Question

这就是我在页面加载状态和城市下拉列表中加载的方式：

我的控制器方法：

这是第一个在加载页面时调用的方法。

public ActionResult Index()
{
    var states = GetStates();
    var cities =  Enumerable.Empty<SelectListItem>();
    ViewBag.States = states;
    ViewBag.Cities = cities;
}

private IEnumerable<SelectListItem> GetStates()
{
    using (var db = new DataEntities())
    {
        return db.States.Select(d => new SelectListItem { Text = d.StateName, Value =d.Id.ToString() });
    }
}

[HttpGet]
public ActionResult GetCities(int id)
{
    using (var db = new DataEntities())
    {
        var data = db.Cities.Where(d=>d.StateId==id).Select(d => new { Text = d.CityName, Value = d.Id }).ToList();
        return Json(data, JsonRequestBehavior.AllowGet);
    }
}

我的观点：

IEnumerable<SelectListItem> States = ViewBag.States;
IEnumerable<SelectListItem> Cities = ViewBag.Cities;

@Html.DropDownList("State", States, "Select State", new { onchange="loadCities(this)"})
@Html.DropDownListFor(m => m.CityId, Cities, "Select City", new { id="ddlCity"})
function loadCities(obj) {
            $.ajax({
                url: "/Home/GetCities",
                data: { id: $(obj).val() },
                contentType:"application/json",
                success:function(responce){                   
                    var html = '<option value="0">Select City</option>';
                    $(responce).each(function () {
                        html += '<option value="'+this.Value+'">'+this.Text+'</option>'
                    });
                    $("#ddlCity").html(html);
                }
            });
        }

这样可以更好地加载州和城市下拉列表吗？

public class HomeController : Controller
    {
        public ActionResult Index(int id=0)
        {
            Person model = null;
            var states = GetStates().ToList();
            var cities =  Enumerable.Empty<SelectListItem>();
            if (id > 0)
            {
                using (var db = new  DataEntities())
                {
                    model = db.People.Include("City").FirstOrDefault(d => d.Id == id);
                    if (model == null)
                        model = new Person();
                    else
                    {
                       states.First(d => d.Value == model.City.StateId.ToString()).Selected = true;
                       cities = db.Cities.Where(d => d.StateId == model.City.StateId).ToList().Select(d => new SelectListItem { Text = d.CityName,Value=d.Id.ToString(),Selected=d.Id==model.CityId });
                    }

                }
            }
            else
            {
                model = new Person();
            }
            ViewBag.States = states;
            ViewBag.Cities = cities;
            ViewBag.Persons = GetPersons();
            return View(model);
        }

        [HttpGet]
        public ActionResult GetCities(int id)
        {
            using (var db = new DataEntities())
            {
                var data = db.Cities.Where(d=>d.StateId==id).Select(d => new { Text = d.CityName, Value = d.Id }).ToList();
                return Json(data, JsonRequestBehavior.AllowGet);
            }
        }

        public ActionResult SavePersonDetail([Bind(Exclude = "Id")] Person model)
        {

            // var employeeDal= new Emploee();
            //employee.firstname=model.

            if (ModelState.IsValid)
            {
                var Id = model.Id;
                int.TryParse(Request["Id"], out Id);
            using (var db = new DataEntities())
            {
                if (Id > 0)
                {
                    var person = db.People.FirstOrDefault(d => d.Id == Id);
                    if (person != null)
                    {
                        model.Id = Id;
                        db.People.ApplyCurrentValues(model);
                    }
                }
                else
                {
                    db.People.AddObject(model);                    
                }
                db.SaveChanges();
                }               
            }
            if (!Request.IsAjaxRequest())
            {
                ViewBag.States = GetStates();
                ViewBag.Persons = GetPersons();
                ViewBag.Cities = Enumerable.Empty<SelectListItem>();
                return View("Index");
            }
            else
            {
                return PartialView("_personDetail",GetPersons());
            }
        }

        public ActionResult Delete(int id)
        {
            using (var db = new DataEntities())
            {
                var model = db.People.FirstOrDefault(d => d.Id == id);
                if (model != null)
                {
                    db.People.DeleteObject(model);
                    db.SaveChanges();
                }                
            }
            if (Request.IsAjaxRequest())
            {
                return Content(id.ToString());
            }
            else
            {
                ViewBag.States = GetStates();
                ViewBag.Persons = GetPersons();
                ViewBag.Cities = Enumerable.Empty<SelectListItem>();
                return View("Index");
            }
        }

