ASP.NET MVC中使用Session來保持表單的狀態

本篇實踐在ASP.NET MVC 4下使用Session來保持表單的狀態。

 

本篇的源碼在這里： https://github.com/darrenji/KeepFormStateUsingSession

 

如上，輸入俱樂部名稱，點擊"添加球員"，輸入球員名稱。我們希望，點擊"到別的地方轉轉"跳轉到另外一個視圖頁，當再次返回的時候能保持表單的狀態。

 

點擊"到別的地方轉轉"跳轉到另外一個視圖頁如下：

 

再次返回，表單的狀態被保持了：

 

點擊"提交"按鈕，顯示表單的內容：

 

關於球員，對應的Model為：

 

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

 

關於俱樂部，對應的Model為：

 

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 = "俱樂部名稱")]
        public string Name { get; set; }
        public List<Player> Players { get; set; }
    }
}

 

在Home/Index.cshtml強類型視圖中，

 

@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)">添加球員</a>
    
    <br/><br/>
    
    <div>
        <a href="javascript:void(0)"  id="gotoOther">到別的地方轉轉</a> &nbsp;
        <input type="submit" id="up" value="提交" />
    </div>
}
@section scripts
{
    <script src="~/Scripts/dynamicvalidation.js"></script>
    <script type="text/javascript">
        $(function () {
            //添加關於Player的新行
            $('#addPlayer').on("click", function() {
                createPlayerRow();
            });
            //到別的頁
            $('#gotoOther').on("click", function() {
                if ($('#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("添加失敗，狀態碼：" + 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("添加行失敗，狀態碼：" + status);
                }
            });
        }
    </script>
}

 

以上，
○ 點擊"添加球員"，向控制器發出異步請求，把部分視圖li動態加載到ul中
○ 點擊"到別的地方轉轉",向控制器發出異步請求，正是在這時候，在控制器的Action中，實施把表單的狀態保存到Session中
○ 點擊"提交"按鈕，把表單信息顯示出來

 

另外，當在頁面上點擊"添加球員"，為了讓動態的部分視圖能被驗證，需要引入dynamicvalidation.js，調用其$.validator.unobtrusive.parseDynamicContent('#players li:last', "#myForm")方法，dynamicvalidation.js具體如下：

 

//對動態生成內容客戶端驗證
(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);

 

具體原理，請參考"Applying unobtrusive jquery validation to dynamic content in ASP.Net MVC"這篇文章。

 

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);
        }
        //提交表單
        [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);
                    }
                }
                //刪除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());
        }
        //跳轉之前把表單保存到Session中
        [HttpPost]
        public ActionResult BeforeGoToMustSave(Club club)
        {
            Session[sessionKey] = club;
            return Json(new { msg = true });
        }
        //保存完Club的Session后真正跳轉到的頁面
        public ActionResult RealGoTo()
        {
            return View();
        }
    }

 

以上，
○ 對於接收[HttpGet]請求的Index方法對應的視圖，Session存在就從Session中取出Club實例，否則就創建一個空的club實例
○ 對於接收[HttpPost]請求的Index方法對應的視圖，顯示表單內容之前把對應的Session刪除
○ 添加新行NewPlayerRow方法供顯示或添加用，當Player類型參數為null的時候，實際就是點擊"添加球員"顯示新行
○ BeforeGoToMustSave方法實際是為了在跳轉之前保存Session
○ RealGoTo是點擊"到別的地方轉轉"后真正跳轉的視圖頁

 

另外，所有視圖頁的公共頁Layout.cshtml，必須引用異步驗證的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部分視圖，是在點擊"添加球員"之后動態加載的部分視圖。

 

@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，用到了擴展Extension文件夾下CollectionEditingHtmlExtensions類的擴展方法，如下：

 

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Mvc;
namespace MvcApplication1.Extension
{
    public static class CollectionEditingHtmlExtensions
    {
        //目標生成如下格式
        //<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)
        {
            //構建name="FavouriteMovies.Index"
            string collectionIndexFieldName = string.Format("{0}.Index", collectionName);
            //構建Guid字符串
            string itemIndex = GetCollectionItemIndex(collectionIndexFieldName);
            //構建帶上集合屬性+Guid字符串的前綴
            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;
            //通過構造函數，先把TemplateInfo以及TemplateInfo.HtmlFieldPrefix賦值給私有字段變量，並把集合屬性名稱賦值給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，請參考"MVC批量更新,可驗證並解決集合元素不連續控制器接收不完全的問題"這篇文章。

Home/RealGoTo.cshtml視圖，是點擊"到別的地方轉轉"后跳轉到的頁面，僅僅提供了一個跳轉到Home/Index視圖頁的鏈接。

 

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

 

就這樣。