Is there a way to set a constructor optional param?
I mean something like:
User.fromData(this._name,
this._email,
this._token,
this._refreshToken,
this._createdAt,
this._expiresAt,
this._isValid,
{this.id});
It indicates that
Named option parameters can't start with an underscore.
But I need this field as private, so, I'm lost now.
This is a more general answer for future viewers.
Positional optional parameters
Wrap the optional parameter with [ ] square brackets.
class User {
String name;
int age;
String home;
User(this.name, this.age, [this.home = 'Earth']);
}
User user1 = User('Bob', 34);
User user2 = User('Bob', 34, 'Mars');
Optional parameters need to be nullable if you don't provide a default value:
class User {
String name;
int age;
String? home; // <-- Nullable
User(this.name, this.age, [this.home]);
}
Named optional parameters
Wrap the optional parameter with { } curly braces.
class User {
String name;
int age;
String home;
User(this.name, this.age, {this.home = 'Earth'});
}
User user1 = User('Bob', 34);
User user2 = User('Bob', 34, home: 'Mars');
The default for home is "Earth", but like before, if you don't provide a default then you need to change String home to String? home.
Private fields
If you need private fields then you can use [] square brackets:
class User {
int? _id;
User([this._id]);
}
User user = User(3);
or do as the accepted answer says and use an initializer list:
class User {
int? _id;
User({int? id})
: _id = id;
}
User user = User(id: 3);
Named required parameters
Named parameters are optional by default, but if you want to make them required, then you can use the required keyword:
class User {
final String name;
final int age;
final String home;
User({
required this.name,
required this.age,
this.home = 'Earth',
});
}
User user1 = User(name: 'Bob', age: 34);
User user2 = User(name: 'Bob', age: 34, home: 'Mars');
You need to use a simple parameter and initialize your private field in initializer list.
class User {
final String _id;
final String _name;
User.fromData(this._name, {required String id})
: _id = id;
}
In addition to great Suragch's answer I wanted to mention required word. You can use it for multiple constructor or function named parameters to specify required ones.
class User {
int _id;
String _firstName;
String _lastName;
User({required int id, String firstName = "", String lastName})
: _id = id, // required parameter
_firstName = firstName, // optional parameter with default value ""
_lastName = lastName; // optional parameter without default value
}
User user1 = User(id: 1);
User user2 = User(id: 2, firstName: "John");
User user3 = User(id: 3, lastName: "Snow");
Related Dart docs here.
For Dart version <= 2.10 #required is an annotation and used with the # prefix.
I'm trying to use the Html.DropDownList extension method but can't figure out how to use it with an enumeration.
Let's say I have an enumeration like this:
public enum ItemTypes
{
Movie = 1,
Game = 2,
Book = 3
}
How do I go about creating a dropdown with these values using the Html.DropDownList extension method?
Or is my best bet to simply create a for loop and create the Html elements manually?
For MVC v5.1 use Html.EnumDropDownListFor
#Html.EnumDropDownListFor(
x => x.YourEnumField,
"Select My Type",
new { #class = "form-control" })
For MVC v5 use EnumHelper
#Html.DropDownList("MyType",
EnumHelper.GetSelectList(typeof(MyType)) ,
"Select My Type",
new { #class = "form-control" })
For MVC 5 and lower
I rolled Rune's answer into an extension method:
namespace MyApp.Common
{
public static class MyExtensions{
public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
where TEnum : struct, IComparable, IFormattable, IConvertible
{
var values = from TEnum e in Enum.GetValues(typeof(TEnum))
select new { Id = e, Name = e.ToString() };
return new SelectList(values, "Id", "Name", enumObj);
}
}
}
This allows you to write:
ViewData["taskStatus"] = task.Status.ToSelectList();
by using MyApp.Common
I know I'm late to the party on this, but thought you might find this variant useful, as this one also allows you to use descriptive strings rather than enumeration constants in the drop down. To do this, decorate each enumeration entry with a [System.ComponentModel.Description] attribute.