        private IEnumerable<SelectListItem> GetStates()
        {
            using (var db = new DataEntities())
            {
               return db.States.ToList().Select(d => new SelectListItem { Text = d.StateName, Value =d.Id.ToString() });
            }
        }

        private IEnumerable<Person> GetPersons()
        {
            using (var db = new DataEntities())
            {
                return db.People.Include("City").Include("City.State").ToList();
            }
        }

        public ActionResult HomeAjax()
        {
            ViewBag.States = GetStates();
            ViewBag.Cities = Enumerable.Empty<SelectListItem>();
            using (var db = new DataEntities())
            {
                var data = db.States.Include("Cities").Select(d => new { Id = d.Id, Name = d.StateName, Cities = d.Cities.Select(x => new { Id=x.Id,Name=x.CityName}) }).ToList();
                ViewBag.CityStateJson = new System.Web.Script.Serialization.JavaScriptSerializer().Serialize(data);
            }
            ViewBag.Persons = GetPersons();
            return View();
        }
    }


@model IEnumerable<Person>
<div>
    <table>
        <tr>
            <th>
                First Name
            </th>
            <th>
                Last Name
            </th>
            <th>
                Email
            </th>
            <th>
                City
            </th>
            <th>
                State
            </th>
            <th>
                Edit
            </th>
        </tr>
    @if (Model.Count() == 0)
    {
        <tr>
            <td colspan="6">
                <h3>No data available</h3>
            </td>
        </tr>
    }
    else { 
    foreach (var item in Model) { 
        <tr data-id="@item.Id">
            <td data-id="fn">@item.FirstName</td>
            <td data-id="ln">@item.LastName</td>
            <td data-id="email">@item.Email</td>
            <td data-id="cn">@item.CityName<input type="hidden" value="@item.CityId" /></td>
            <td>@item.StateName</td>
            <td>
                @if (ViewBag.Title == "Home Ajax" || Request.IsAjaxRequest())
                {
                    <a href="javascript:void(0);" onclick="Edit(this,@item.Id);">Update</a>
                    <span>@Ajax.ActionLink("Delete", "Delete", new { id = item.Id }, new AjaxOptions {OnSuccess="deleteSuccess",OnBegin="showLoader",OnComplete="hideLoader" })</span>

                }
                else { 
                    <span>@Html.ActionLink("Update", "Index", new { id = item.Id })</span>
                    <span>@Html.ActionLink("Delete", "Delete", new { id = item.Id })</span>
                }

            </td>
        </tr>
    }

    }
        </table>
</div>

@model Person

@{
    ViewBag.Title = "Home Ajax";
    IEnumerable<Person> persons = ViewBag.Persons;
    IEnumerable<SelectListItem> States = ViewBag.States;
    IEnumerable<SelectListItem> Cities = ViewBag.Cities;
    IEnumerable<State> fullStates=ViewBag.CityStates;

}

@section featured {
    <section class="featured">
        <div class="content-wrapper">
            <hgroup class="title">
                <h1>@ViewBag.Title.</h1>                
            </hgroup>            
        </div>
    </section>
}

@section styles{
    <style type="text/css">
       td,th {
            border:1px solid;
            padding:5px 10px;
        }

        select {
           padding:5px 2px;
           width:310px;
           font-size:16px;
        }
    </style>
}

@section scripts{
    @Scripts.Render("~/bundles/jqueryval")
    <script type="text/javascript">

        var jsonArray = @Html.Raw(ViewBag.CityStateJson)

        function clearValues() {
            $("input[type='text'],select").val('');
            $("input[type='hidden'][name='Id']").val(0);
        }

        function loadCities(obj) {

            for (var i = 0; i < jsonArray.length; i++) {
                if (jsonArray[i].Id == parseInt($(obj).val())) {
                    fillCity(jsonArray[i].Cities);
                    break;
                }
            }
        }

        function Edit(obj, Id) {
            //  alert("hi")
            $("input[type='hidden'][name='Id']").val(Id);
            var tr = $(obj).closest("tr");
            $("#txtfirstName").val($("td[data-id='fn']", tr).text().trim());
            $("#txtlastName").val($("td[data-id='ln']", tr).text().trim());
            $("#txtemail").val($("td[data-id='email']", tr).text().trim());
            var city = $("td[data-id='cn'] input[type='hidden']", tr).val();
            var state;
            for (var i = 0; i < jsonArray.length; i++) {
                for (var j = 0; j < jsonArray[i].Cities.length; j++) {
                    if (jsonArray[i].Cities[j].Id == parseInt(city)) {
                        state = jsonArray[i].Id;
                        break;
                    }
                }
                if (state) {
                    fillCity(jsonArray[i].Cities);
                    break;
                }
            }
            $("#ddlState").val(state);
            $("#ddlCity").val(city);
        }

