如何使用所需的验证创建ASP.Net MVC DropDownList [英] How to create ASP.Net MVC DropDownList with required validation
本文介绍了如何使用所需的验证创建ASP.Net MVC DropDownList的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在使用mvc5.我正在使用ORM从数据库中加载数据，并从控制器中填充一个下拉列表，就像这样.
ViewBag.Country_id = new SelectList(_db.Countries, "Country_id", "Description");
因为我首先想要一个空字段，所以我正在用HTML进行此操作.
<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".
我想验证用户选择一个国家，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，永远不会让我出错.始终为"0"，并且没有进行验证.
我缺少什么?
解决方案
使用 DropDownList 的方法很少.我个人喜欢使用Strongly-Type ViewModel ，而不是 ViewBag .. >
屏幕截图
单击提交按钮但未选择国家/地区时，将显示验证消息.
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>
I working with mvc 5. I am loading data from Database Using ORM and fill a drop down list from the controller, like this.
ViewBag.Country_id = new SelectList(_db.Countries, "Country_id", "Description");
As i wanted an empty field first I am doing this in my HTML.
<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.
And i wanted to validate the user choose a Country so I add this Validation
[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.
What I a missing?
解决方案
There are few ways to work with DropDownList. I personally like to use Strongly-Type ViewModel instead of ViewBag.
Screen Shot
Validation message displays when submit button is clicked without selecting Country.
Entity
public class Country
{
public int Country_id { get; set; }
public string Description { get; set; }
}
Model
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
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
@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>
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