我在 MVC 中有这样的模型：
public partial class Magazine
{
public int Id { get; set; }
public int MagYear { get; set; }
public int MagNo { get; set; }
public string MagSeason { get; set; }
public string MagYear2 { get; set; }
}
我想在查看 MagSeason 有一个 DropDownListFor 并填充
Enum Season
{
Spring =0,
Summer =1,
Autumn =2,
Winter=3
}
我该怎么做？
看看我关于这个的博客文章
http://jnye.co/Posts/4/creating-a-dropdown-list-from-an-enum-in-mvc-and-c%23
首先创建一个枚举助手
public static class EnumHelper
{
//Creates a SelectList for a nullable enum value
public static SelectList SelectListFor<T>(T? selected) where T : struct
{
return selected == null ? SelectListFor<T>()
: SelectListFor(selected.Value);
}
//Creates a SelectList for an enum type
public static SelectList SelectListFor<T>() where T : struct
{
Type t = typeof (T);
if (t.IsEnum)
{
var values = Enum.GetValues(typeof(T)).Cast<enum>()
.Select(e => new {
Id = Convert.ToInt32(e),
Name = e.GetDescription()
});
return new SelectList(values, "Id", "Name");
}
return null;
}
//Creates a SelectList for an enum value
public static SelectList SelectListFor<T>(T selected) where T : struct
{
Type t = typeof(T);
if (t.IsEnum)
{
var values = Enum.GetValues(t).Cast<Enum>()
.Select(e => new {
Id = Convert.ToInt32(e),
Name = e.GetDescription()
});
return new SelectList(values, "Id", "Name", Convert.ToInt32(selected));
}
return null;
}
// Get the value of the description attribute if the
// enum has one, otherwise use the value.
public static string GetDescription<TEnum>(this TEnum value)
{
FieldInfo fi = value.GetType().GetField(value.ToString());
if (fi != null)
{
DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attributes.Length > 0)
{
return attributes[0].Description;
}
}
return value.ToString();
}
}
一旦你有了这个帮助类，你就可以执行以下操作。
在您的控制器中：
//If you don't have an enum value use the type
ViewBag.DropDownList = EnumHelper.SelectListFor<MyEnum>();
//If you do have an enum value use the value (the value will be marked as selected)
ViewBag.DropDownList = EnumHelper.SelectListFor(myEnumValue);
在您看来：
@Html.DropDownList("DropDownList")
开始编写您的自定义 html 帮助程序，如下所述，并根据需要更改模板
枚举
public enum Gender {
[Display(Name="Male", Order=0)]
Male,
[Display(Name="Female", Order=1)]
Female
}
看法
@Html.EnumDropDownListFor(m => m.Gender)
然后助手
[AttributeUsage(AttributeTargets.Field)]
public class EnumDisplayNameAttribute : System.ComponentModel.DisplayNameAttribute
{
/// <summary>
/// Sets the display name for an Enum field
/// </summary>
/// <param name="displayName">The display name value to use</param>
public EnumDisplayNameAttribute(string displayName)
: base(displayName)
{
}
}
public static class HtmlHelperExtensions
{
public static MvcHtmlString EnumDropDownList<TEnumType>(this HtmlHelper htmlHelper, string name, TEnumType value)
{
var selectItems = GetSelectItemsForEnum(typeof(TEnumType), value);
return htmlHelper.DropDownList(name, selectItems);
}
public static MvcHtmlString EnumDropDownListPlaceholder<TEnumType>(this HtmlHelper htmlHelper, string name, TEnumType value, string placeholderName = null)
{
var selectItems = GetSelectItemsForEnum(typeof(TEnumType), value);
AddPlaceHolderToSelectItems(placeholderName, selectItems);
return htmlHelper.DropDownList(name, selectItems, new { @class = "placeholder" });
}
public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IDictionary<string, object> htmlAttributes = null) where TModel : class
{
var memberExpression = expression.Body as MemberExpression;
if (memberExpression == null)
throw new InvalidOperationException("Expression must be a member expression");
var name = ExpressionHelper.GetExpressionText(expression);
var fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
ModelState currentValueInModelState;
var couldGetValueFromModelState = htmlHelper.ViewData.ModelState.TryGetValue(fullName, out currentValueInModelState);
object selectedValue = null;
if (!couldGetValueFromModelState &&
htmlHelper.ViewData.Model != null)
{