For example:
public enum TestEnum
{
[Description("Full test")]
FullTest,
[Description("Incomplete or partial test")]
PartialTest,
[Description("No test performed")]
None
}
Here is my code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Mvc;
using System.Web.Mvc.Html;
using System.Reflection;
using System.ComponentModel;
using System.Linq.Expressions;
...
private static Type GetNonNullableModelType(ModelMetadata modelMetadata)
{
Type realModelType = modelMetadata.ModelType;
Type underlyingType = Nullable.GetUnderlyingType(realModelType);
if (underlyingType != null)
{
realModelType = underlyingType;
}
return realModelType;
}
private static readonly SelectListItem[] SingleEmptyItem = new[] { new SelectListItem { Text = "", Value = "" } };
public static string GetEnumDescription<TEnum>(TEnum value)
{
FieldInfo fi = value.GetType().GetField(value.ToString());
DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
if ((attributes != null) && (attributes.Length > 0))
return attributes[0].Description;
else
return value.ToString();
}
public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
{
return EnumDropDownListFor(htmlHelper, expression, null);
}
public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression, object htmlAttributes)
{
ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
Type enumType = GetNonNullableModelType(metadata);
IEnumerable<TEnum> values = Enum.GetValues(enumType).Cast<TEnum>();
IEnumerable<SelectListItem> items = from value in values
select new SelectListItem
{
Text = GetEnumDescription(value),
Value = value.ToString(),
Selected = value.Equals(metadata.Model)
};
// If the enum is nullable, add an 'empty' item to the collection
if (metadata.IsNullableValueType)
items = SingleEmptyItem.Concat(items);
return htmlHelper.DropDownListFor(expression, items, htmlAttributes);
}
You can then do this in your view:
#Html.EnumDropDownListFor(model => model.MyEnumProperty)
**EDIT 2014-JAN-23: Microsoft have just released MVC 5.1, which now has an EnumDropDownListFor feature. Sadly it does not appear to respect the [Description] attribute so the code above still stands.See Enum section in Microsoft's release notes for MVC 5.1.
Update: It does support the Display attribute [Display(Name = "Sample")] though, so one can use that.
[Update - just noticed this, and the code looks like an extended version of the code here: https://blogs.msdn.microsoft.com/stuartleeks/2010/05/21/asp-net-mvc-creating-a-dropdownlist-helper-for-enums/, with a couple of additions. If so, attribution would seem fair ;-)]
In ASP.NET MVC 5.1, they added the EnumDropDownListFor() helper, so no need for custom extensions:
Model:
public enum MyEnum
{
[Display(Name = "First Value - desc..")]
FirstValue,
[Display(Name = "Second Value - desc...")]
SecondValue
}
View:
#Html.EnumDropDownListFor(model => model.MyEnum)
Using Tag Helper (ASP.NET MVC 6):
<select asp-for="#Model.SelectedValue" asp-items="Html.GetEnumSelectList<MyEnum>()">
I bumped into the same problem, found this question, and thought that the solution provided by Ash wasn't what I was looking for; Having to create the HTML myself means less flexibility compared to the built-in Html.DropDownList() function.
Turns out C#3 etc. makes this pretty easy. I have an enum called TaskStatus:
var statuses = from TaskStatus s in Enum.GetValues(typeof(TaskStatus))
select new { ID = s, Name = s.ToString() };
ViewData["taskStatus"] = new SelectList(statuses, "ID", "Name", task.Status);
This creates a good ol' SelectList that can be used like you're used to in the view:
<td><b>Status:</b></td><td><%=Html.DropDownList("taskStatus")%></td></tr>
The anonymous type and LINQ makes this so much more elegant IMHO. No offence intended, Ash. :)
Here is a better encapsulated solution:
https://www.spicelogic.com/Blog/enum-dropdownlistfor-asp-net-mvc-5
Say here is your model:
Sample Usage:
Generated UI:
And generated HTML
The Helper Extension Source Code snap shot:
You can download the sample project from the link I provided.
EDIT: Here's the code:
public static class EnumEditorHtmlHelper
{
/// <summary>
/// Creates the DropDown List (HTML Select Element) from LINQ
/// Expression where the expression returns an Enum type.
/// </summary>
/// <typeparam name="TModel">The type of the model.</typeparam>
/// <typeparam name="TProperty">The type of the property.</typeparam>
/// <param name="htmlHelper">The HTML helper.</param>
/// <param name="expression">The expression.</param>
/// <returns></returns>
public static MvcHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
Expression<Func<TModel, TProperty>> expression)
where TModel : class
{
TProperty value = htmlHelper.ViewData.Model == null
? default(TProperty)
: expression.Compile()(htmlHelper.ViewData.Model);
string selected = value == null ? String.Empty : value.ToString();
return htmlHelper.DropDownListFor(expression, createSelectList(expression.ReturnType, selected));
}
/// <summary>
/// Creates the select list.
