


How to Efficiently Load Cascading State and City Dropdowns in MVC using AJAX?
Jan 28, 2025 pm 06:16 PM
One way to load two drop -down lists (states and cities) in the MVC is to use the AJAX -level pull -up list method. The following is the improved code version:
Controller
View (using non -invasive javascript)
/// <summary> /// 獲取州列表 /// </summary> /// <returns>州列表,SelectListItem類型</returns> private IEnumerable<SelectListItem> GetStates() { using (var db = new DataEntities()) { return db.States.Select(d => new SelectListItem { Text = d.StateName, Value = d.Id.ToString() }); } } /// <summary> /// 獲取指定州的城市列表 /// </summary> /// <param name="id">州ID</param> /// <returns>城市列表,JSON格式</returns> [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); } }
In this method, we use the operation method to retrieve the cities selected in the state and return it as JSON. On the client, we use non -invasive JavaScript to handle the
incident of the state drop -down list and dynamically fill the city's drop -down list. This method provides a better user experience without a complete page refresh. The code was improved, the@model Person @{ ViewBag.Title = "Home Ajax"; IEnumerable<Person> persons = ViewBag.Persons; IEnumerable<SelectListItem> States = ViewBag.States; } @section featured { <div class="content-wrapper"> <hgroup class="title"><h1>@ViewBag.Title</h1></hgroup> </div> } @section styles { td, th { border: 1px solid; padding: 5px 10px; } select { padding: 5px 2px; width: 310px; font-size: 16px; } } @section scripts { @Scripts.Render("~/bundles/jqueryval") <script> var cityStates = @Html.Raw(Json.Encode(ViewBag.CityStates)); // 將CityState JSON轉(zhuǎn)換為JavaScript對(duì)象 $(document).ready(function () { $("#ddlState").change(function () { loadCities(this); }); loadCities($("#ddlState")[0]); // 頁面加載時(shí)初始化城市下拉列表 }); function loadCities(obj) { var stateId = parseInt($(obj).val()); var cities = cityStates.find(v => v.Id === stateId)?.Cities; if (cities) { fillCity(cities); } else { $("#ddlCity").empty(); // 清空城市下拉列表 } } function fillCity(cities) { $("#ddlCity").empty(); // 清空城市下拉列表 $.each(cities, function (index, city) { $("#ddlCity").append($("<option></option>").val(city.Id).text(city.CityName)); }); } function Edit(obj, Id) { $("input[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()); $("#ddlState").val($("td[data-id='cn'] input[type='hidden']", tr).val()); loadCities($("#ddlState")[0]); // 更新城市下拉列表 } </script> } <h3></h3>situation of
was processed, and the filling method of the urban drop -down list was optimized. The initialization operation of the page loading is added to ensure that the city drop -down list is also correctly filled when the page is loaded. GetCities
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