未在模型中设置 DropDownListFor 的选定值

Question

我已经搜索了很多小时并尝试了所有的建议。我想我缺少一些基本概念。我想使用模型而不是 ViewBag，并且我在 post 背面的模型中设置了 selected item/value。

我正在 cshtml 中设置 ddl 和操作 link 如下：

@model VinExampleProject.Models.MembersModel

@Html.DropDownListFor(n => n.SearchColumn, new List<SelectListItem>
{
    new SelectListItem {Text = "Select A Column", Value = "1" },
    new SelectListItem {Text = "UserName", Value = "2" },
    new SelectListItem { Text = "FirstName", Value = "3" },
    new SelectListItem { Text = "LastName", Value = "4" }
}
            , "Select A Column")

@Html.ActionLink("Search", "Search", Model)

控制器有这个方法

public ActionResult Search(MembersModel mModel)
{
    // mModel.SearchColumn always 0 or empty string (i have tried both types in the model)
    return RedirectToAction("Index");
}

我希望 mModel.SearchColumn 设置为 select item/value，但始终为空。

这是我的模型：

using System.Collections.Generic;
public class MembersModel 
{
    // public enum SearchColumns { UserName, FirstName, LastName };

    ///<summary>
    /// Gets or sets Customers.
    ///</summary>
    public List<Member> Members { get; set; }

    ///<summary>
    /// Gets or sets CurrentPageIndex.
    ///</summary>
    public int CurrentPageIndex { get; set; }

    ///<summary>
    /// Gets or sets PageCount.
    ///</summary>
    public int MembersPerPage { get; set; }

    ///<summary>
    /// Gets or sets column to sort by.
    ///</summary>
    public string SortColumn { get; set; }

    /// <summary>
    /// Total amount of actib=ve mambers
    /// </summary>
    public int ActiveMemberCount { get; set; }

    /// <summary>
    /// Column to search
    /// </summary>
    public int SearchColumn { get; set; }  // also have tried string here

    /// <summary>
    /// Value to search for
    /// </summary>
    public string SearchValue { get; set; }
}

Answer 1

我猜当您到达 Search 动作时，不仅 SearchColumn 是空的，而且您模型的所有其他属性也是空的。要获取从表单发送到您的操作的值，您需要将它们放入表单并提交表单。

@model VinExampleProject.Models.MembersModel

@using (Html.BeginForm("Search", "Search", FormMethod.Post)) {
    @Html.AntiForgeryToken()
    @Html.DropDownListFor(m => m.SearchColumn, Model.SearchColumnList, "Select A Column")
    <input type="submit" value="SEARCH" />
}

请注意，我还为您添加了 AntiForgeryToken，建议这样做以保护您的网站。我还建议将您的项目列表移至您的模型：

public class MembersModel {
    public IEnumerable<SelectListItem> SearchColumnList { get; set; }
}

并且您的操作必须具有 ValidateAntiForgeryToken 和 HttpPost 属性。您将在 HttpGet 操作中生成列表项作为模型的一部分：

public ActionResult Search() {
    var model = new MembersModel();
    model.SearchColumnList = new List<SelectListItem> {
        new SelectListItem {Text = "Select A Column", Value = "1" },
        new SelectListItem {Text = "UserName", Value = "2" },
        new SelectListItem { Text = "FirstName", Value = "3" },
        new SelectListItem { Text = "LastName", Value = "4" }
    }
    return View(model);
}

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Search(MembersModel model)
{
    //Now your model will be populated with the values from the form
}

如果你真的想使用link，那么你应该考虑使用Ajax。您可以使用 jQuery serialize() 函数在 JavaScript 中序列化您的表单字段，然后通过 Ajax 发送它们。像这样：

<a id="SearchLink" href="#">Search</a>
<script>
    $('#SearchLink).click(function(e) {
      e.preventDefault();
        $.post("@Url.Action("Search", "Search"), $("#myForm").serialize(), function(data) {
            alert("Data sent successfully!");
        });
      return false;
    });
</script>

或者（可能是更好的方法），可以使表单本身成为 Ajax 表单，因此它将通过 Ajax 提交自己并调用 JavaScript 回调函数完成了：

@model VinExampleProject.Models.MembersModel

@using (Ajax.BeginForm("Search", "Search", null, new AjaxOptions {
             OnSuccess = "SearchSuccessCallback(data);",
             OnFailure = "SearchFailureCallback();"
        })) {
    @Html.AntiForgeryToken()
    @Html.DropDownListFor(m => m.SearchColumn, Model.SearchColumnList, "Select A Column")
    <input type="submit" value="SEARCH" />
}
<script>
    function SearchSuccessCallback(data) {
        alert("Data sent successfully!");
    }
    function SearchFailureCallback() {
        alert("There was an error!");
    }
</script>

未在模型中设置 DropDownListFor 的选定值

Selected value for DropDownListFor not being set in model

c#

asp.net

dropdownlistfor

asp.net-mvc-5