Asp.net 通过mvc中的控制器启用html下拉列表

我有一个场景，在这个场景中，我必须根据用户的选择执行一些操作 下拉列表

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

对于基本参考，您可以使用国家、州、城市的示例

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

我能够填充国家/地区列表，当时我已将其他两个下拉列表设置为 禁用

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

填充国家/地区后，我要选择该州。该州正在填充

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

两个问题

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

1） 如何在国家ddl恢复其原始状态时保留其状态。 2） 如何通过我的控制器启用下拉菜单

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

myview代码

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

国

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

状态

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>


城市

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

我的控制器代码

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

    public ActionResult InsertData()
    {

        var customers = from c in objDetailEntity.Country
                        select new
                        {
                            c.Cid,
                            c.Cname
                        };

        SelectList countriesList = new SelectList(customers.Take(100), "Cid", "Cname");
        ViewData["ddlCountries"] = countriesList;

        SelectList EmptyState = new SelectList(customers);
        ViewData["ddlState"] = EmptyState;
        ViewData["ddlCities"] = EmptyState;
        Session["ddlSesCountry"] = countriesList;
        return View();

    }




    //
    // POST: /RegisTest/Create

    [HttpPost]
    public ActionResult InsertData(FormCollection collection)
    {
        try
        {
            CountryId = Convert.ToInt16(Request.Form["ddlCountries"]);
            stateid = Convert.ToInt16(Request.Form["ddlState"]);
            if (CountryId > 0 && stateid <= 0)
            {
                var stateslist = from c in objDetailEntity.State
                                 where c.Country.Cid == CountryId
                                 select new
                                 {
                                     c.Sid,
                                     c.Sname
                                 };

                SelectList stateList = new SelectList(stateslist.Take(100), "Sid", "Sname");
                ViewData["ddlState"] = stateList;
                Session["StateList"] = stateList;
                ViewData["ddlCities"] = stateList;
            }

            if (stateid > 0)
            {
                var citieslist = from c in objDetailEntity.City
                                 where c.State.Sid == stateid
                                 select new
                                 {
                                     c.Ctid,
                                     c.Cityname
                                 };

                SelectList cityList = new SelectList(citieslist.Take(100), "Ctid", "Cityname");


                ViewData["ddlCities"] = cityList;
                ViewData["ddlState"] = Session["StateList"];
            }

            ViewData["ddlCountries"] = Session["ddlSesCountry"];



            return View();
        }
        catch
        {
            return View();
        }
    }

public ActionResult InsertData（）
{
var客户=来自objDetailEntity.Country中的c
选择新的
{
c、 Cid，
c、 Cname
};
SelectList countriesList=新的SelectList（customers.Take（100），“Cid”，“Cname”）；
ViewData[“DDLCONTRIES”]=国家列表；
SelectList EmptyState=新的SelectList（客户）；
ViewData[“ddlState”]=清空状态；
ViewData[“ddlCities”]=清空状态；
会话[“ddlSesCountry”]=国家列表；
返回视图（）；
}
//
//POST:/RegisTest/Create
[HttpPost]
公共操作结果插入数据（FormCollection集合）
{
尝试
{
CountryId=Convert.ToInt16（Request.Form[“ddlCountries]”）；
stateid=Convert.ToInt16（Request.Form[“ddlState”]）；
如果（CountryId>0&&stateid 0）
{
var citieslist=来自objDetailEntity.City中的c
其中c.State.Sid==stateid
选择新的
{
c、 Ctid，
c、 城市名称
};
SelectList cityList=新建SelectList（citieslist.Take（100），“Ctid”，“Cityname”）；
ViewData[“城市”]=城市列表；
ViewData[“ddlState”]=会话[“状态列表”]；
}
ViewData[“ddlseCountries”]=会话[“ddlseCountries”]；
返回视图（）；
}
接住
{
返回视图（）；
}
}

我的选择是根本不发回表单。我将在控制器中编写一个操作，该操作获取一个CountryID并返回一个包含状态列表的JsonResult。onchange事件可以调用jQuery函数，该函数使用AJAX调用此操作，加载新列表，并启用第二个下拉列表

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

但是，如果您坚持使用回发，以下是它不起作用的原因：

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

国家/地区列表没有保留其选定值，因为每次都会从头重新加载视图，并且您将其设置为“未选定”。SelectList构造函数有一个重载，该重载将“SelectedItem”对象作为第四个参数。初始化SelectList时，应将适当的值传递给此参数，而不是在视图中强制执行

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

您需要在视图中编写一个“if”子句，以根据某些条件选择是否启用列表。您可以绑定到具有布尔属性（如“EnableStates”）的ViewModel，或者可以使用状态列表中的值计数之类的内容—例如，如果计数大于零，请启用它

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

---

当您从Web表单转移到MVC时，需要习惯的一件棘手的事情是您不再具有ViewState—您的应用程序是无状态的。没有任何东西可以“记住”在下拉列表中为您选择的值，您必须在每次加载页面时对其进行设置。

我建议使用JSON&jQuery-like

     <p>
        <label>
            State</label>
        <%=Html.DropDownList("ddlState", ViewData["ddlState"] as SelectList, "--not selected--",new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>

     <p>
        <label>
            City</label>
        <%=Html.DropDownList("ddlCities", ViewData["ddlCities"] as SelectList, "--not selected--", new { onchange = "document.forms[0].submit()", disabled = "disabled" })%>
    </p>