在MVC中使用SelectList中的选定值来保留值时无用

Question

我试图让我的Html.DropDownList保留一些用户选择的值。

代码将使用SelectList中的选定值来保留值，以使下拉列表保留用户先前选择的值。该页面是在MVC环境下构建的。在尝试了一段时间后，我发现网页只能返回到其原始状态(在用户选择任何内容之前)，但在按下提交按钮后无法保留任何下拉列表值。

我还使用jQuery来控制多个下拉列表的显示和隐藏，我只需要一个组下拉列表就可以显示，并且当值被选中时显示另一个下拉列表(零售，公交车，自行车，轨道等)。是组dropdownlist的值和附加dropdownlist的名称)。

下面是我的代码:控制器：

public List<SelectListItem> SetGroup(string group)
        {
            List<SelectListItem> groups = new List<SelectListItem>();
            groups.AddRange(new SelectList(GMManager.FindAllGroup(), "MerchantNo", "MerchantName", group));
            groups.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return groups;

        }

        public List<SelectListItem> SetRetail(string retail)
        {
            List<SelectListItem> retails = new List<SelectListItem>();
            retails.AddRange(new SelectList(GMManager.FindAllRetail(), "MerchantNo", "MerchantName",retail));
            retails.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return retails;

        }

        public List<SelectListItem> SetBus(string bus)
        {
            List<SelectListItem> buses = new List<SelectListItem>();
            buses.AddRange(new SelectList(GMManager.FindAllBus(), "MerchantNo", "MerchantName",bus));
            buses.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return buses;

        }

        public List<SelectListItem> SetBike(string bike)
        {
            List<SelectListItem> bikes = new List<SelectListItem>();
            bikes.AddRange(new SelectList(GMManager.FindAllBike(), "MerchantNo", "MerchantName",bike));
            bikes.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return bikes;

        }

        public List<SelectListItem> SetTrack(string track)
        {
            List<SelectListItem> tracks = new List<SelectListItem>();
            tracks.AddRange(new SelectList(GMManager.FindAllTrack(), "MerchantNo", "MerchantName",track));
            tracks.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return tracks;

        }

        public List<SelectListItem> SetParking(string parking)
        {
            List<SelectListItem> parkings = new List<SelectListItem>();
            parkings.AddRange(new SelectList(GMManager.FindAllParking(), "MerchantNo", "MerchantName",parking));
            parkings.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return parkings;

        }

        public List<SelectListItem> SetOutsourcing(string outsourcing)
        {
            List<SelectListItem> outsourcings = new List<SelectListItem>();
            outsourcings.AddRange(new SelectList(GMManager.FindAllOutsourcing(), "MerchantNo", "MerchantName",outsourcing));
            outsourcings.Add(new SelectListItem() { Text = "ALL", Value = "ALL", Selected = false });
            return outsourcings;

        }  


public ActionResult RPT_160501()
        {
           string start = DateTime.Now.ToString("yyyyMMdd");
            string end = DateTime.Now.ToString("yyyyMMdd");
            string group = "";
            string retail = "";
            string bus = "";
            string bike = "";
            string track = "";
            string parking = "";
            string outsourcing = "";

            DataTable dt = null;



                if (Request.Form["searchConfirm"] != null || Request.Form["ExportExcel"] != null)
                {
                    start = Request.Form["startDate"];
                    end = Request.Form["endDate"];

                    group = Request.Form["group"];
                    retail = Request.Form["retail"];
                    bus = Request.Form["bus"];
                    bike = Request.Form["bike"];
                    track = Request.Form["track"];
                    parking = Request.Form["parking"];
                    outsourcing = Request.Form["outsourcing"];
                }

                ViewBag.Group = SetGroup(group);
                ViewBag.Retail = SetRetail(retail);
                ViewBag.Bus = SetBus(bus);
                ViewBag.Bike = SetBike(bike);
                ViewBag.Track = SetTrack(track);
                ViewBag.Parking = SetParking(parking);
                ViewBag.Outsourcing = SetOutsourcing(outsourcing);

                ViewBag.RepName = "ReportName";
                ViewBag.Start = start;
                ViewBag.End = end;