selectedValue = expression.Compile()(htmlHelper.ViewData.Model);
}
var placeholderName = PlaceholderName(memberExpression);
htmlAttributes = ApplyHtmlAttributes(htmlAttributes, placeholderName);
var selectItems = GetSelectItemsForEnum(typeof(TProperty), selectedValue).ToList();
AddPlaceHolderToSelectItems(placeholderName, selectItems);
return htmlHelper.DropDownListFor(expression, selectItems, htmlAttributes);
}
public static MvcHtmlString PlaceholderDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes = null)
where TModel : class
{
var memberExpression = expression.Body as MemberExpression;
if (memberExpression == null)
throw new InvalidOperationException("Expression must be a member expression");
IList<SelectListItem> list = selectList.ToList();
var placeholderName = PlaceholderName(memberExpression);
AddPlaceHolderToSelectItems(placeholderName, list);
htmlAttributes = ApplyHtmlAttributes(htmlAttributes, placeholderName);
return htmlHelper.DropDownListFor(expression, list, string.IsNullOrEmpty(optionLabel) ? null : optionLabel, htmlAttributes);
}
public static IList<SelectListItem> GetSelectItemsForEnum(Type enumType, object selectedValue)
{
var selectItems = new List<SelectListItem>();
if (enumType.IsGenericType &&
enumType.GetGenericTypeDefinition() == typeof(Nullable<>))
{
enumType = enumType.GetGenericArguments()[0];
selectItems.Add(new SelectListItem { Value = string.Empty, Text = string.Empty });
}
var selectedValueName = selectedValue != null ? selectedValue.ToString() : null;
var enumEntryNames = Enum.GetNames(enumType);
var entries = enumEntryNames
.Select(n => new
{
Name = n,
EnumDisplayNameAttribute = enumType
.GetField(n)
.GetCustomAttributes(typeof(EnumDisplayNameAttribute), false)
.OfType<EnumDisplayNameAttribute>()
.SingleOrDefault() ?? new EnumDisplayNameAttribute("")
})
.Select(e => new
{
Value = e.Name,
DisplayName = e.EnumDisplayNameAttribute.DisplayName ?? e.Name
})
.OrderBy(e => e.DisplayName)
.Select(e => new SelectListItem
{
Value = e.Value,
Text = e.DisplayName,
Selected = e.Value == selectedValueName
});
selectItems.AddRange(entries);
return selectItems;
}
public static IEnumerable<string> GetNamesForEnum(Type enumType, object selectedValue)
{
if (enumType.IsGenericType &&
enumType.GetGenericTypeDefinition() == typeof(Nullable<>))
{
enumType = enumType.GetGenericArguments()[0];
}
var enumEntryNames = Enum.GetNames(enumType);
var entries = enumEntryNames
.Select(n => new
{
Name = n,
EnumDisplayNameAttribute = enumType
.GetField(n)
.GetCustomAttributes(typeof(EnumDisplayNameAttribute), false)
.OfType<EnumDisplayNameAttribute>()
.SingleOrDefault() ?? new EnumDisplayNameAttribute("")
})
.Select(e => new
{
Value = e.Name,
DisplayName = e.EnumDisplayNameAttribute.DisplayName ?? e.Name
})
.OrderBy(e => e.DisplayName)
.Select(e => e.Value);
return entries;
}
static string PlaceholderName(MemberExpression memberExpression)
{
var placeholderName = memberExpression.Member
.GetCustomAttributes(typeof(EnumDisplayNameAttribute), true)
.Cast<EnumDisplayNameAttribute>()
.Select(a => a.DisplayName)
.FirstOrDefault();
return placeholderName;
}
static void AddPlaceHolderToSelectItems(string placeholderName, IList<SelectListItem> selectList)
{
if (!selectList.Where(i => i.Text == string.Empty).Any())
selectList.Insert(0, new SelectListItem { Selected = false, Text = placeholderName, Value = string.Empty });
if (!selectList.Any() || selectList[0].Text != string.Empty) return;
selectList[0].Value = "";
selectList[0].Text = placeholderName;
}
static IDictionary<string, object> ApplyHtmlAttributes(IDictionary<string, object> htmlAttributes, string placeholderName)
{
if (!string.IsNullOrEmpty(placeholderName))
{
if (htmlAttributes == null)
{
htmlAttributes = new Dictionary<string, object>();
}
if (!htmlAttributes.ContainsKey("class"))
htmlAttributes.Add("class", "placeholder");
else
{
htmlAttributes["class"] += " placeholder";
}
}
return htmlAttributes;
}
}