/// </summary>
/// <param name="enumType">Type of the enum.</param>
/// <param name="selectedItem">The selected item.</param>
/// <returns></returns>
private static IEnumerable<SelectListItem> createSelectList(Type enumType, string selectedItem)
{
return (from object item in Enum.GetValues(enumType)
let fi = enumType.GetField(item.ToString())
let attribute = fi.GetCustomAttributes(typeof (DescriptionAttribute), true).FirstOrDefault()
let title = attribute == null ? item.ToString() : ((DescriptionAttribute) attribute).Description
select new SelectListItem
{
Value = item.ToString(),
Text = title,
Selected = selectedItem == item.ToString()
}).ToList();
}
}
Html.DropDownListFor only requires an IEnumerable, so an alternative to Prise's solution is as follows. This will allow you to simply write:
#Html.DropDownListFor(m => m.SelectedItemType, Model.SelectedItemType.ToSelectList())
[Where SelectedItemType is a field on your model of type ItemTypes, and your model is non-null]
Also, you don't really need to genericize the extension method as you can use enumValue.GetType() rather than typeof(T).
EDIT: Integrated Simon's solution here as well, and included ToDescription extension method.
public static class EnumExtensions
{
public static IEnumerable<SelectListItem> ToSelectList(this Enum enumValue)
{
return from Enum e in Enum.GetValues(enumValue.GetType())
select new SelectListItem
{
Selected = e.Equals(enumValue),
Text = e.ToDescription(),
Value = e.ToString()
};
}
public static string ToDescription(this Enum value)
{
var attributes = (DescriptionAttribute[])value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
return attributes.Length > 0 ? attributes[0].Description : value.ToString();
}
}
So without Extension functions if you are looking for simple and easy.. This is what I did
<%= Html.DropDownListFor(x => x.CurrentAddress.State, new SelectList(Enum.GetValues(typeof(XXXXX.Sites.YYYY.Models.State))))%>
where XXXXX.Sites.YYYY.Models.State is an enum
Probably better to do helper function, but when time is short this will get the job done.
Expanding on Prise and Rune's answers, if you'd like to have the value attribute of your select list items map to the integer value of the Enumeration type, rather than the string value, use the following code:
public static SelectList ToSelectList<T, TU>(T enumObj)
where T : struct
where TU : struct
{
if(!typeof(T).IsEnum) throw new ArgumentException("Enum is required.", "enumObj");
var values = from T e in Enum.GetValues(typeof(T))
select new {
Value = (TU)Convert.ChangeType(e, typeof(TU)),
Text = e.ToString()
};
return new SelectList(values, "Value", "Text", enumObj);
}
Instead of treating each Enumeration value as a TEnum object, we can treat it as a object and then cast it to integer to get the unboxed value.
Note:
I also added a generic type constraint to restrict the types for which this extension is available to only structs (Enum's base type), and a run-time type validation which ensures that the struct passed in is indeed an Enum.
Update 10/23/12:
Added generic type parameter for underlying type and fixed non-compilation issue affecting .NET 4+.
In .NET Core you can just use this:
#Html.DropDownListFor(x => x.Foo, Html.GetEnumSelectList<MyEnum>())
To solve the problem of getting the number instead of text using Prise's extension method.
public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
{
var values = from TEnum e in Enum.GetValues(typeof(TEnum))
select new { ID = (int)Enum.Parse(typeof(TEnum),e.ToString())
, Name = e.ToString() };
return new SelectList(values, "Id", "Name", enumObj);
}
A super easy way to get this done - without all the extension stuff that seems overkill is this:
Your enum:
public enum SelectedLevel
{
Level1,
Level2,
Level3,
Level4
}
Inside of your controller bind the Enum to a List:
List<SelectedLevel> myLevels = Enum.GetValues(typeof(SelectedLevel)).Cast<SelectedLevel>().ToList();
After that throw it into a ViewBag:
ViewBag.RequiredLevel = new SelectList(myLevels);
Finally simply bind it to the View:
#Html.DropDownList("selectedLevel", (SelectList)ViewBag.RequiredLevel, new { #class = "form-control" })
This is by far the easiest way I found and does not require any extensions or anything that crazy.
UPDATE: See Andrews comment below.
The best solution I found for this was combining this blog with Simon Goldstone's answer.
