How do you bind an Enum to a DropDownList control in ASP.NET?

Ray_Vega_4872 0
Viewed 182819

Let's say I have the following simple enum:

enum Response
{
    Yes = 1,
    No = 2,
    Maybe = 3
}

How can I bind this enum to a DropDownList control so that the descriptions are displayed in the list as well as retrieve the associated numeric value (1,2,3) once an option has been selected?

asp.net .net c#
27 Answers

I probably wouldn't bind the data as it's an enum, and it won't change after compile time (unless I'm having one of those stoopid moments).

Better just to iterate through the enum: 

Dim itemValues As Array = System.Enum.GetValues(GetType(Response))
Dim itemNames As Array = System.Enum.GetNames(GetType(Response))

For i As Integer = 0 To itemNames.Length - 1
    Dim item As New ListItem(itemNames(i), itemValues(i))
    dropdownlist.Items.Add(item)
Next

Or the same in C# 

Array itemValues = System.Enum.GetValues(typeof(Response));
Array itemNames = System.Enum.GetNames(typeof(Response));

for (int i = 0; i <= itemNames.Length - 1 ; i++) {
    ListItem item = new ListItem(itemNames[i], itemValues[i]);
    dropdownlist.Items.Add(item);
}
Mark_Glorie_9520

Use the following utility class Enumeration to get an IDictionary<int,string> (Enum value & name pair) from an Enumeration; you then bind the IDictionary to a bindable Control.

public static class Enumeration
{
    public static IDictionary<int, string> GetAll<TEnum>() where TEnum: struct
    {
        var enumerationType = typeof (TEnum);

        if (!enumerationType.IsEnum)
            throw new ArgumentException("Enumeration type is expected.");

        var dictionary = new Dictionary<int, string>();

        foreach (int value in Enum.GetValues(enumerationType))
        {
            var name = Enum.GetName(enumerationType, value);
            dictionary.Add(value, name);
        }

        return dictionary;
    }
}

Example: Using the utility class to bind enumeration data to a control

ddlResponse.DataSource = Enumeration.GetAll<Response>();
ddlResponse.DataTextField = "Value";
ddlResponse.DataValueField = "Key";
ddlResponse.DataBind();
user_33590

I use this for ASP.NET MVC:

Html.DropDownListFor(o => o.EnumProperty, Enum.GetValues(typeof(enumtype)).Cast<enumtype>().Select(x => new SelectListItem { Text = x.ToString(), Value = ((int)x).ToString() }))
user_825390

My version is just a compressed form of the above:

foreach (Response r in Enum.GetValues(typeof(Response)))
{
    ListItem item = new ListItem(Enum.GetName(typeof(Response), r), r.ToString());
    DropDownList1.Items.Add(item);
}
VanOrman_45500 
public enum Color
{
    RED,
    GREEN,
    BLUE
}

Every Enum type derives from System.Enum. There are two static methods that help bind data to a drop-down list control (and retrieve the value). These are Enum.GetNames and Enum.Parse. Using GetNames, you are able to bind to your drop-down list control as follows:

protected System.Web.UI.WebControls.DropDownList ddColor;

private void Page_Load(object sender, System.EventArgs e)
{
     if(!IsPostBack)
     {
        ddColor.DataSource = Enum.GetNames(typeof(Color));
        ddColor.DataBind();
     }
}

Now if you want the Enum value Back on Selection ....

  private void ddColor_SelectedIndexChanged(object sender, System.EventArgs e)
  {
    Color selectedColor = (Color)Enum.Parse(typeof(Color),ddColor.SelectedValue
  }
Admin1

As others have already said - don't databind to an enum, unless you need to bind to different enums depending on situation. There are several ways to do this, a couple of examples below.

