How can I add option groups in ASP.NET drop down list?

Question

I have a requirement of grouping the drop down list options in ASP.NET drop down server control. Do you have any idea to how to approach the issue? I am new to ASP.NET.

Answer 1

I prefered a client script solution to avoid the complications at postback, so i solved it like this. Here I use an ordinary html select just to show it in function, but it works with ASP DropDownList too:

<script>
function addOptGrp() {
  var t, p
  for (var i = 0; i < arguments.length; i=i+2) {
    t=arguments[i];
    p=arguments[i+1]-i/2;
    var scripts = document.getElementsByTagName('script');
/* On the next line scripts[scripts.length - 1] is the last script 
   in the page, which by definition will always be the calling script, 
   no matter how many such scripts you have */
    var ddl = scripts[scripts.length - 1].previousElementSibling;
    var og = document.createElement("optgroup");
    og.label = t;
    ddl.add(og,p);
    ddl.selectedIndex = ddl.selectedIndex // needed for UI;
  }
}
</script>

<select style="width:100px;">
  <option>Apple</option>
  <option>Pear</option>
  <option>Banana</option>
  <option>Orange</option>
</select>
<!-- here I just add the option groups in a script that immediately executes. 
     Notice that the script must follow immediately after the select (or DropDownList) -->
<script>addOptGrp(
  'Simple fruits', 0,
  'Very exotic fruits', 3
)</script>
<br><br>

<!-- Here comes another one -->
<select style="width:100px;">
  <option>Red</option>
  <option>Blue</option>
  <option>Yellow</option>
  <option>Green</option>
  <option>Magenta</option>
  <option>White</option>
</select>
<script>addOptGrp(
  'Some colors', 0,
  'Some more colors', 4
)</script>

This function fulfilled the needs I had today. Another day one might need to use a modified version, for example where it converts ordinary options to optgroups, depending on some prefix or so.

Answer 2

----- in .cs  -----

List<SelectListItem> sl = new List<SelectListItem>();

sl.Add(new SelectListItem() { Text = "My text", Value = "1", Group = new SelectListGroup() { Name = "First Group" } });

sl.Add(new SelectListItem() { Text = "My text 2", Value = "2", Group = new SelectListGroup() { Name = "First Group" } });

var sl1 = new SelectList(sl,"Value","Text","Group.Name",-1);

ViewData["MyList"] = sl1;


----- in .cshtml    -----
Html.DropDownList("My List", ViewData["MyList"] as SelectList,
                        "-- No Preference --",
                        new {
                            @class = "ui-widget ui-corner-all square_corners searchPageDropdown"
                        }))

Answer 3

1) Add the dropdownlist adapter class from here to your project

2) Add App_Browsers folder to your project(right click on project => Add => Add ASP.NET folder => App_Browsers)

3) Add a browser file into App_Browsers page and add the following code below inside browsers tag.

<browser refID="WebKit"> <controlAdapters> <adapter controlType="System.Web.UI.WebControls.DropDownList" adapterType="YourAdapterClasse'sNameSPace.DropDownListAdapter" /> </controlAdapters> </browser>

refId = WebKit supports chrome and safari browsers

4) Then you can add items to your dropdownlist ListItem item1 = new ListItem("Smith Street", "1"); item1.Attributes["OptionGroup"] = "Darwin";

            ListItem item2 = new ListItem("Mitchel Street", "1");
            item2.Attributes["OptionGroup"] = "Darwin";

            ListItem item3 = new ListItem("Hunter Street", "2");
            item3.Attributes["OptionGroup"] = "Sydney";

            ListItem item4 = new ListItem("BroadwaY", "4");
            item4.Attributes["OptionGroup"] = "Sydney";

            venuedropdown.Items.Add(item1);
            venuedropdown.Items.Add(item2);
            venuedropdown.Items.Add(item3);
            venuedropdown.Items.Add(item4);

Answer 4

I really like this client-side solution (doesn't need a custom DropDownList, but uses jQuery):

backend

private void _addSelectItem(DropDownList list, string title, string value, string group = null) {
   ListItem item = new ListItem(title, value);
   if (!String.IsNullOrEmpty(group))
   {
       item.Attributes["data-category"] = group;
   }
   list.Items.Add(item);
}

...
_addSelectItem(dropDown, "Option 1", "1");
_addSelectItem(dropDown, "Option 2", "2", "Category");
_addSelectItem(dropDown, "Option 3", "3", "Category");
...

client

var groups = {};
$("select option[data-category]").each(function () {
     groups[$.trim($(this).attr("data-category"))] = true;
});
$.each(groups, function (c) {
     $("select option[data-category='"+c+"']").wrapAll('<optgroup label="' + c + '">');
});

Answer 5

Check out this article, I too had need for Group DropDown list . . .