This allows use of the enum in the model. Essentially the idea is to use an integer property as well as the enum, and emulate the integer property.
Then use the [System.ComponentModel.Description] attribute for annotating the model with your display text, and use an "EnumDropDownListFor" extension in your view.
This makes both the view and model very readable and maintainable.
Model:
public enum YesPartialNoEnum
{
[Description("Yes")]
Yes,
[Description("Still undecided")]
Partial,
[Description("No")]
No
}
//........
[Display(Name = "The label for my dropdown list")]
public virtual Nullable<YesPartialNoEnum> CuriousQuestion{ get; set; }
public virtual Nullable<int> CuriousQuestionId
{
get { return (Nullable<int>)CuriousQuestion; }
set { CuriousQuestion = (Nullable<YesPartialNoEnum>)value; }
}
View:
#using MyProject.Extensions
{
//...
#Html.EnumDropDownListFor(model => model.CuriousQuestion)
//...
}
Extension (directly from Simon Goldstone's answer, included here for completeness):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.ComponentModel;
using System.Reflection;
using System.Linq.Expressions;
using System.Web.Mvc.Html;
namespace MyProject.Extensions
{
//Extension methods must be defined in a static class
public static class MvcExtensions
{
private static Type GetNonNullableModelType(ModelMetadata modelMetadata)
{
Type realModelType = modelMetadata.ModelType;
Type underlyingType = Nullable.GetUnderlyingType(realModelType);
if (underlyingType != null)
{
realModelType = underlyingType;
}
return realModelType;
}
private static readonly SelectListItem[] SingleEmptyItem = new[] { new SelectListItem { Text = "", Value = "" } };
public static string GetEnumDescription<TEnum>(TEnum value)
{
FieldInfo fi = value.GetType().GetField(value.ToString());
DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
if ((attributes != null) && (attributes.Length > 0))
return attributes[0].Description;
else
return value.ToString();
}
public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
{
return EnumDropDownListFor(htmlHelper, expression, null);
}
public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression, object htmlAttributes)
{
ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
Type enumType = GetNonNullableModelType(metadata);
IEnumerable<TEnum> values = Enum.GetValues(enumType).Cast<TEnum>();
IEnumerable<SelectListItem> items = from value in values
select new SelectListItem
{
Text = GetEnumDescription(value),
Value = value.ToString(),
Selected = value.Equals(metadata.Model)
};
// If the enum is nullable, add an 'empty' item to the collection
if (metadata.IsNullableValueType)
items = SingleEmptyItem.Concat(items);
return htmlHelper.DropDownListFor(expression, items, htmlAttributes);
}
}
}
You want to look at using something like Enum.GetValues
#Html.DropDownListFor(model => model.Type, Enum.GetNames(typeof(Rewards.Models.PropertyType)).Select(e => new SelectListItem { Text = e }))
Now this feature is supported out-of-the-box in MVC 5.1 through #Html.EnumDropDownListFor()
Check the following link:
https://learn.microsoft.com/en-us/aspnet/mvc/overview/releases/mvc51-release-notes#Enum
It is really shame that it took Microsoft 5 years to implement such as feature which is so in demand according to the voting above!
This is Rune & Prise answers altered to use the Enum int value as the ID.
Sample Enum:
public enum ItemTypes
{
Movie = 1,
Game = 2,
Book = 3
}
Extension method:
public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
{
var values = from TEnum e in Enum.GetValues(typeof(TEnum))
select new { Id = (int)Enum.Parse(typeof(TEnum), e.ToString()), Name = e.ToString() };
return new SelectList(values, "Id", "Name", (int)Enum.Parse(typeof(TEnum), enumObj.ToString()));
}
Sample of usage:
<%= Html.DropDownList("MyEnumList", ItemTypes.Game.ToSelectList()) %>
Remember to Import the namespace containing the Extension method
<%# Import Namespace="MyNamespace.LocationOfExtensionMethod" %>
Sample of generated HTML:
<select id="MyEnumList" name="MyEnumList">
<option value="1">Movie</option>
<option selected="selected" value="2">Game</option>
<option value="3">Book </option>
</select>
Note that the item that you use to call the ToSelectList on is the selected item.
