Introduction
Use the DropDownList control to create a single-selection drop-down list control. You can control the appearance of the DropDownList control by setting the BorderColor,BorderStyle, and BorderWidth properties.
To specify the items that you want to appear in the DropDownList control, place a ListItem object for each entry between the opening and closing tags of the DropDownListcontrol.
The DropDownList control also supports data binding. To bind the control to a data source, create a data source, such as a System.Collections.ArrayList object, that contains the items to display in the control. Then, use the Control.DataBind method to bind the data source to the DropDownList control.
Use the SelectedIndex property to programmatically determine the index of the item selected by the user from the DropDownList control. The index can then be used to retrieve the selected item from the Items collection of the control.
The following code example demonstrates how to create a DropDownList control though data binding.
<%@ Page Language="C#" AutoEventWireup="True" %> <%@ Import Namespace="System.Data" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <script runat="server" > void Selection_Change(Object sender, EventArgs e) { // Set the background color for days in the Calendar control // based on the value selected by the user from the // DropDownList control. Calendar1.DayStyle.BackColor = System.Drawing.Color.FromName(ColorList.SelectedItem.Value); } void Page_Load(Object sender, EventArgs e) { // Load data for the DropDownList control only once, when the // page is first loaded. if(!IsPostBack) { // Specify the data source and field names for the Text // and Value properties of the items (ListItem objects) // in the DropDownList control. ColorList.DataSource = CreateDataSource(); ColorList.DataTextField = "ColorTextField"; ColorList.DataValueField = "ColorValueField"; // Bind the data to the control. ColorList.DataBind(); // Set the default selected item, if desired. ColorList.SelectedIndex = 0; } } ICollection CreateDataSource() { // Create a table to store data for the DropDownList control. DataTable dt = new DataTable(); // Define the columns of the table. dt.Columns.Add(new DataColumn("ColorTextField", typeof(String))); dt.Columns.Add(new DataColumn("ColorValueField", typeof(String))); // Populate the table with sample values. dt.Rows.Add(CreateRow("White", "White", dt)); dt.Rows.Add(CreateRow("Silver", "Silver", dt)); dt.Rows.Add(CreateRow("Dark Gray", "DarkGray", dt)); dt.Rows.Add(CreateRow("Khaki", "Khaki", dt)); dt.Rows.Add(CreateRow("Dark Khaki", "DarkKhaki", dt)); // Create a DataView from the DataTable to act as the data source // for the DropDownList control. DataView dv = new DataView(dt); return dv; } DataRow CreateRow(String Text, String Value, DataTable dt) { // Create a DataRow using the DataTable defined in the // CreateDataSource method. DataRow dr = dt.NewRow(); // This DataRow contains the ColorTextField and ColorValueField // fields, as defined in the CreateDataSource method. Set the // fields with the appropriate value. Remember that column 0 // is defined as ColorTextField, and column 1 is defined as // ColorValueField. dr[0] = Text; dr[1] = Value; return dr; } </script> <head runat="server"> <title> DropDownList Data Binding Example </title> </head> <body> <form id="form1" runat="server"> <h3> DropDownList Data Binding Example </h3> Select a background color for days in the calendar. <br /><br /> <asp:Calendar id="Calendar1" ShowGridLines="True" ShowTitle="True" runat="server"/> <br /><br /> <table cellpadding="5"> <tr> <td> Background color: </td> </tr> <tr> <td> <asp:DropDownList id="ColorList" AutoPostBack="True" OnSelectedIndexChanged="Selection_Change" runat="server"/> </td> </tr> </table> </form> </body> </html>
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