原文:MVC生成CheckBoxList并对其验证

通过扩展方法，可以让CheckBox水平排列，生成CheckBoxList，正如"MVC扩展生成CheckBoxList并水平排列"一文。但，如何对生成的CheckBoxList验证呢？比如要求至少勾选一项：

□ 思路

在强类型视图页中，@Html.EditorFor(model => model.属性, "模版名称", new{ ...路由数据...})，模版名称对应Views/Shared/EditorTemplates/CheckBoxList.cshtml部分视图，路由数据用来传递生成CheckBoxList所需要的一切，并在CheckBoxList.cshtml中显示错误信息，最后CheckBoxList的生成交给扩展方法。

□ Model

public class Course
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

using System.ComponentModel.DataAnnotations;

namespace MvcApplication1.Models
{
    public class Student
    {
        [Display(Name = "姓名")]
        [Required(ErrorMessage = "必填")]
        [StringLength(100, ErrorMessage = "最大长度100")]
        public string Name { get; set; }

[Display(Name = "所选课程")]
        [Required(ErrorMessage = "至少选择一个课程")]
        public string Courses{ get; set; }
    }
}

□ 在_Layout.cshtml中启用客户端异步验证

@Scripts.Render("~/bundles/jquery")
    @Scripts.Render("/bundles/jqueryval") //启用客户端异步验证
    @RenderSection("scripts", required: false)

□ Home/Index.cshtml

@using MvcApplication1.Infrastructure.Enums
@model MvcApplication1.Models.Student
 
@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
 
@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)
 
    <fieldset>
        <legend>Student</legend>
        <div class="editor-label">
            @Html.LabelFor(model => model.Name)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Name)
            @Html.ValidationMessageFor(model => model.Name)
        </div>
        
        <div class="editor-label">
            @Html.LabelFor(model => model.Courses)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Courses, "CheckBoxList", new
            {
                TagName = "Courses",
                CheckBoxItems = ViewBag.Course,
                Position = Position.Horizontal,
                Numbers = 3
            })
        </div>
        
        <p>
            <input type="submit" value="创建"/>
        </p>
    </fieldset>
}

其中，用到了有关CheckBoxList水平或垂直排列的一个枚举：

namespace MvcApplication1.Infrastructure.Enums
{
    public enum Position
    {
        Horizontal,
        Vertical
    }
}

生成CheckBoxList的路由数据，以及模版名称：

@Html.EditorFor(model => model.Courses, "CheckBoxList", new
            {
                TagName = "Courses",
                CheckBoxItems = ViewBag.Course,
                Position = Position.Horizontal,
                Numbers = 3
            })

□ Views/Shared/EditorTemplates/CheckBoxList.cshtml

@using MvcApplication1.Infrastructure.Enums
@{
    var required = false;
    object validationMessage = string.Empty;
 
    //获取客户端验证属性
    var validationAttributes = Html.GetUnobtrusiveValidationAttributes(""); 
    if (validationAttributes.ContainsKey("data-val") && validationAttributes.ContainsKey("data-val-required"))
    {
        required = true;
        if (!validationAttributes.TryGetValue("data-val-required", out validationMessage))
        {
            validationMessage = "This field is required.";
        }
        validationAttributes.Add("required","required");
    }
 
    var tagName = ViewData["TagName"] == null ? "CheckBoxList" : (string)ViewData["TagName"];
    var checkboxItems = ViewData["CheckBoxItems"] == null ? new List<SelectListItem>() : (IEnumerable<SelectListItem>)ViewData["CheckBoxItems"];
    var position = ViewData["Position"] == null ? Position.Horizontal : (Position)ViewData["Position"];
 
    var numbers = 0;
    if (ViewData["Numbers"] == null)
    {
        numbers = 1;
    }
    else if (!int.TryParse(ViewData["Numbers"].ToString(), out numbers))
    {
        numbers = 1;
    }
    else
    {
        numbers = (int)ViewData["Numbers"];
    }
}
 
@Html.CheckBoxList(
tagName,
checkboxItems,
new RouteValueDictionary(validationAttributes),
position,
numbers)
 
@if (required)
{
    <span class="field-validation-valid" data-valmsg-for="@(tagName)" data-valmsg-replace="false">
        @validationMessage
    </span>
}

□ 生成CheckBoxList的扩展方法

using System.Collections.Generic;
using System.Linq;
using System.Text;
using MvcApplication1.Infrastructure.Enums;
 
namespace System.Web.Mvc
{
    public static class CheckBoxListExtensions
    {
        #region 水平方向
        /// <summary>
        /// CheckBoxList
        /// </summary>
        /// <param name="htmlHelper">HTML helper</param>
        /// <param name="name"></param>
        /// <param name="listInfo"></param>
        /// <param name="htmlAttributes"></param>
        /// <param name="number">每行显式的个数</param>
        /// <returns></returns>
        public static MvcHtmlString CheckBoxList(this HtmlHelper htmlHelper,
            string name,
            IEnumerable<SelectListItem> listInfo,
            IDictionary<string, object> htmlAttributes,
            int number)
        {
            if (string.IsNullOrEmpty(name))
            {
                throw new ArgumentException("必须给CheckBoxList一个name值", "name");
            }
            if (listInfo == null)
            {
                throw new ArgumentNullException("listInfo", "List<SelectListItem> listInfo不能为null");
            }
 