查看：

<script>
    $(document).ready(function () {
        $("#retail").hide();
        $("#bus").hide();
        $("#bike").hide();
        $("#track").hide();
        $("#parking").hide();
        $("#outsourcing").hide();
        $("#group").on("change", function () {
            switch ($(this).val()) {
                case "RETAIL":
                    $("#retail").show();
                    $("#bus").hide();
                    $("#bike").hide();
                    $("#track").hide();
                    $("#parking").hide();
                    $("#outsourcing").hide();
                    break;
                case "BUS":
                    $("#retail").hide();
                    $("#bus").show();
                    $("#bike").hide();
                    $("#track").hide();
                    $("#parking").hide();
                    $("#outsourcing").hide();
                    break;
                case "BIKE":
                    $("#retail").hide();
                    $("#bus").hide();
                    $("#bike").show();
                    $("#track").hide();
                    $("#parking").hide();
                    $("#outsourcing").hide();
                    break;
                case "TRACK":
                    $("#retail").hide();
                    $("#bus").hide();
                    $("#bike").hide();
                    $("#track").show();
                    $("#parking").hide();
                    $("#outsourcing").hide();
                    break;
                case "PARKING_LOT":
                    $("#retail").hide();
                    $("#bus").hide();
                    $("#bike").hide();
                    $("#track").hide();
                    $("#parking").show();
                    $("#outsourcing").hide();
                    break;
                case "BANK_OUTSOURCING":
                    $("#retail").hide();
                    $("#bus").hide();
                    $("#bike").hide();
                    $("#track").hide();
                    $("#parking").hide();
                    $("#outsourcing").show();
                    break;
                default:
                    $("#retail").hide();
                    $("#bus").hide();
                    $("#bike").hide();
                    $("#track").hide();
                    $("#parking").hide();
                    $("#outsourcing").hide();
                    break;
            }
        })
    })

</script>


<meta name="viewport" content="width=device-width" />
<title>@ViewBag.RepName</title>

<h2>@ViewBag.RepName</h2>



@using (Html.BeginForm("RPT_160501", "ReportSystem", FormMethod.Post, new { id = "searchForm" }))
{
    <div>
        <label for="startDate"> Date:</label>
        <input type="text" name="StartDate" id="StartDate" value="@ViewBag.Start" style="width:100px;" /> ~
        <input type="text" name="EndDate" id="EndDate" value="@ViewBag.End" style="width:100px;" />


        @Html.DropDownList("group", (IEnumerable<SelectListItem>)ViewBag.Group, "--Please Choose--")
        @Html.DropDownList("retail", (IEnumerable<SelectListItem>)ViewBag.Retail, "--Please Choose--")
        @Html.DropDownList("bus", (IEnumerable<SelectListItem>)ViewBag.Bus, "--Please Choose--")
        @Html.DropDownList("bike", (IEnumerable<SelectListItem>)ViewBag.Bike, "--Please Choose--")
        @Html.DropDownList("track", (IEnumerable<SelectListItem>)ViewBag.Track, "--Please Choose--")
        @Html.DropDownList("parking", (IEnumerable<SelectListItem>)ViewBag.Parking, "--Please Choose--")
        @Html.DropDownList("outsourcing", (IEnumerable<SelectListItem>)ViewBag.Outsourcing, "--Plase Choose--")

        <input type="submit" name="searchConfirm" value="Search" class="btn btn-default" />
        <input type="submit" name="ExportExcel" value="Export Excel" class="btn btn-default" />
    </div>
}
<table class="grid" width="100%">
    <thead>
        <tr style="background-color: lightgray">
            <th>
                A
            </th>
            <th>
                B
            </th>
            <th>
                C
            </th>
            <th>
                D
            </th>


        </tr>
    </thead>
    <tbody>

Answer 1

您没有按照预期使用MVC。操作方法MVC应该有一个强类型的ViewModel对象作为参数，允许RPT_160501解析和绑定发布的表单值，而不是您自己做这一切。

同样的道理也适用于视图，它似乎也没有@model声明，因为ViewBag用于所有东西。

在解析和绑定的同时，MVC还会填充全局ModelState对象，MVC还会在内部使用该对象来呈现已发送或尝试的值，只要你使用Html.DropDownListFor(m => m.group, ....) <--这是我对你的问题的回答，但它只有在你整体上采用这种方法时才有效。

当然有一些方法可以在不使用ViewModel的情况下完成所需的工作，但这只会让您在错误的道路上走得更远。最好停在这里，学习正确的方法，然后更轻松地继续进行。

例如，有关此问题的更多信息，请参阅此问题：MVC ViewModel example