本篇实践在ASP.NET MVC 4下使用Session来保持表单的状态。

如上，输入俱乐部名称，点击"添加球员"，输入球员名称。我们希望，点击"到别的地方转转"跳转到另外一个视图页，当再次返回的时候能保持表单的状态。

点击"到别的地方转转"跳转到另外一个视图页如下：

再次返回，表单的状态被保持了：

点击"提交"按钮，显示表单的内容：

关于球员，对应的Model为：

复制
using System.ComponentModel.DataAnnotations;
namespace MvcApplication1.Models
{
    public class Player
    {
        public int Id { get; set; }
        [Required(ErrorMessage = "必填")]
        [Display(Name = "球员名称")]
        public string Name { get; set; }
    }
}

关于俱乐部，对应的Model为：

复制
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
namespace MvcApplication1.Models
{
    public class Club
    {
        public Club()
        {
            this.Players = new List<Player>();
        }
        public int Id { get; set; }
        [Required(ErrorMessage = "必填")]
        [Display(Name = "俱乐部名称")]
        public string Name { get; set; }
        public List<Player> Players { get; set; }
    }
}

在Home/Index.cshtml强类型视图中，

复制
@model MvcApplication1.Models.Club
@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
<h2>Index</h2>
@using (Html.BeginForm("Index", "Home", FormMethod.Post, new {id = "myForm"}))
{
    @Html.LabelFor(m => m.Name)
    @Html.TextBoxFor(m => m.Name)
    @Html.ValidationMessageFor(m => m.Name)
    <br/><br/>
    
    <ul id="players" style="list-style-type: none">
        @if (Model.Players != null)
        {
            foreach (var item in Model.Players)
            {
                Html.RenderAction("NewPlayerRow", "Home", new { player = @item });
            }
            
        }
    </ul>
    <a id="addPlayer" href="javascript:void(0)" rel="external nofollow"  rel="external nofollow" >添加球员</a>
    
    <br/><br/>
    
    <div>
        <a href="javascript:void(0)" rel="external nofollow"  rel="external nofollow"   id="gotoOther">到别的地方转转</a> &nbsp;
        <input type="submit" id="up" value="提交" />
    </div>
}
@section scripts
{
    <script src="~/Scripts/dynamicvalidation.js"></script>
    <script type="text/javascript">
        $(function () {
            //添加关于Player的新行
            $('#addPlayer').on("click", function() {
                createPlayerRow();
            });
            //到别的页
            $('#gotoOther').on("click", function() {
                if ($('#myForm').valid()) {
                    $.ajax({
                        cache: false,
                        url: '@Url.Action("BeforeGoToMustSave", "Home")',
                        type: 'POST',
                        dataType: 'json',
                        data: $('#myForm').serialize(),
                        success: function (data) {
                            if (data.msg) {
                                window.location.href = '@Url.Action("RealGoTo", "Home")';
                            }
                        },
                        error: function (xhr, status) {
                            alert("添加失败，状态码：" + status);
                        }
                    });
                }
            });
        });
        //添加品牌行
        function createPlayerRow() {
            $.ajax({
                cache: false,
                url: '@Url.Action("NewPlayerRow", "Home")',
                type: "GET",
                data: {},
                success: function (data) {
                    $('#players').append(data);
                    $.validator.unobtrusive.parseDynamicContent('#players li:last', "#myForm");
                },
                error: function (xhr, status) {
                    alert("添加行失败，状态码：" + status);
                }
            });
        }
    </script>
}

以上，

• 点击"添加球员"，向控制器发出异步请求，把部分视图li动态加载到ul中
• 点击"到别的地方转转",向控制器发出异步请求，正是在这时候，在控制器的Action中，实施把表单的状态保存到Session中
• 点击"提交"按钮，把表单信息显示出来

另外，当在页面上点击"添加球员"，为了让动态的部分视图能被验证，需要引入dynamicvalidation.js，调用其$.validator.unobtrusive.parseDynamicContent('#players li:last', "#myForm")方法，dynamicvalidation.js具体如下：