        function fillCity(obj) {
            var html = '<option value="0">Select City</option>';
            $(obj).each(function () {
                html += '<option value="' + this.Id + '">' + this.Name + '</option>'
            });
            $("#ddlCity").html(html);
        }

        function deleteSuccess(responce) {
            alert("record deleted successfully");
            $("tr[data-id='" + responce + "']").remove();
        }

        function insertSuccess() {
            alert("Record saved successfully");
            clearValues();
        }

        function showLoader() {
            $("#overlay").show();
        }
        function hideLoader() {
            $("#overlay").hide();
        }
    </script>
}

<h3>Add Personal Detail</h3>
@using (Ajax.BeginForm("SavePersonDetail", "Home", new AjaxOptions { HttpMethod = "POST", UpdateTargetId = "personList" ,OnSuccess="insertSuccess",OnBegin="showLoader",OnComplete="hideLoader"}))
{
    @Html.HiddenFor(m => m.Id);
<ol class="round">
    <li>       
        @Html.LabelFor(m => m.FirstName)
        @Html.TextBoxFor(m => m.FirstName, new { id = "txtfirstName" })
        @Html.ValidationMessageFor(m => m.FirstName)
    </li>
    <li>
    @Html.LabelFor(m => m.LastName)
        @Html.TextBoxFor(m => m.LastName, new { id = "txtlastName" })
        @Html.ValidationMessageFor(m => m.LastName)
        </li>
    <li>
       @Html.LabelFor(m => m.Email)
        @Html.TextBoxFor(m => m.Email, new { id = "txtemail" })
        @Html.ValidationMessageFor(m => m.Email)
    </li>

    <li>
        @Html.Label("State")
       @Html.DropDownList("State", States, "Select State", new { onchange = "loadCities(this)", id = "ddlState" })       
    </li>
    <li>
         @Html.LabelFor(m => m.CityId)
        @Html.DropDownListFor(m => m.CityId, Cities, "Select City", new { id = "ddlCity" })
        @Html.ValidationMessageFor(m => m.CityId)
    </li>
</ol>
    <input type="submit" value="Save" />
    <input type="button" value="Cancel" onclick="clearValues();"/>
}

   <h2>
        Person List
    </h2>
<div style="position:fixed;text-align:center;top:0;bottom:0;left:0;right:0;z-index:10;background-color:black;opacity:0.6;display:none;" id="overlay">
    <img style="position:relative;top:370px" src="~/Images/ajax-loader.gif" />
</div>
<div id="personList">
    @Html.Partial("_personDetail", persons)
    </div>

Answer 1

使用ajax的方法很好，但我建议采用一些更好的做法，包括使用包含StateID，CityID StateList和CityList属性的视图模型，并使用Unobtrusive JavaScript而不是用行为污染您的标记，并生成第一个（＆＃34;请选择＆＃34;）选项，其值为null而非0，因此可以与[Required]属性

HTML

@Html.DropDownList(m => m.StateID, States, "Select State") // remove the onchange
@Html.DropDownListFor(m => m.CityID, Cities, "Select City") // why change the default ID?

SCRIPT

var url = '@Url.Action("GetCities", "Home")'; // use the helper (dont hard code)
var cities = $('#CityID'); // cache the element
$('#StateID').change(function() {
  $.getJSON(url, { id: $(this).val() }, function(response) {
    // clear and add default (null) option
    cities.empty().append($('<option></option>').val('').text('Please select'));
    $.each(response, function(index, item) {
      cities.append($('<option></option>').val(item.Value).text(item.Text));
    });
  });
});

如果您要渲染多个项目（比如说您要求用户选择他们访问过的最近10个城市），您可以缓存第一个呼叫的结果，以避免重复呼叫，其中他们的选择可能包括来自同一州的城市。

var cache = {};
$('#StateID').change(function() {
  var selectedState = $(this).val();
  if (cache[selectedState]) {
    // render the options from the cache
  } else {
    $.getJSON(url, { id: selectedState }, function(response) {
      // add to cache
      cache[selectedState] = response;
      .....
    });
  }
});

最后，为了回应您关于在没有ajax的情况下执行此操作的注释，您可以将所有城市传递到视图并将它们分配给javascript数组。如果你有几个国家，每个国家都有几个城市，我只会推荐这个。这是一个平衡微小的额外初始加载时间与进行ajax调用的轻微延迟的问题。