            var selectListItems = listInfo as SelectListItem[] ?? listInfo.ToArray();
            if (!selectListItems.Any())
            {
                throw new ArgumentException("List<SelectListItem> listInfo 至少有一组资料", "listInfo");
            }
 
            var sb = new StringBuilder();
            var lineNumber = 0;
            foreach (var info in selectListItems)
            {
                lineNumber++;
                var builder = new TagBuilder("input");
                if (info.Selected)
                {
                    builder.MergeAttribute("checked", "checked");
                }
                builder.MergeAttributes(htmlAttributes);
                builder.MergeAttribute("type", "checkbox");
                builder.MergeAttribute("value", info.Value);
                builder.MergeAttribute("name", name);
                builder.MergeAttribute("id", string.Format("{0}_{1}", name, info.Value));
                sb.Append(builder.ToString(TagRenderMode.Normal));
 
                var labelBuilder = new TagBuilder("label");
                labelBuilder.MergeAttribute("for", string.Format("{0}_{1}", name, info.Value));
                labelBuilder.InnerHtml = info.Text;
                sb.Append(labelBuilder.ToString(TagRenderMode.Normal));
 
                if (number == 0 || (lineNumber % number == 0))
                {
                    sb.Append("<br />");
                }
            }
            return MvcHtmlString.Create(sb.ToString());
        }
 
        public static MvcHtmlString CheckBoxList(this HtmlHelper htmlHelper,
            string name,
            IEnumerable<SelectListItem> listInfo)
        {
            return htmlHelper.CheckBoxList(name, listInfo, (IDictionary<string, object>) null, 0);
        }
        #endregion
 
        #region 垂直方向
 
        public static MvcHtmlString CheckBoxListVertical(this HtmlHelper htmlHelper,
            string name,
            IEnumerable<SelectListItem> listInfo,
            IDictionary<string, object> htmlAttributes,
            int columnNumber = 1)
        {
            if (string.IsNullOrEmpty(name))
            {
                throw new ArgumentException("必须给CheckBoxList的name属性赋值", "name");
            }
            if (listInfo == null)
            {
                throw new ArgumentNullException("listInfo", "List<SelectListInfo> listInfo不能为null");
            }
 
            var selectListItmes = listInfo as SelectListItem[] ?? listInfo.ToArray();
            if (!selectListItmes.Any())
            {
                throw new ArgumentException("List<SelectListItem> listInfo不能为null","listInfo");
            }
 
            var dataCount = selectListItmes.Count();
            var rows = Convert.ToInt32(Math.Ceiling(Convert.ToDecimal(dataCount)/Convert.ToDecimal(columnNumber)));
            if (dataCount <= columnNumber || dataCount - columnNumber == 1)
            {
                rows = dataCount;
            }
 
            var wrapBuilder = new TagBuilder("div");
            wrapBuilder.MergeAttribute("style","float:left; line-height:25px; padding-right:5px;");
            var wrapStart = wrapBuilder.ToString(TagRenderMode.StartTag);
            var wrapClose = string.Concat(wrapBuilder.ToString(TagRenderMode.EndTag),
                " <div style=\"clear:both;\"></div>");
            var wrapBreak = string.Concat("</div>", wrapBuilder.ToString(TagRenderMode.StartTag));
 
            var sb = new StringBuilder();
            sb.Append(wrapStart);
 
            var lineNumber = 0;
            foreach (var info in selectListItmes)
            {
                var builder = new TagBuilder("input");
                if (info.Selected)
                {
                    builder.MergeAttribute("checked","checked");
                }
                builder.MergeAttributes(htmlAttributes);
                builder.MergeAttribute("type","checkbox");
                builder.MergeAttribute("value", info.Value);
                builder.MergeAttribute("name", name);
                builder.MergeAttribute("id", string.Format("{0}_{1}",name, info.Value));
                sb.Append(builder.ToString(TagRenderMode.Normal));
 
                var labelBuilder = new TagBuilder("label");
                labelBuilder.MergeAttribute("for", string.Format("{0}_{1}", name, info.Value));
                labelBuilder.InnerHtml = info.Text;
                sb.Append(labelBuilder.ToString(TagRenderMode.Normal));
 
                lineNumber++;
 
                if (lineNumber.Equals(rows))
                {
                    sb.Append(wrapBreak);
                    lineNumber = 0;
                }
                else
                {
                    sb.Append("<br />");
                }
            }
            sb.Append(wrapClose);
            return MvcHtmlString.Create(sb.ToString());
        }
        #endregion
 