This is version for Razor:
#{
var itemTypesList = new List<SelectListItem>();
itemTypesList.AddRange(Enum.GetValues(typeof(ItemTypes)).Cast<ItemTypes>().Select(
(item, index) => new SelectListItem
{
Text = item.ToString(),
Value = (index).ToString(),
Selected = Model.ItemTypeId == index
}).ToList());
}
#Html.DropDownList("ItemTypeId", itemTypesList)
Building on Simon's answer, a similar approach is to get the Enum values to display from a Resource file, instead of in a description attribute within the Enum itself. This is helpful if your site needs to be rendered in more than one language and if you were to have a specific resource file for Enums, you could go one step further and have just Enum values, in your Enum and reference them from the extension by a convention such as [EnumName]_[EnumValue] - ultimately less typing!
The extension then looks like:
public static IHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> html, Expression<Func<TModel, TEnum>> expression)
{
var metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);
var enumType = Nullable.GetUnderlyingType(metadata.ModelType) ?? metadata.ModelType;
var enumValues = Enum.GetValues(enumType).Cast<object>();
var items = from enumValue in enumValues
select new SelectListItem
{
Text = GetResourceValueForEnumValue(enumValue),
Value = ((int)enumValue).ToString(),
Selected = enumValue.Equals(metadata.Model)
};
return html.DropDownListFor(expression, items, string.Empty, null);
}
private static string GetResourceValueForEnumValue<TEnum>(TEnum enumValue)
{
var key = string.Format("{0}_{1}", enumValue.GetType().Name, enumValue);
return Enums.ResourceManager.GetString(key) ?? enumValue.ToString();
}
Resources in the Enums.Resx file looking like
ItemTypes_Movie : Film
One other thing I like to do is, instead of calling the extension method directly, I'd rather call it with a #Html.EditorFor(x => x.MyProperty), or ideally just have the whole form, in one neat #Html.EditorForModel(). To do this I change the string template to look like this
#using MVCProject.Extensions
#{
var type = Nullable.GetUnderlyingType(ViewData.ModelMetadata.ModelType) ?? ViewData.ModelMetadata.ModelType;
#(typeof (Enum).IsAssignableFrom(type) ? Html.EnumDropDownListFor(x => x) : Html.TextBoxFor(x => x))
}
If this interests you, I've put a much more detailed answer here on my blog:
http://paulthecyclist.com/2013/05/24/enum-dropdown/
Well I'm really late to the party, but for what it is worth, I have blogged about this very subject whereby I create a EnumHelper class that enables very easy transformation.
http://jnye.co/Posts/4/creating-a-dropdown-list-from-an-enum-in-mvc-and-c%23
In your controller:
//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(MyEnum.MyEnumValue);
In your View:
#Html.DropDownList("DropDownList")
#* OR *#
#Html.DropDownListFor(m => m.Property, ViewBag.DropDownList as SelectList, null)
The helper class:
public static class EnumHelper
{
// Get the value of the description attribute if the
// enum has one, otherwise use the value.
public static string GetDescription<TEnum>(this TEnum value)
{
var fi = value.GetType().GetField(value.ToString());
if (fi != null)
{
var attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attributes.Length > 0)
{
return attributes[0].Description;
}
}
return value.ToString();
}
/// <summary>
/// Build a select list for an enum
/// </summary>
public static SelectList SelectListFor<T>() where T : struct
{
Type t = typeof(T);
return !t.IsEnum ? null
: new SelectList(BuildSelectListItems(t), "Value", "Text");
}
/// <summary>
/// Build a select list for an enum with a particular value selected
/// </summary>
public static SelectList SelectListFor<T>(T selected) where T : struct
{
Type t = typeof(T);
return !t.IsEnum ? null
: new SelectList(BuildSelectListItems(t), "Text", "Value", selected.ToString());
}
private static IEnumerable<SelectListItem> BuildSelectListItems(Type t)
{
return Enum.GetValues(t)
.Cast<Enum>()
.Select(e => new SelectListItem { Value = e.ToString(), Text = e.GetDescription() });
}
}
I am very late on this one but I just found a really cool way to do this with one line of code, if you are happy to add the Unconstrained Melody NuGet package (a nice, small library from Jon Skeet).
This solution is better because:
It ensures (with generic type constraints) that the value really is an enum value (due to Unconstrained Melody)
It avoids unnecessary boxing (due to Unconstrained Melody)
It caches all the descriptions to avoid using reflection on every call (due to Unconstrained Melody)
It is less code than the other solutions!