在控制器中

model.CityList = db.Cities.Select(d => new { City = d.CountryID, Text = d.CityName, Value = d.Id }).ToList();

在视图（脚本）

中

// assign all cities to javascript array
var allCities= JSON.parse('@Html.Raw(Json.Encode(Model.CityList))');
$('#StateID').change(function() {
  var selectedState = $(this).val();
  var cities = $.grep(allCities, function(item, index) {
    return item.CountryID == selectedState;
  });
  // build options based on value of cities
});

Answer 2

这是一种正确的方法，但您可以简化您的javascript：

function loadCities(obj) {
    $.getJSON("/Home/GetCities", function (data) {
        var html = '<option value="0">Select City</option>';
        $(data).each(function () {
              html += '<option value="'+this.Value+'">'+this.Text+'</option>'
        });
        $("#ddlCity").html(html);
    });
}

进一步简化：添加服务器端的默认项目（选择城市），这样您的javascript就会更小。

Answer 3

假设城市列表不长，我在没有页面刷新的情况下如何做到这一点。我假设你可以创建一个GetStatesAndCities方法来返回一个字典。

public ActionResult Index()
{
  Dictionary<string, List<String>> statesAndCities = GetStatesAndCities();
  ViewBag.StatesAndCities = Json(statesAndCities);
}

然后在视图中：

var states = JSON.parse(@ViewBag.StatesAndCities);

function loadCities(obj) {
    var cities = states[$(obj).val()];
    var html = '<option value="0">Select City</option>';
    $(cities).each(function () {
        html += '<option value="'+this.Value+'">'+this.Text+'</option>'
    });
    $("#ddlCity").html(html);
}

这样当状态改变时，cities字段立即更新，不需要回调。

Answer 4

免责声明：这不是代码答案，还有很多其他答案。

我认为最好的方法是让自己乐于从数据中分离UI页面=＆gt;把它们变成API调用：

/ GetCities
/ GETSTATES

现在你可以简单地在Razor渲染页面上留下选择的空白。并使用Jquery / Bootstrap插件创建一个AJAX选择框。

这样当用户停止输入搜索时，可以通过AJAX调用发送此搜索字符串（例如：/GetStates?search=test），然后可以将一小组结果发送回网站。

这给出了：

更好地分离服务代码
更好的用户体验。
较小的页面加载（因为您在请求页面时不再向用户发送所有选项，只有当他打开选择框时）。

Answer 5

如何使用Knockout？

Knockout是一个JavaScript库，可帮助您使用干净的底层数据模型创建丰富的响应式显示和编辑器用户界面

你必须为你的城市使用ajax。但是淘汰你不需要写

var html = '<option value="0">Select City</option>'; $(responce).each(function () { html += '<option value="'+this.Value+'">'+this.Text+'</option>'}); $("#ddlCity").html(html);

你的javascript.Knockout中的

使它变得简单。

您可以简单地写一下：

        function CityModel() {
        var self = this; // that means this CityModel
        self.cities = ko.observableArray([]);
        self.getCities = function () {
            $.ajax({
                url: "/Home/GetCities",
                data: { id: $(obj).val() },
                contentType: "application/json",
                success: self.cities
            });
        }
    }
    ko.applyBindings(new CityModel());

这就是全部。但是您必须将数据绑定到html元素中。而不是使用： @Html.DropDownListFor(m => m.CityId, Cities, "Select City", new { id="ddlCity"})

您可以使用：

    <select data-bind="options:cities,optionsValue:"Id",optionsText:"CityName",optionsCaption:"Select City""></select>

或者你可以混合剃刀和淘汰赛：

@Html.DropDownListFor(m => m.CityId, Cities, "Select City", new { id="ddlCity",data_bind:"options:cities,optionsValue:\"Id\",optionsText:\"CityName\""})

当GetCities发生变化时，您还需要致电State，还可以：

@Html.DropDownList("State", States, "Select State", new {data_bind:"event:\"change\":\"$root.GetCities\""})

不要害怕这个因为"是一个逃脱角色，我们不得不说剃刀我想用“之前使用\”。

您可以找到有关淘汰赛的更多信息：Knockout

与剃刀混合：Razor and Knockout

Ps：是的，使用淘汰赛让我们暂停Razor和Mvc。您必须编写另一个ViewModel。但就像这种情况一样，ko很有帮助。混合剃须刀和淘汰赛是另一种选择。

在mvc中加载2下拉列表的更好方法

5 个答案: