如何使用 DataAnnotation 验证下拉列表？

Question

我需要你的帮助，我在使用 AdataAnnotation 进行验证时遇到问题

我正在尝试使用它来验证下拉列表，但它存在一些问题

这是我的代码

View Side

        @using (Html.BeginForm("addNewProject", "Activities", FormMethod.Post))
        {
            @Html.AntiForgeryToken()


            @Html.ValidationMessage("ProjectName")
            <h3>Project Name: </h3>
            @Html.TextBox("ProjectName", null,  new { @class = "text_field"} )

            @Html.ValidationMessage("ProjectOwner")
            <h3>Project Owner: </h3>
            @Html.DropDownList("ProjectOwner", (SelectList)ViewBag.Customers, new { @class = "text_field" })

            @Html.ValidationMessage("Description")
            <h3>Description: </h3>
            @Html.TextArea("Description", new { @class = "text_area"})

            @Html.ValidationMessage("Department")
            <h3>Departments: </h3>
            @Html.DropDownList("Department", (SelectList)ViewBag.Departments, new { @class = "list" })

            @Html.ValidationMessage("Region")
            <h3>Regions: </h3>
            @Html.DropDownList("Region", (SelectList)ViewBag.Regions, new { @class = "list" })

            <input type="submit" value="Add" class="submit" />
        }

Controller Side

    public ActionResult NewProject()
    {
        List<SelectListItem> list = new List<SelectListItem>();

        list.Add(new SelectListItem() { Value = "0", Text = "Choose ..." });

        list.Add(new SelectListItem() { Value = "1", Text = "First" });

        list.Add(new SelectListItem() { Value = "2", Text = "Second" });

        list.Add(new SelectListItem() { Value = "3", Text = "Third" });

        ViewBag.Departments = new SelectList(list, "Value", "Text");
        ViewBag.Regions = new SelectList(list, "Value", "Text");
        ViewBag.Customers = new SelectList(list, "Value", "Text");

        return View();
    }
    public ActionResult addNewProject(Project newProject)
    {
        if (ModelState.IsValid)
        {

            return RedirectToAction("index", "Home");
        }
        else
        {
            return View("NewProject", newProject);
        }
    }

The Data Holder

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.ComponentModel.DataAnnotations;
namespace workflow.DataHolders
{
    public class Project : DataHolder
    {
        [Required(ErrorMessage = "This Field Is Required")]
        [StringLength(200, MinimumLength = 3, ErrorMessage = "Length Of The Title Should Be More Than 3 Letters")]
        public string ProjectName{ get; set; }

        [Required(ErrorMessage = "This Field Is Required")]
        public List<SelectListItem> ProjectOwner { get; set; }

        string Description { get; set; }

        [Required(ErrorMessage = "This Field Is Required")]
        public List<SelectListItem> Department { get; set; }

        [Required(ErrorMessage = "This Field Is Required")]
        public List<SelectListItem> Region { get; set; }


    }
}

Answer 1

您的代码存在 2 个主要问题。

首先，您尝试将 <select> 绑定到 List<SelectListItem> 的属性，但是 <select> 仅 post 返回单个值类型不能绑定到 List<SelectListItem> 所以属性是 null 并且验证失败。您的属性需要（例如）typeof int 或 string.

其次，您手动添加 SelectListItem 与 Value ="0" 和 Text = "Choose ..." 这意味着即使您更正了第一个问题，如果用户选择了第一个选项（"Choose ...")，您的模型将有效，因为“0”是有效值。

您的 class 需要

public class Project : DataHolder
{
  ....

  [Display(Name = "Project Owner")]
  [Required(ErrorMessage = "Please select a project owner")]
  public int ProjectOwner { get; set; }

  public List<SelectListItem> ProjectOwnerList { get; set; }

  .... // ditto for Department and Region
}

然后在控制器中

public ActionResult NewProject()
{
  List<SelectListItem> list = new List<SelectListItem>();
  list.Add(new SelectListItem() { Value = "1", Text = "First" });
  list.Add(new SelectListItem() { Value = "2", Text = "Second" });
  list.Add(new SelectListItem() { Value = "3", Text = "Third" });
  // Initialize the model
  Project model = new Project();
  model.ProjectOwnerList = list;
  model.DepartmentList = list;
  model.RegionList = list;
  return View(model); // always return a model even if its just a default new instance!
}

请注意您的模型包含 List<SelectListItem> 的属性，因此不要使用 ViewBag，并且在任何情况下，DropDownList() 方法只需要 IEnumerable<SelectListItem> 作为其第二个参数，因此从 List<SelectListItem> 创建一个新的 SelectList 只是不必要的额外开销

然后在视图中

@Html.LabelFor(m => m.ProjectOwner)
@Html.DropDownListFor(m => m.ProjectOwner, Model.ProjectOwnerList, "Choose...")
@Html.ValidationMessageFor(m => m.ProjectOwner)

请注意 DropDownListFor() 的第三个参数添加了一个 labelOption 和 null 值 - <option value>Choose...</option> -，所以如果它被选中，你现在会得到一个错误消息和模型将无效。

假设用户选择"Second"，那么当你post返回时，ProjectOwner的值将是2。

Answer 2

之前的答案是一个很好的答案，但它仍然有一个问题，当它无法验证其中一个字段时会出现问题，它会将您重定向到同一页面，现在您会遇到问题，因为在您的在这种情况下您没有启动任何新列表的代码，因此您将收到错误，因为对象中列表的值为空值。

你的代码可以这样修改来解决这个问题。

Add this to your code to organize it and you could add more than one GetList method depending on your needs.

List<SelectListItem> GetList()
{
    List<SelectListItem> list = new List<SelectListItem>();

    list.Add(new SelectListItem() { Value = "", Text = "Choose ..." });
    list.Add(new SelectListItem() { Value = "1", Text = "First" });
    list.Add(new SelectListItem() { Value = "2", Text = "Second" });
    list.Add(new SelectListItem() { Value = "3", Text = "Third" });

    return list;
}

Modify the addNewProject method to be like this.

public ActionResult addNewProject(Project newProject)
{
    if (ModelState.IsValid)
    {

        return RedirectToAction("index", "Home");
    }
    else
    {

        newProject.ProjectOwnerList = GetList();
        newProject.DepartmentList = GetList();
        newProject.RegionList = GetList();

        return View("NewProject", newProject);
    }
}

请注意，如果使用 DataAnnotation Client Side Validation，您将不会注意到此问题，但即使您使用 Client Side Validation，也必须解决该问题

如何使用 DataAnnotation 验证下拉列表？

how to validate dropdownlist using the DataAnnotation?

data-annotations

asp.net-mvc-4