapItem classes and generates the corresponding xml file that will be used by different search engines to index your website.
Step 3 – Create A Sitemap Controller Method
The controller is where you will generate your list of CustomSitemapItem classes that will be returned via the CustomSitemapActionResult

       [OutputCache(Duration = 120, VaryByParam = "none")]
        public CustomSitemapActionResult Sitemap()
        {
            var Website = "http://www.mysitedomain.com";
            var currentdate = DateTime.Now;
            var SitemapItems = new List<CustomSitemapItem>();
            //Static items will be added as follows
            SitemapItems.Add(new CustomSitemapItem
            {
                URL = "",
                Priority = "1",
                DateAdded = currentdate
            });
            SitemapItems.Add(new CustomSitemapItem
            {
                URL = "/about",
                Priority = ".9",
                DateAdded = currentdate
            });
            SitemapItems.Add(new CustomSitemapItem
            {
                URL = "/contact",
                Priority = ".9",
                DateAdded = currentdate
            });
            SitemapItems.Add(new CustomSitemapItem
            {
                URL = "/terms-and-condition",
                Priority = ".9",
                DateAdded = currentdate
            });
            
            //Dynamic items will be added as follows
            var allNews = News.GetWithAllStatus().Where(t => t.Status == Status.Active);
            foreach (var item in allNews)
            {
                int totalCount = 0;
                SitemapItems.Add(new CustomSitemapItem
                {
                    URL = "/News/" + item.UrlName,
                    Priority = ".8",
                    DateAdded = item.DateCreated
                });
            }
            //Dynamic items will be added as follows
            var allBlogPosts = BlogPosts.GetWithAllStatus().Where(p => p.Status == Status.Active);
            foreach (var item in allBlogPosts)
            {
                SitemapItems.Add(new CustomSitemapItem
                {
                    URL = "/Blogpost/" + item.UrlName,
                    Priority = ".8",
                    DateAdded =item.DateCreated
                });
            }
            return new CustomSitemapActionResult(SitemapItems, Website);
        }

That’s it now you can simply use the controller method Sitemap() to get your sitemap xml.