So, here are the steps to get this working:
In Package Manager Console, "Install-Package UnconstrainedMelody"
Add a property on your model like so:
//Replace "YourEnum" with the type of your enum
public IEnumerable<SelectListItem> AllItems
{
get
{
return Enums.GetValues<YourEnum>().Select(enumValue => new SelectListItem { Value = enumValue.ToString(), Text = enumValue.GetDescription() });
}
}
Now that you have the List of SelectListItem exposed on your model, you can use the #Html.DropDownList or #Html.DropDownListFor using this property as the source.
I found an answer here. However, some of my enums have [Description(...)] attribute, so I've modified the code to provide support for that:
enum Abc
{
[Description("Cba")]
Abc,
Def
}
public static MvcHtmlString EnumDropDownList<TEnum>(this HtmlHelper htmlHelper, string name, TEnum selectedValue)
{
IEnumerable<TEnum> values = Enum.GetValues(typeof(TEnum))
.Cast<TEnum>();
List<SelectListItem> items = new List<SelectListItem>();
foreach (var value in values)
{
string text = value.ToString();
var member = typeof(TEnum).GetMember(value.ToString());
if (member.Count() > 0)
{
var customAttributes = member[0].GetCustomAttributes(typeof(DescriptionAttribute), false);
if (customAttributes.Count() > 0)
{
text = ((DescriptionAttribute)customAttributes[0]).Description;
}
}
items.Add(new SelectListItem
{
Text = text,
Value = value.ToString(),
Selected = (value.Equals(selectedValue))
});
}
return htmlHelper.DropDownList(
name,
items
);
}
Hope that helps.
Another fix to this extension method - the current version didn't select the enum's current value. I fixed the last line:
public static SelectList ToSelectList<TEnum>(this TEnum enumObj) where TEnum : struct
{
if (!typeof(TEnum).IsEnum) throw new ArgumentException("An Enumeration type is required.", "enumObj");
var values = from TEnum e in Enum.GetValues(typeof(TEnum))
select new
{
ID = (int)Enum.Parse(typeof(TEnum), e.ToString()),
Name = e.ToString()
};
return new SelectList(values, "ID", "Name", ((int)Enum.Parse(typeof(TEnum), enumObj.ToString())).ToString());
}
If you want to add localization support just change the s.toString() method to something like this:
ResourceManager rManager = new ResourceManager(typeof(Resources));
var dayTypes = from OperatorCalendarDay.OperatorDayType s in Enum.GetValues(typeof(OperatorCalendarDay.OperatorDayType))
select new { ID = s, Name = rManager.GetString(s.ToString()) };
In here the typeof(Resources) is the resource you want to load, and then you get the localized String, also useful if your enumerator has values with multiple words.
This is my version of helper method.
I use this:
var values = from int e in Enum.GetValues(typeof(TEnum))
select new { ID = e, Name = Enum.GetName(typeof(TEnum), e) };
Instead of that:
var values = from TEnum e in Enum.GetValues(typeof(TEnum))
select new { ID = (int)Enum.Parse(typeof(TEnum),e.ToString())
, Name = e.ToString() };
Here it is:
public static SelectList ToSelectList<TEnum>(this TEnum self) where TEnum : struct
{
if (!typeof(TEnum).IsEnum)
{
throw new ArgumentException("self must be enum", "self");
}
Type t = typeof(TEnum);
var values = from int e in Enum.GetValues(typeof(TEnum))
select new { ID = e, Name = Enum.GetName(typeof(TEnum), e) };
return new SelectList(values, "ID", "Name", self);
}
You can also use my custom HtmlHelpers in Griffin.MvcContrib. The following code:
#Html2.CheckBoxesFor(model => model.InputType) <br />
#Html2.RadioButtonsFor(model => model.InputType) <br />
#Html2.DropdownFor(model => model.InputType) <br />
Generates:
https://github.com/jgauffin/griffin.mvccontrib
#Html.DropdownListFor(model=model->Gender,new List<SelectListItem>
{
new ListItem{Text="Male",Value="Male"},
new ListItem{Text="Female",Value="Female"},
new ListItem{Text="--- Select -----",Value="-----Select ----"}
}
)
I would like to answer this question in a different way where, user need not to do anything in controller or Linq expression. This way...
