如何使用DataAnnotation验证dropdownlist? [英] how to validate dropdownlist using the DataAnnotation?

问题描述

我需要您的帮助，我在使用AdataAnnotation进行验证时遇到了问题

I need your help, I have a problem with the validation using AdataAnnotation

我正在尝试使用它来验证下拉列表，但是存在一些问题

I am trying to validate a dropdown list using it but there is some problem with it

这是我的代码

查看侧

        @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" />
        }

控制器端

    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);
        }
    }

数据持有人

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; }


    }
}

推荐答案

您的代码有2个主要问题.

There are 2 main issues with you code.

首先，您尝试将<select>绑定到List<SelectListItem>的属性，但是<select>仅回发无法绑定到List<SelectListItem>的单个值类型，因此该属性是null验证失败.您的属性必须是(例如)typeof int或string.

First your trying to bind a <select> to a property which is List<SelectListItem>, but a <select> only posts back a single value type which can't be bound to List<SelectListItem> so the property is null and validation fails. Your properties need to be (for example) typeof int or string.

第二，您手动添加带有Value ="0"和Text = "Choose ..."的SelectListItem，这意味着即使更正了第一个问题，如果用户选择了第一个选项(选择...")，您的模型也会之所以有效，是因为"0"是有效值.

Secondly, your manually adding a SelectListItem with Value ="0" and Text = "Choose ..." which means that even if you correct the first issue, if the user selects the first option ("Choose ..."), your model will be valid because "0" is a valid value.

您的课程必须是

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，因此请勿使用ViewBag，并且在任何情况下，DropDownList()方法仅需要IEnumerable<SelectListItem>作为其第二个参数，因此可以从<创建新的SelectList c1>只是不必要的额外开销

Note your model contains properties for List<SelectListItem> so don't use ViewBag, and in any case, the DropDownList() method only requires IEnumerable<SelectListItem> as its second parameter, so creating a new SelectList from List<SelectListItem> is just unnecessary extra overhead

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()的第三个参数会添加一个带有null值的labelOption-<option value>Choose...</option>-，因此，如果选择了该参数，您现在将收到一条错误消息，并且该模型将无效.

Note that the 3rd parameter of DropDownListFor() adds a labelOption with a null value - <option value>Choose...</option> -, so if its selected, youu will now get an error message and the model will be invalid.

假设用户选择"Second"，那么当您发回邮件时，ProjectOwner的值将为2.

Assuming the user selects "Second", then when you post back, the value of ProjectOwner will be 2.

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