Developer forum

    using System.Collections.Specialized;
    using System.Globalization;
    using System.Linq;
    using System.Web;

    using Dynamicweb;
    using Dynamicweb.eCommerce.Products;
    using Dynamicweb.Rendering;

    /// <summary>
    /// Renders links to previous and next product in the same group as the current product.
    /// </summary>
    public class PreviousNextProduct : ProductTemplateExtender
    {
        #region Constants and Fields

        private const string LinkDefault = "Default.aspx?";

        private const string LinkQueryPattern = "{0}={1}";

        private const string LinkQuerySeparator = "&";

        private const string TagPattern = "X:Product.{0}.{1}";

        private const string TagPrefixNextProduct = "NextProduct";

        private const string TagPrefixPreviousProduct = "PreviousProduct";

        #endregion

        #region Public Methods and Operators

        public override void ExtendTemplate(Template template)
        {
            var productId = Base.Request(ParameterName.ProductId);
            if (!this.Product.ID.Equals(productId))
            {
                // Do not proceed if this is not the details view of the current product. No need to render this on product lists.
                return;
            }

            // Get the group id from query string - make sure you use links including the group id (Ecom:Product.LinkGroup) on product lists.
            var groupId = Input.Request(ParameterName.GroupId);

            if (string.IsNullOrWhiteSpace(groupId))
            {
                // No group id was found, so we can't find the previous and next products.
                return;
            }

            // Get all products in the same group.
            var products = Product.GetProductsByGroupID(groupId);

            // Find the index of the current product and check if there are any previous and next products.
            var currentIndex = products.IndexOf(this.Product.ID);
            var hasPrevious = currentIndex > 0;
            var hasNext = currentIndex + 1 < products.Count;

            // Render the previous product if there is any.
            if (hasPrevious)
            {
                var previousProduct = products[currentIndex - 1];
                RenderProduct(template, TagPrefixPreviousProduct, previousProduct);
            }

            // Render the next product if there is any.
            if (hasNext)
            {
                var nextProduct = products[currentIndex + 1];
                RenderProduct(template, TagPrefixNextProduct, nextProduct);
            }
        }

        #endregion

        #region Methods

        private static string GenerateProductLink(Product product)
        {
            var query = new NameValueCollection(HttpContext.Current.Request.QueryString);
            query.Set(ParameterName.ProductId, product.ID);
            query.Set(ParameterName.VariantId, product.VariantID);

            var queryStringKeyValuePairs = from key in query.AllKeys 
                                           where !string.IsNullOrWhiteSpace(query[key])
                                           select string.Format(CultureInfo.InvariantCulture, LinkQueryPattern, key, query[key]);

            var queryString = string.Join(LinkQuerySeparator, queryStringKeyValuePairs);

            return LinkDefault + queryString;
        }

        private static void RenderProduct(Template template, string prefix, Product product)
        {
            var link = GenerateProductLink(product);
            template.SetTag(string.Format(CultureInfo.InvariantCulture, TagPattern, prefix, TagName.Id), product.ID);
            template.SetTag(string.Format(CultureInfo.InvariantCulture, TagPattern, prefix, TagName.VariantId), product.VariantID);
            template.SetTag(string.Format(CultureInfo.InvariantCulture, TagPattern, prefix, TagName.Name), product.Name);
            template.SetTag(string.Format(CultureInfo.InvariantCulture, TagPattern, prefix, TagName.Number), product.Number);
            template.SetTag(string.Format(CultureInfo.InvariantCulture, TagPattern, prefix, TagName.Link), link);
        }

        #endregion

        private static class ParameterName
        {
            #region Constants and Fields

            public const string GroupId = "GroupID";

            public const string ProductId = "ProductID";

            public const string VariantId = "VariantID";

            #endregion
        }

        private static class TagName
        {
            #region Constants and Fields

            public const string Id = "ID";

            public const string Link = "Link";

            public const string Name = "Name";

            public const string Number = "Number";

            public const string VariantId = "VariantID";

            #endregion
        }
    }