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 use this method, which avoids ViewBag and ViewData:

View model:

public class PageViewModel
{
    public int SelectedDropdownItem { get; set; }
    public IEnumerable DropdownList { get; set; }
}

Example entity model (for this example):

public class Users
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsAdministrator { get; set; }
    public bool IsDefault { get; set; }
}

Controller:

// Get list for the dropdown (this uses db values)
var userList = db.Users.ToList();

// Define the Groups
var group1 = new SelectListGroup { Name = "Administrators" };
var group2 = new SelectListGroup { Name = "Users" };

// Note - the -1 is needed at the end of this - pre-selected value is determined further down
// Note .OrderBy() determines the order in which the groups are displayed in the dropdown
var dropdownList = new SelectList(userList.Select(item => new SelectListItem
{
    Text = item.Name,
    Value = item.Id,
    // Assign the Group to the item by some appropriate selection method
    Group = item.IsAdministrator ? group1 : group2
}).OrderBy(a => a.Group.Name).ToList(), "Value", "Text", "Group.Name", -1);

// Assign values to ViewModel
var viewModel = new PageViewModel
{
    // Assign the pre-selected dropdown value by appropriate selction method (if needed)
    SelectedDropdownItem = userList.FirstOrDefault(a => a.IsDefault).Id,
    DropdownList =  dropdownList
};

View:

@Html.DropDownListFor(a => a.SelectedDropdownItem, Model.DropdownList, null, new { @class = "some-class" })

Hope this helps someone to avoid what happened to me - way too much time spent finding a strongly-typed method.