ObjectDataSource

A declarative way of doing it with ObjectDataSource. First, create a BusinessObject class that will return the List to bind the DropDownList to:

public class DropDownData
{
    enum Responses { Yes = 1, No = 2, Maybe = 3 }

    public String Text { get; set; }
    public int Value { get; set; }

    public List<DropDownData> GetList()
    {
        var items = new List<DropDownData>();
        foreach (int value in Enum.GetValues(typeof(Responses)))
        {
            items.Add(new DropDownData
                          {
                              Text = Enum.GetName(typeof (Responses), value),
                              Value = value
                          });
        }
        return items;
    }
}

Then add some HTML markup to the ASPX page to point to this BO class:

<asp:DropDownList ID="DropDownList1" runat="server" 
    DataSourceID="ObjectDataSource1" DataTextField="Text" DataValueField="Value">
</asp:DropDownList>
<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" 
    SelectMethod="GetList" TypeName="DropDownData"></asp:ObjectDataSource>

This option requires no code behind.

Code Behind DataBind

To minimize the HTML in the ASPX page and do bind in Code Behind:

enum Responses { Yes = 1, No = 2, Maybe = 3 }

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        foreach (int value in Enum.GetValues(typeof(Responses)))
        {
            DropDownList1.Items.Add(new ListItem(Enum.GetName(typeof(Responses), value), value.ToString()));
        }
    }
}

Anyway, the trick is to let the Enum type methods of GetValues, GetNames etc. to do work for you.

user_64150

I am not sure how to do it in ASP.NET but check out this post... it might help?

Enum.GetValues(typeof(Response));
rudigrobler_51470 
Array itemValues = Enum.GetValues(typeof(TaskStatus));
Array itemNames = Enum.GetNames(typeof(TaskStatus));

for (int i = 0; i <= itemNames.Length; i++)
{
    ListItem item = new ListItem(itemNames.GetValue(i).ToString(),
    itemValues.GetValue(i).ToString());
    ddlStatus.Items.Add(item);
}
Admin1

Generic Code Using Answer six.

public static void BindControlToEnum(DataBoundControl ControlToBind, Type type)
{
    //ListControl

    if (type == null)
        throw new ArgumentNullException("type");
    else if (ControlToBind==null )
        throw new ArgumentNullException("ControlToBind");
    if (!type.IsEnum)
        throw new ArgumentException("Only enumeration type is expected.");

    Dictionary<int, string> pairs = new Dictionary<int, string>();

    foreach (int i in Enum.GetValues(type))
    {
        pairs.Add(i, Enum.GetName(type, i));
    }
    ControlToBind.DataSource = pairs;
    ListControl lstControl = ControlToBind as ListControl;
    if (lstControl != null)
    {
        lstControl.DataTextField = "Value";
        lstControl.DataValueField = "Key";
    }
    ControlToBind.DataBind();

}
user_2525160
roman_36610

You could also use Extension methods. For those not familar with extensions I suggest checking the VB and C# documentation.

VB Extension:

Namespace CustomExtensions
    Public Module ListItemCollectionExtension

        <Runtime.CompilerServices.Extension()> _
        Public Sub AddEnum(Of TEnum As Structure)(items As System.Web.UI.WebControls.ListItemCollection)
            Dim enumerationType As System.Type = GetType(TEnum)
            Dim enumUnderType As System.Type = System.Enum.GetUnderlyingType(enumType)

            If Not enumerationType.IsEnum Then Throw New ArgumentException("Enumeration type is expected.")

            Dim enumTypeNames() As String = System.Enum.GetNames(enumerationType)
            Dim enumTypeValues() As TEnum = System.Enum.GetValues(enumerationType)

            For i = 0 To enumTypeNames.Length - 1
                items.Add(New System.Web.UI.WebControls.ListItem(saveResponseTypeNames(i), TryCast(enumTypeValues(i), System.Enum).ToString("d")))
            Next
        End Sub
    End Module
End Namespace

To use the extension:

Imports <projectName>.CustomExtensions.ListItemCollectionExtension

...

yourDropDownList.Items.AddEnum(Of EnumType)()