I have a ENUM
public enum AccessLevelEnum
{
/// <summary>
/// The user cannot access
/// </summary>
[EnumMember, Description("No Access")]
NoAccess = 0x0,
/// <summary>
/// The user can read the entire record in question
/// </summary>
[EnumMember, Description("Read Only")]
ReadOnly = 0x01,
/// <summary>
/// The user can read or write
/// </summary>
[EnumMember, Description("Read / Modify")]
ReadModify = 0x02,
/// <summary>
/// User can create new records, modify and read existing ones
/// </summary>
[EnumMember, Description("Create / Read / Modify")]
CreateReadModify = 0x04,
/// <summary>
/// User can read, write, or delete
/// </summary>
[EnumMember, Description("Create / Read / Modify / Delete")]
CreateReadModifyDelete = 0x08,
/*/// <summary>
/// User can read, write, or delete
/// </summary>
[EnumMember, Description("Create / Read / Modify / Delete / Verify / Edit Capture Value")]
CreateReadModifyDeleteVerify = 0x16*/
}
Now I canto simply create a dropdown by using this enum.
#Html.DropDownList("accessLevel",new SelectList(AccessLevelEnum.GetValues(typeof(AccessLevelEnum))),new { #class = "form-control" })
OR
#Html.DropDownListFor(m=>m.accessLevel,new SelectList(AccessLevelEnum.GetValues(typeof(AccessLevelEnum))),new { #class = "form-control" })
If you want to make a index selected then try this
#Html.DropDownListFor(m=>m.accessLevel,new SelectList(AccessLevelEnum.GetValues(typeof(AccessLevelEnum)) , AccessLevelEnum.NoAccess ),new { #class = "form-control" })
Here I have used AccessLevelEnum.NoAccess as an extra parameter for default selecting the dropdown.
#Simon Goldstone: Thanks for your solution, it can be perfectly applied in my case. The only problem is I had to translate it to VB. But now it is done and to save other people's time (in case they need it) I put it here:
Imports System.Runtime.CompilerServices
Imports System.ComponentModel
Imports System.Linq.Expressions
Public Module HtmlHelpers
Private Function GetNonNullableModelType(modelMetadata As ModelMetadata) As Type
Dim realModelType = modelMetadata.ModelType
Dim underlyingType = Nullable.GetUnderlyingType(realModelType)
If Not underlyingType Is Nothing Then
realModelType = underlyingType
End If
Return realModelType
End Function
Private ReadOnly SingleEmptyItem() As SelectListItem = {New SelectListItem() With {.Text = "", .Value = ""}}
Private Function GetEnumDescription(Of TEnum)(value As TEnum) As String
Dim fi = value.GetType().GetField(value.ToString())
Dim attributes = DirectCast(fi.GetCustomAttributes(GetType(DescriptionAttribute), False), DescriptionAttribute())
If Not attributes Is Nothing AndAlso attributes.Length > 0 Then
Return attributes(0).Description
Else
Return value.ToString()
End If
End Function
<Extension()>
Public Function EnumDropDownListFor(Of TModel, TEnum)(ByVal htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TEnum))) As MvcHtmlString
Return EnumDropDownListFor(htmlHelper, expression, Nothing)
End Function
<Extension()>
Public Function EnumDropDownListFor(Of TModel, TEnum)(ByVal htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TEnum)), htmlAttributes As Object) As MvcHtmlString
Dim metaData As ModelMetadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData)
Dim enumType As Type = GetNonNullableModelType(metaData)
Dim values As IEnumerable(Of TEnum) = [Enum].GetValues(enumType).Cast(Of TEnum)()
Dim items As IEnumerable(Of SelectListItem) = From value In values
Select New SelectListItem With
{
.Text = GetEnumDescription(value),
.Value = value.ToString(),
.Selected = value.Equals(metaData.Model)
}
' If the enum is nullable, add an 'empty' item to the collection
If metaData.IsNullableValueType Then
items = SingleEmptyItem.Concat(items)
End If
Return htmlHelper.DropDownListFor(expression, items, htmlAttributes)
End Function
End Module
End You use it like this:
#Html.EnumDropDownListFor(Function(model) (model.EnumField))
I ended up creating extention methods to do what is essentially the accept answer here. The last half of the Gist deals with Enum specifically.
https://gist.github.com/3813767
#Html.DropDownListFor(model => model.MaritalStatus, new List<SelectListItem>
{
new SelectListItem { Text = "----Select----", Value = "-1" },
new SelectListItem { Text = "Marrid", Value = "M" },
new SelectListItem { Text = "Single", Value = "S" }
})