如何创建需要验证的 ASP.Net MVC DropDownList

Question

我使用 mvc 5。我正在使用 ORM 从数据库加载数据并从控制器填充下拉列表，如下所示。

ViewBag.Country_id = new SelectList(_db.Countries, "Country_id", "Description");

因为我首先想要一个空白字段，所以我在 HTML.

中这样做

<div class="form-group">
    @Html.LabelFor(model => model.Countries, "Country", htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownList("Country_id", null, htmlAttributes: new { @class = "form-control" }, optionLabel: "Choose a Country")
        @Html.ValidationMessageFor(model => model.Country_id, "", new { @class = "text-danger" })
    </div>
</div>

空选项的值为“0”。

我想验证用户选择的国家/地区，所以我添加了此验证

[Required,Range(1, int.MaxValue, ErrorMessage = "Error: Must Choose a Country")]
public int Country_id { get; set; }

问题是永远不会给我一个错误。始终为“0”且未发生验证。

我缺了什么？

Answer 1

使用 DropDownList 的方法很少。我个人喜欢使用强类型ViewModel而不是ViewBag.

屏幕截图

在未选择国家/地区的情况下单击提交按钮时显示验证消息。

实体

public class Country
{
    public int Country_id { get; set; }
    public string Description { get; set; }
}

型号

public class CountryViewModel
{
    [Display(Name = "Country")]
    [Required(ErrorMessage = "{0} is required.")]
    public int SelectedCountryId { get; set; }

    public IList<SelectListItem> AvailableCountries { get; set; }

    public CountryViewModel()
    {
        AvailableCountries = new List<SelectListItem>();
    }
}

控制器

public class HomeController : Controller
{
    public ActionResult Create()
    {
        var countries = GetCountries();
        var model = new CountryViewModel {AvailableCountries = countries};
        return View(model);
    }

    [HttpPost]
    public async Task<ActionResult> Create(CountryViewModel countryViewModel)
    {
        if (ModelState.IsValid)
        {
            int countryId = countryViewModel.SelectedCountryId;
            // Do something
        }
        // If we got this far, something failed. So, redisplay form
        countryViewModel.AvailableCountries = GetCountries();
        return View(countryViewModel);
    }

    public IList<SelectListItem> GetCountries()
    {
        // This comes from database.
        var _dbCountries = new List<Country>
        {
            new Country {Country_id = 1, Description = "USA"},
            new Country {Country_id = 2, Description = "UK"},
            new Country {Country_id = 3, Description = "Canada"},
        };
        var countries = _dbCountries
            .Select(x => new SelectListItem {Text = x.Description, Value = x.Country_id.ToString()})
            .ToList();
        countries.Insert(0, new SelectListItem {Text = "Choose a Country", Value = ""});
        return countries;
    }
}

查看

@model DemoMvc.Models.CountryViewModel
@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Create</title>
</head>
<body>

    <h2>Create</h2>

    @using (Html.BeginForm())
    {
        <div class="form-group">
            @Html.LabelFor(model => model.SelectedCountryId, 
               new {@class = "control-label col-md-2"})
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.SelectedCountryId, 
                    Model.AvailableCountries, new {@class = "form-control"})
                @Html.ValidationMessageFor(model => model.SelectedCountryId, 
                     "", new {@class = "text-danger"})
            </div>
        </div>

        <input type="submit" value="Submit"/>
    }

</body>
</html>

Answer 2

首先，您无法使用您正在使用的 DropDownList() 的重载获得任何客户端验证。您需要为您绑定的属性和 SelectList 使用不同的名称。将控制器代码更改为（例如）

ViewBag.CountryList = new SelectList(_db.Countries, "Country_id", "Description");

并将模型属性属性更改为（删除 RangeAttribute）

 [Required(ErrorMessage = "Error: Must Choose a Country")]
 public int Country_id { get; set; }

然后在视图中使用生成 null 标签选项的重载

@Html.DropDownListFor(m => m.Country_id, (SelectList)ViewBag.CountryList, "Choose a Country", new { @class = "form-control" })

如果用户提交表单时选择了第一个 ("Choose a Country") 选项，将显示验证错误。

旁注：建议您使用属性 public IEnumerable<SelectListItem> CountryList { get; set; } 而不是 ViewBag 的视图模型（并且视图变为 @Html.DropDownListFor(m => m.Country_id, Model.CountryList, "Choose a Country", new { @class = "form-control" })

Answer 3

型号Class

        [Display(Name = "Program")]
        [Required, Range(1, int.MaxValue, ErrorMessage = "Select Program")]
        public string Programid { get; set;

查看

        @Html.DropDownListFor(Model=>Model.Programid,(IEnumerable<SelectListItem>)ViewBag.Program, new {@id = "ddlProgram"})

Answer 4

对于.net core而不是@Html.ValidationMessageFor(...

使用

razor cshtml

<span asp-validation-for="SelectedCountryId" class="text-danger"></span>

型号poco

[Required(ErrorMessage = "Country is required.")]
public int SelectedCountryId { get; set; }

如何创建需要验证的 ASP.Net MVC DropDownList

How to create ASP.Net MVC DropDownList with required validation

asp.net-mvc

validation

html.dropdownlistfor

datamodel

屏幕截图

实体

型号

控制器

查看