Can we validate a DropDownList by RequiredFieldValidator?

Yes, we can validate a DropDownList by RequiredFieldValidator.

Can a DropDownList fire validation controls?

Yes, a DropDownList control can fire validation control when the CausesValidation property of that validation control is set to true and the AutoPostBack property is set to true.

Difference between DropDownList and ListBox in ASP.NET

The basic difference between DropDownList and ListBox in ASP.NET are following

  1. Only one items of DropDownList is visible when it renders on the page. More than one item of the ListBox is visible when it renders on the page.
  2. Only one item can be selected in DropDownList. More than one item can be selected in Listbox provided SelectionMode is Multiple as in the below code snippets.

Both controls are rendered as “<select>” html tag in the HTML.

DROPDOWNLIST

<asp:DropDownList ID="drop1" runat="server">

<asp:ListItem Text="One" Value="1" />

<asp:ListItem Text="Two" Value="2" />

</asp:DropDownList>

LIST BOX

<asp:ListBox ID="list1" runat="server" SelectionMode="Multiple">

<asp:ListItem Text="One" Value="1" />

<asp:ListItem Text="Two" Value="2" />

</asp:ListBox>

What is the difference between ListBox (Filled with data) and DropDownList (Filled with data), in terms of SelectedIndex property?

The default value of the SelectedIndex property of the Listbox is -1, which indicates that no item is selected in the Listbox. However, the DropDownList control overrides this property and sets the default value to 0, which indicates the first item in the list.

How to copy items from one DropDownList control to another DropDownList control?

Write following coder

 foreach (ListItem item in drop1.Items)

        {

            drop2.Items.Add(item);

        }