asp.net-mvc 如何使用所需的验证创建 ASP.Net MVC DropDownList
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How to create ASP.Net MVC DropDownList with required validation
提问by Diego
I working with mvc 5. I am loading data from Database Using ORM and fill a drop down list from the controller, like this.
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，就像这样。
ViewBag.Country_id = new SelectList(_db.Countries, "Country_id", "Description");
As i wanted an empty field first I am doing this in my HTML.
因为我首先想要一个空字段，所以我在我的 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>
The empty choice has a "0" value.
空选项具有“0”值。
And i wanted to validate the user choose a Country so I add this Validation
我想验证用户选择一个国家，所以我添加了这个验证
[Required,Range(1, int.MaxValue, ErrorMessage = "Error: Must Choose a Country")]
public int Country_id { get; set; }
The Problem is that never get me a Error. Always is "0" and the validation did not occur.
问题是永远不会让我出错。始终为“0”且未进行验证。
What I a missing?
我缺什么？
回答by Win
There are few ways to work with DropDownList. I personallylike to use Strongly-Type ViewModelinstead of ViewBag.
有几种方法可以使用DropDownList。我个人喜欢使用 Strongly-Type ViewModel而不是ViewBag。
Screen Shot
截屏
Validation message displays when submit button is clicked without selecting Country.
单击提交按钮而不选择国家/地区时，将显示验证消息。
Entity
实体
public class Country
{
public int Country_id { get; set; }
public string Description { get; set; }
}
Model
模型
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>();
}
}
Controller
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;
}
}
View
看法
@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>
回答by Diego
Firstly, you cannot get any client side validation using the overload of DropDownList()that you are using. You need to use a different name for the property your binding to and the SelectList. Change the controller code to (say)
首先，您无法使用DropDownList()正在使用的重载进行任何客户端验证。您需要为绑定到的属性和SelectList. 将控制器代码更改为（例如）
ViewBag.CountryList = new SelectList(_db.Countries, "Country_id", "Description");
and change the model property attribute to (delete the RangeAttribute)
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; }
Then in the view use an overload that generates a nulllabel option
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" })
If the user submits the form with the first ("Choose a Country") option selected, a validation error will be displayed.
如果用户提交表单时选择了第一个（“选择国家”）选项，则会显示验证错误。
Side note: It is recommended that you use a view model with a property public IEnumerable<SelectListItem> CountryList { get; set; }rather than ViewBag(and the view becomes @Html.DropDownListFor(m => m.Country_id, Model.CountryList, "Choose a Country", new { @class = "form-control" })
旁注：建议您使用带有属性的视图模型public IEnumerable<SelectListItem> CountryList { get; set; }而不是ViewBag（并且视图变为@Html.DropDownListFor(m => m.Country_id, Model.CountryList, "Choose a Country", new { @class = "form-control" })
回答by Hafsal Rh
Model Class
模型类
[Display(Name = "Program")]
[Required, Range(1, int.MaxValue, ErrorMessage = "Select Program")]
public string Programid { get; set;
View
看法
@Html.DropDownListFor(Model=>Model.Programid,(IEnumerable<SelectListItem>)ViewBag.Program, new {@id = "ddlProgram"})
回答by Tom Stickel
For .net coreinstead of @Html.ValidationMessageFor(...
对于.net 核心而不是@Html.ValidationMessageFor(...
Use
用
razor cshtml
剃须刀 cshtml
<span asp-validation-for="SelectedCountryId" class="text-danger"></span>
model poco
模型 poco
[Required(ErrorMessage = "Country is required.")]
public int SelectedCountryId { get; set; }