C# Extension:

namespace CustomExtensions
{
    public static class ListItemCollectionExtension
    {
        public static void AddEnum<TEnum>(this System.Web.UI.WebControls.ListItemCollection items) where TEnum : struct
        {
            System.Type enumType = typeof(TEnum);
            System.Type enumUnderType = System.Enum.GetUnderlyingType(enumType);

            if (!enumType.IsEnum) throw new Exception("Enumeration type is expected.");

            string[] enumTypeNames = System.Enum.GetNames(enumType);
            TEnum[] enumTypeValues = (TEnum[])System.Enum.GetValues(enumType);

            for (int i = 0; i < enumTypeValues.Length; i++)
            {
                items.add(new System.Web.UI.WebControls.ListItem(enumTypeNames[i], (enumTypeValues[i] as System.Enum).ToString("d")));
            }
        }
    }
}

To use the extension:

using CustomExtensions.ListItemCollectionExtension;

...

yourDropDownList.Items.AddEnum<EnumType>()

If you want to set the selected item at the same time replace

items.Add(New System.Web.UI.WebControls.ListItem(saveResponseTypeNames(i), saveResponseTypeValues(i).ToString("d")))

with

Dim newListItem As System.Web.UI.WebControls.ListItem
newListItem = New System.Web.UI.WebControls.ListItem(enumTypeNames(i), Convert.ChangeType(enumTypeValues(i), enumUnderType).ToString())
newListItem.Selected = If(EqualityComparer(Of TEnum).Default.Equals(selected, saveResponseTypeValues(i)), True, False)
items.Add(newListItem)

By converting to System.Enum rather then int size and output issues are avoided. For example 0xFFFF0000 would be 4294901760 as an uint but would be -65536 as an int.

TryCast and as System.Enum are slightly faster than Convert.ChangeType(enumTypeValues[i], enumUnderType).ToString() (12:13 in my speed tests).

user_6418330

You can do this a lot shorter

public enum Test
    {
        Test1 = 1,
        Test2 = 2,
        Test3 = 3
    }
    class Program
    {
        static void Main(string[] args)
        {

            var items = Enum.GetValues(typeof(Test));

            foreach (var item in items)
            {
                //Gives you the names
                Console.WriteLine(item);
            }


            foreach(var item in (Test[])items)
            {
                // Gives you the numbers
                Console.WriteLine((int)item);
            }
        }
    }
user_118463630

For those of us that want a working C# solution that works with any drop and enum...

private void LoadConsciousnessDrop()
{
    string sel_val = this.drp_Consciousness.SelectedValue;
    this.drp_Consciousness.Items.Clear();
    string[] names = Enum.GetNames(typeof(Consciousness));
    
    for (int i = 0; i < names.Length; i++)
        this.drp_Consciousness.Items.Add(new ListItem(names[i], ((int)((Consciousness)Enum.Parse(typeof(Consciousness), names[i]))).ToString()));

    this.drp_Consciousness.SelectedValue = String.IsNullOrWhiteSpace(sel_val) ? null : sel_val;
}
user_15836490

I realize this post is older and for Asp.net, but I wanted to provide a solution I used recently for a c# Windows Forms Project. The idea is to build a dictionary where the keys are the names of the Enumerated elements and the values are the Enumerated values. You then bind the dictionary to the combobox. See a generic function that takes a ComboBox and Enum Type as arguments.

    private void BuildComboBoxFromEnum(ComboBox box, Type enumType) {
        var dict = new Dictionary<string, int>();
        foreach (var foo in Enum.GetValues(enumType)) {
            dict.Add(foo.ToString(), (int)foo);
        }
        box.DropDownStyle = ComboBoxStyle.DropDownList; // Forces comboBox to ReadOnly
        box.DataSource = new BindingSource(dict, null);
        box.DisplayMember = "Key";
        box.ValueMember = "Value";
        // Register a callback that prints the Name and Value of the 
        // selected enum. This should be removed after initial testing.
        box.SelectedIndexChanged += (o, e) => {
            Console.WriteLine("{0} {1}", box.Text, box.SelectedValue);
        };
    }

This function can be used as follows:

BuildComboBoxFromEnum(comboBox1,typeof(Response));
user_30374890

In ASP.NET Core you can use the following Html helper (comes from Microsoft.AspNetCore.Mvc.Rendering):

<select asp-items="Html.GetEnumSelectList<GridReportingStatusFilters>()">
     <option value=""></option>
</select>
user_14913880
Related