C# 如何使用ajax根据从另一个dropdownlist中选择的值更改dropdownlist中的选项？

在用户从单独的dropdownlist中选择一个选项后，我使用ajax通过一个更改事件更改dropdownlist中的选项，但它根本不会更改选项。这是我的ajax代码，它似乎工作得很好

$(document).ready(function () {
        // if user changes paper type
        $('#paperTypeJList').change(function () {
            var modelData = {
                paperType: $("#paperTypeJList").val(),
                urgency: $("#urgencyJList").val(),
                numOfPages: $("#numOfPagesJList").val()
            };

            $.ajax({
                url: '@Url.Action("changeDropDownValues", "Home")',
                type: "GET",
                data: {paperType:modelData.paperType},
                cache: false,
                async: true,
                success: function (response) {
                    alert("Success");
                }
            });
    });

下面是我用ajax代码调用的方法的代码

public void changeDropDownValues(string paperType)
    {
        List<SelectListItem> urgencyList1 = new List<SelectListItem>();
        urgencyList1.Add(new SelectListItem() { Text = "Select the Urgency", Value = "", Selected = true });
        urgencyList1.Add(new SelectListItem() { Text = "60 Days", Value = "60", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "30 Days", Value = "30", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "20 Days", Value = "20", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "10 Days", Value = "10", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "7 Days", Value = "7", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "5 Days", Value = "5", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "4 Days", Value = "4", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "72 Hours", Value = "72", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "48 Hours", Value = "48", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "24 Hours", Value = "24", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "12 Hours", Value = "12", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "6 Hours", Value = "6", Selected = false });
        urgencyList1.Add(new SelectListItem() { Text = "3 Hours", Value = "3", Selected = false });

        List<SelectListItem> urgencyList2 = new List<SelectListItem>();
        urgencyList2.Add(new SelectListItem() { Text = "Select the Urgency", Value = "", Selected = true });
        urgencyList2.Add(new SelectListItem() { Text = "10 Days", Value = "10", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "7 Days", Value = "7", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "5 Days", Value = "5", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "4 Days", Value = "4", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "72 Hours", Value = "72", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "48 Hours", Value = "48", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "24 Hours", Value = "24", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "12 Hours", Value = "12", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "6 Hours", Value = "6", Selected = false });
        urgencyList2.Add(new SelectListItem() { Text = "3 Hours", Value = "3", Selected = false });

        switch (paperType)
        {
            case "Dissertation":
                ViewBag.urgency = new SelectList(urgencyList1, "Value", "Text");
                break;
            case "Research Proposal":
                ViewBag.urgency = new SelectList(urgencyList1, "Value", "Text");
                break;
            default:
                ViewBag.urgency = new SelectList(urgencyList2, "Value", "Text");
                break;
        }
    }

如果您使用的是WebForms，则应使用Asp.net AJAX控件工具包的级联DropDownList：

这是一个

更新：

如果您在asp.net mvc中工作，可以通过以下方式实现级联下拉列表：

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这就是我需要的，但是你知道asp.NETMVC4的教程吗？我不能让他们的代码工作，因为它是older@FranklinJosephMoormannMVC不再真正需要Ajax控件工具包。尽管该工具包很有用，但ASP.NETMVC有很多工具可以本机实现AJAX驱动的行为。提示：ASP.NETMVC是一个非常重要的问题标签。如果没有它，通常认为常规ASP.Net就是解决问题的方法。是的@Flater这就是我编辑并提供webforms和mvcI的原因，MVC回复了原始海报，并补充说MVC可以很好地处理所有类型的Ajax内容。完整标记的重要性：为了清晰起见，编辑了我之前的评论。