复制
//对动态生成内容客户端验证
(function ($) {
    $.validator.unobtrusive.parseDynamicContent = function (selector, formSelector) {
        $.validator.unobtrusive.parse(selector);
        var form = $(formSelector);
        var unobtrusiveValidation = form.data('unobtrusiveValidation');
        var validator = form.validate();
        $.each(unobtrusiveValidation.options.rules, function (elname, elrules) {
            if (validator.settings.rules[elname] == undefined) {
                var args = {};
                $.extend(args, elrules);
                args.messages = unobtrusiveValidation.options.messages[elname];
                //edit:use quoted strings for the name selector
                $("[name='" + elname + "']").rules("add", args);
            } else {
                $.each(elrules, function (rulename, data) {
                    if (validator.settings.rules[elname][rulename] == undefined) {
                        var args = {};
                        args[rulename] = data;
                        args.messages = unobtrusiveValidation.options.messages[elname][rulename];
                        //edit:use quoted strings for the name selector
                        $("[name='" + elname + "']").rules("add", args);
                    }
                });
            }
        });
    };
})(jQuery);

在HomeController中，

复制
   public class HomeController : Controller
    {
        private const string sessionKey = "myFormKey";
        public ActionResult Index()
        {
            Club club = null;
            if (Session[sessionKey] != null)
            {
                club = (Club) Session[sessionKey];
            }
            else
            {
                club = new Club();
            }
            return View(club);
        }
        //提交表单
        [HttpPost]
        public ActionResult Index(Club club)
        {
            if (ModelState.IsValid)
            {
                StringBuilder sb = new StringBuilder();
                sb.Append(club.Name);
                if (club.Players != null && club.Players.Count > 0)
                {
                    foreach (var item in club.Players)
                    {
                        sb.AppendFormat("--{0}", item.Name);
                    }
                }
                //删除Session
                //Session.Abandon();
                //Session.Clear();
                Session.Remove(sessionKey);
                return Content(sb.ToString());
            }
            else
            {
                return View(club);
            }
        }
        //添加新行
        public ActionResult NewPlayerRow(Player player)
        {
            return PartialView("_NewPlayer", player ?? new Player());
        }
        //跳转之前把表单保存到Session中
        [HttpPost]
        public ActionResult BeforeGoToMustSave(Club club)
        {
            Session[sessionKey] = club;
            return Json(new { msg = true });
        }
        //保存完Club的Session后真正跳转到的页面
        public ActionResult RealGoTo()
        {
            return View();
        }
    }

以上，

• 对于接收[HttpGet]请求的Index方法对应的视图，Session存在就从Session中取出Club实例，否则就创建一个空的club实例
• 对于接收[HttpPost]请求的Index方法对应的视图，显示表单内容之前把对应的Session删除
• 添加新行NewPlayerRow方法供显示或添加用，当Player类型参数为null的时候，实际就是点击"添加球员"显示新行
• BeforeGoToMustSave方法实际是为了在跳转之前保存Session
• RealGoTo是点击"到别的地方转转"后真正跳转的视图页

另外，所有视图页的公共页Layout.cshtml，必须引用异步验证的js。

复制
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
    @Styles.Render("~/Content/css")
    @Scripts.Render("~/bundles/jquery")
    @Scripts.Render("~/bundles/jqueryval")
</head>
<body>
    @RenderBody()
    
    @RenderSection("scripts", required: false)
</body>

Home/_NewPlayer.cshtml部分视图，是在点击"添加球员"之后动态加载的部分视图。

复制
@using MvcApplication1.Extension
@model MvcApplication1.Models.Player
<li  class="newcarcolorli">
     @using (Html.BeginCollectionItem("Players")) 
     {
        @Html.HiddenFor(model => model.Id)
         <div>
             @Html.LabelFor(m => m.Name)
             @Html.TextBoxFor(m => m.Name)
             @Html.ValidationMessageFor(m => m.Name)
         </div>  
     }
</li>

