public class HomeController : Controller{[HttpGet]public ActionResult Index(){var model = new PlanModel() {};return View(model);}public ActionResult CaseRow(){return View("_CaseRow", new CaseModel());}[HttpPost]public ActionResult Form(PlanModel model){return Json(model);}}
public static class HtmlPrefixScopeExtensions{private const string IdsToReuseKey = "__htmlPrefixScopeExtensions_IdsToReuse_";public static IDisposable BeginCollectionItem(this IHtmlHelper html, string collectionName){return BeginCollectionItem(html, collectionName, html.ViewContext.Writer);}private static IDisposable BeginCollectionItem(this IHtmlHelper html, string collectionName, TextWriter writer){if (html.ViewData["ContainerPrefix"] != null)collectionName = string.Concat(html.ViewData["ContainerPrefix"], ".", collectionName);var idsToReuse = GetIdsToReuse(html.ViewContext.HttpContext, collectionName);var itemIndex = idsToReuse.Count > 0 ? idsToReuse.Dequeue() : Guid.NewGuid().ToString();string htmlFieldPrefix = $"{collectionName}[{itemIndex}]";html.ViewData["ContainerPrefix"] = htmlFieldPrefix;/* * html.Name(); has been removed* because of incorrect naming of collection items* e.g.* let collectionName = "Collection"* the first item's name was Collection[0].Collection[<GUID>]* instead of Collection[<GUID>]*/string indexInputName = $"{collectionName}.index";// autocomplete="off" is needed to work around a very annoying Chrome behaviour// whereby it reuses old values after the user clicks "Back", which causes the// xyz.index and xyz[...] values to get out of sync.writer.WriteLine($@"<input type=""hidden"" name=""{indexInputName}"" autocomplete=""off"" value=""{html.Encode(itemIndex)}"" />");return BeginHtmlFieldPrefixScope(html, htmlFieldPrefix);}private static IDisposable BeginHtmlFieldPrefixScope(this IHtmlHelper html, string htmlFieldPrefix){return new HtmlFieldPrefixScope(html.ViewData.TemplateInfo, htmlFieldPrefix);}private static Queue<string> GetIdsToReuse(HttpContext httpContext, string collectionName){// We need to use the same sequence of IDs following a server-side validation failure,// otherwise the framework won't render the validation error messages next to each item.var key = IdsToReuseKey + collectionName;var queue = (Queue<string>)httpContext.Items[key];if (queue == null){httpContext.Items[key] = queue = new Queue<string>();if (httpContext.Request.Method == "POST" && httpContext.Request.HasFormContentType){StringValues previouslyUsedIds = httpContext.Request.Form[collectionName + ".index"];if (!string.IsNullOrEmpty(previouslyUsedIds))foreach (var previouslyUsedId in previouslyUsedIds)queue.Enqueue(previouslyUsedId);}}return queue;}internal class HtmlFieldPrefixScope : IDisposable{internal readonly TemplateInfo TemplateInfo;internal readonly string PreviousHtmlFieldPrefix;public HtmlFieldPrefixScope(TemplateInfo templateInfo, string htmlFieldPrefix){TemplateInfo = templateInfo;PreviousHtmlFieldPrefix = TemplateInfo.HtmlFieldPrefix;TemplateInfo.HtmlFieldPrefix = htmlFieldPrefix;}public void Dispose(){TemplateInfo.HtmlFieldPrefix = PreviousHtmlFieldPrefix;}}}