        #region 水平或垂直方向
 
        public static MvcHtmlString CheckBoxList(this HtmlHelper htmlHelper,
            string name,
            IEnumerable<SelectListItem> listInfo,
            IDictionary<string, object> htmlAttributes,
            Position position = Position.Horizontal,
            int number = 0)
        {
            if (string.IsNullOrEmpty(name))
            {
                throw new ArgumentException("必须给CheckBoxList的name属性赋值","name");
            }
            if (listInfo == null)
            {
                throw new ArgumentNullException("listInfo", "List<SelectListItem> listInfo不能为null");
            }
            var selectListItems = listInfo as SelectListItem[] ?? listInfo.ToArray();
            if (!selectListItems.Any())
            {
                throw new ArgumentException("List<SelectListItem> listInfo至少要一组资料","listInfo");
            }
 
            var sb = new StringBuilder();
            var lineNumber = 0;
            switch (position)
            {
                case Position.Horizontal:
                    foreach (var info in selectListItems)
                    {
                        lineNumber++;
                        sb.Append(CreateCheckBoxItem(info, name, htmlAttributes));
 
                        if (number == 0 || (lineNumber%number == 0))
                        {
                            sb.Append("<br />");
                        }
                    }
                    sb.Append("<br />");
                    break;
                case Position.Vertical:
                    var dataCount = selectListItems.Count();
                    var rows = Convert.ToInt32(Math.Ceiling(Convert.ToDecimal(dataCount)/Convert.ToDecimal(number)));
                    if (dataCount <= number || dataCount - number == 1)
                    {
                        rows = dataCount;
                    }
 
                    var wrapBuilder = new TagBuilder("div");
                    wrapBuilder.MergeAttribute("style","float:left; line-height:25px; padding-right:5px;");
                    var wrapStart = wrapBuilder.ToString(TagRenderMode.StartTag);
                    var wrapClose = string.Concat(wrapBuilder.ToString(TagRenderMode.EndTag), " <div style=\"clear:both;\"></div>");
                    var wrapBreak = string.Concat("</div>", wrapBuilder.ToString(TagRenderMode.StartTag));
                    sb.Append(wrapStart);
 
                    foreach (var info in selectListItems)
                    {
                        lineNumber++;
                        sb.Append(CreateCheckBoxItem(info, name, htmlAttributes));
 
                        if (lineNumber.Equals(rows))
                        {
                            sb.Append(wrapBreak);
                            lineNumber = 0;
                        }
                        else
                        {
                            sb.Append(wrapClose);
                        }
                    }
                    sb.Append(wrapClose);
                    break;
            }
            return MvcHtmlString.Create(sb.ToString());
        }
 
        internal static string CreateCheckBoxItem(SelectListItem info, string name,
            IDictionary<string, object> htmlAttributes)
        {
            var sb = new StringBuilder();
            var builder = new TagBuilder("input");
            if (info.Selected)
            {
                builder.MergeAttribute("checked","checked");
            }
            builder.MergeAttributes(htmlAttributes);
            builder.MergeAttribute("type", "checkbox");
            builder.MergeAttribute("value", info.Value);
            builder.MergeAttribute("name", name);
            builder.MergeAttribute("id", string.Format("{0}_{1}", name, info.Value));
            sb.Append(builder.ToString(TagRenderMode.Normal));
 
            var labelBuilder = new TagBuilder("label");
            labelBuilder.MergeAttribute("for", string.Format("{0}_{1}", name, info.Value));
            labelBuilder.InnerHtml = info.Text;
            sb.Append(labelBuilder.ToString(TagRenderMode.Normal));
 
            return sb.ToString();
        }
        #endregion
    }
}

□ HomeController

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MvcApplication1.Infrastructure.Services;
using MvcApplication1.Models;
 
namespace MvcApplication1.Controllers
{
    public class HomeController : Controller
    {
        private readonly  CourseService service = new CourseService();
 
        private List<SelectListItem> coursesSelectListItems
        {
            get
            {
                var courses = this.service.GetCourses();
                var items = new List<SelectListItem>();
                foreach (var c in courses)
                {
                    items.Add(new SelectListItem()
                    {
                        Value = c.Id.ToString(),
                        Text = c.Name
                    });
                }
                return items;
            }
 
        }
 
        public ActionResult Index()
        {
            ViewBag.Course = this.coursesSelectListItems;
            return View();
        }
 
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Index(Student stu)
        {
            ViewBag.Course = this.coursesSelectListItems;
            if (ModelState.IsValid)
            {
                return View();
            }
            return View(stu);
        }
 
    }
}

□ CouseService.cs

using System.Collections.Generic;
using MvcApplication1.Models;
 
namespace MvcApplication1.Infrastructure.Services
{
    public class CourseService
    {
        public IEnumerable<Course> GetCourses()
        {
            return new List<Course>()
            {
                new Course(){Id = 1, Name = "语文"},
                new Course(){Id = 2, Name = "数学"},
                new Course(){Id = 3, Name = "哲学"},
                new Course(){Id = 4, Name = "英语"},
                new Course(){Id = 5,Name = "法语"},
                new Course(){Id = 6, Name = "物理"},
                new Course(){Id = 7, Name = "化学"},
                new Course(){Id = 8, Name = "工程"}
            };
        }
    }
}

参考资料：
ASP.NET MVC - CheckBoxList与ValidationMessage

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