其中，用到了扩展Extension文件夹下CollectionEditingHtmlExtensions类的扩展方法，如下：

复制
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Mvc;
namespace MvcApplication1.Extension
{
    public static class CollectionEditingHtmlExtensions
    {
        //目标生成如下格式
        //<input autocomplete="off" name="FavouriteMovies.Index" type="hidden" value="6d85a95b-1dee-4175-bfae-73fad6a3763b" />
        //<label>Title</label>
        //<input class="text-box single-line" name="FavouriteMovies[6d85a95b-1dee-4175-bfae-73fad6a3763b].Title" type="text" value="Movie 1" />
        //<span class="field-validation-valid"></span>
        public static IDisposable BeginCollectionItem<TModel>(this HtmlHelper<TModel> html, string collectionName)
        {
            //构建name="FavouriteMovies.Index"
            string collectionIndexFieldName = string.Format("{0}.Index", collectionName);
            //构建Guid字符串
            string itemIndex = GetCollectionItemIndex(collectionIndexFieldName);
            //构建带上集合属性+Guid字符串的前缀
            string collectionItemName = string.Format("{0}[{1}]", collectionName, itemIndex);
            TagBuilder indexField = new TagBuilder("input");
            indexField.MergeAttributes(new Dictionary<string, string>()
            {
                {"name", string.Format("{0}.Index", collectionName)},
                {"value", itemIndex},
                {"type", "hidden"},
                {"autocomplete", "off"}
            });
            html.ViewContext.Writer.WriteLine(indexField.ToString(TagRenderMode.SelfClosing));
            return new CollectionItemNamePrefixScope(html.ViewData.TemplateInfo, collectionItemName);
        }
        private class CollectionItemNamePrefixScope : IDisposable
        {
            private readonly TemplateInfo _templateInfo;
            private readonly string _previousPrfix;
            //通过构造函数，先把TemplateInfo以及TemplateInfo.HtmlFieldPrefix赋值给私有字段变量，并把集合属性名称赋值给TemplateInfo.HtmlFieldPrefix
            public CollectionItemNamePrefixScope(TemplateInfo templateInfo, string collectionItemName)
            {
                this._templateInfo = templateInfo;
                this._previousPrfix = templateInfo.HtmlFieldPrefix;
                templateInfo.HtmlFieldPrefix = collectionItemName;
            }
            public void Dispose()
            {
                _templateInfo.HtmlFieldPrefix = _previousPrfix;
            }
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="collectionIndexFieldName">比如，FavouriteMovies.Index</param>
        /// <returns>Guid字符串</returns>
        private static string GetCollectionItemIndex(string collectionIndexFieldName)
        {
            Queue<string> previousIndices = (Queue<string>)HttpContext.Current.Items[collectionIndexFieldName];
            if (previousIndices == null)
            {
                HttpContext.Current.Items[collectionIndexFieldName] = previousIndices = new Queue<string>();
                string previousIndicesValues = HttpContext.Current.Request[collectionIndexFieldName];
                if (!string.IsNullOrWhiteSpace(previousIndicesValues))
                {
                    foreach (string index in previousIndicesValues.Split(','))
                    {
                        previousIndices.Enqueue(index);
                    }
                }
            }
            return previousIndices.Count > 0 ? previousIndices.Dequeue() : Guid.NewGuid().ToString();
        }
    }
}

Home/RealGoTo.cshtml视图，是点击"到别的地方转转"后跳转到的页面，仅仅提供了一个跳转到Home/Index视图页的链接。

复制
@{
    ViewBag.Title = "RealGoTo";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
<h2>RealGoTo</h2>
@Html.ActionLink("回到表单页","Index","Home")

本篇的源码在这里： https://github.com/darrenji/KeepFormStateUsingSession