ASP.NET MVC中使用Session来保持表单的状态

本篇实践在ASP.NET MVC 4下使用Session来保持表单的状态。本篇的源码在这里： https://github.com/darrenji/KeepFormStateUsingSession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：

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：

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，

@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)">添加球员</a>

<br/><br/>

    <div>

        <a href="javascript:void(0)"  id="gotoOther">到别的地方转转</a>  

        <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：

//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);

具体原理，请参考"Applying unobtrusive jquery validation to dynamic content in ASP.Net MVC"这篇文章。在HomeController中，

   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。

<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。

@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：

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();

    }

}

}

其原理，请参考"MVC批量更新,可验证并解决集合元素不连续控制器接收不完全的问题"这篇文章。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。

@{

    ViewBag.Title = "RealGoTo";

Layout = "~/Views/Shared/_Layout.cshtml";

}

<h2>RealGoTo</h2>

@Html.ActionLink("回到表单页","Index","Home")

就这样。