ASP.NET DropDownList with OptionGroup support

Usage :

protected void Page_Load(object sender, EventArgs e) 
{

              ListItem item1 = new ListItem("Camel", "1");
              item1.Attributes["OptionGroup"] = "Mammals";

              ListItem item2 = new ListItem("Lion", "2");
              item2.Attributes["OptionGroup"] = "Mammals";

              ListItem item3 = new ListItem("Whale", "3");
              item3.Attributes["OptionGroup"] = "Mammals";

              ListItem item4 = new ListItem("Walrus", "4");
              item4.Attributes["OptionGroup"] = "Mammals";

              ListItem item5 = new ListItem("Velociraptor", "5");
              item5.Attributes["OptionGroup"] = "Dinosaurs";

              ListItem item6 = new ListItem("Allosaurus", "6");
              item6.Attributes["OptionGroup"] = "Dinosaurs";

              ListItem item7 = new ListItem("Triceratops", "7");
              item7.Attributes["OptionGroup"] = "Dinosaurs";

              ListItem item8 = new ListItem("Stegosaurus", "8");
              item8.Attributes["OptionGroup"] = "Dinosaurs";

              ListItem item9 = new ListItem("Tyrannosaurus", "9");
              item9.Attributes["OptionGroup"] = "Dinosaurs";


              ddlItems.Items.Add(item1);
              ddlItems.Items.Add(item2);
              ddlItems.Items.Add(item3);
              ddlItems.Items.Add(item4);
              ddlItems.Items.Add(item5);
              ddlItems.Items.Add(item6);
              ddlItems.Items.Add(item7);
              ddlItems.Items.Add(item8);
              ddlItems.Items.Add(item9);

          }

Answer 6

This is old but since I used the accepted answer recently I wanted to share my experience with it. While it does provide the correct markup, it caused problems for me, specifically whenever I tried to submit a form with any dropdownlist I would get the dreaded "Invalid postback or callback argument" error. After googling like a maniac, I came across this article which then links to this blog post. The code I ended up using was this:

    public class DropDownListAdapter : System.Web.UI.WebControls.Adapters.WebControlAdapter {
    protected override void RenderContents(HtmlTextWriter writer) {

        var dropDownList = (DropDownList)Control;
        var items = dropDownList.Items;

        var groups = (from p in items.OfType<ListItem>()
                      group p by p.Attributes["Group"] into g
                      select new { Label = g.Key, Items = g.ToList() });

        foreach (var group in groups)
        {
            if (!String.IsNullOrEmpty(group.Label))
            {
                writer.WriteBeginTag("optgroup");
                writer.WriteAttribute("label", group.Label);
                writer.Write(">");
            }

            var count = group.Items.Count();
            if (count > 0)
            {
                var flag = false;
                for (var i = 0; i < count; i++)
                {
                    var item = group.Items[i];

                    writer.WriteBeginTag("option");
                    if (item.Selected)
                    {
                        if (flag)
                        {
                            throw new HttpException("Multiple selected items not allowed");
                        }
                        flag = true;

                        writer.WriteAttribute("selected", "selected");
                    }

                    if (!item.Enabled)
                    {
                        writer.WriteAttribute("disabled", "true");
                    }

                    writer.WriteAttribute("value", item.Value, true);

                    if (Page != null)
                    {
                        Page.ClientScript.RegisterForEventValidation(dropDownList.UniqueID, item.Value);
                    }
                    writer.Write('>');
                    HttpUtility.HtmlEncode(item.Text, writer);
                    writer.WriteEndTag("option");
                    writer.WriteLine();
                }
            }
            if (!String.IsNullOrEmpty(group.Label))
            {
                writer.WriteEndTag("optgroup");
            }
        }
    }
}

The listitems used here are created in the design page rather than the code-behind page like so:

<asp:ListItem Value="apple" Text="Apple" Group="Fruit"></asp:ListItem>
<asp:ListItem Value="banana" Text="Banana" Group="Fruit"></asp:ListItem>
<asp:ListItem Value="asparagus" Text="Asparagus" Group="Vegetable"></asp:ListItem>
<asp:ListItem Value="eggs" Text="Eggs" Group="Dairy"></asp:ListItem>

This produced the same markup as the accepted answer here but this didn't give me the postback error. I hope this saves someone some grief.