DropDown is very similar to how select works in HTML. You can create a dropdown menu with multiple options, and the user can select one of them, with an automatic popup.

I would advise to not write the semantic html select tag with option tags, since I’ve found that to break very easily.

Different from TextEntry, DropDown’s Value property is an object type, since it can hold any type of value and not just a string. You can use the Value:bind attribute to bind the selected value to a variable in your code like Value:bind=@selectedOption.

Options on the DropDown is the list of options that will be displayed in the dropdown menu. It uses its own type called Option - Sandbox.UI.Option. Check the source code for more details.

In one of my use cases, I have a list of players:

private List<Option> Players => BraxnetPlayer.All.Select( x => new Option
	{
		Title = x.DisplayName, Value = x.SteamId.ToString()
	} ).ToList();

private string selectedPlayer { get; set; }

You can see that I create a list of Option objects, where each option has a Title (the text displayed in the dropdown) and a Value (the actual value associated with that option).

Then, in the UI, I can use the DropDown component like this:

<DropDown Options=@Players Value:bind=@selectedPlayer />

You can use ValueChanged to execute some code when the selected value changes:

<DropDown Options=@Players Value:bind=@selectedPlayer ValueChanged=@OnPlayerChanged />

private void OnPlayerChanged(string newPlayer)
{
    // Handle the player change
}

Use Value to set the initial selected value:

<DropDown Options=@Players Value=@selectedPlayer />

The Selected property gives you the currently selected Option object, which can be useful if you need to access more details about the selected option.