DropDownList Constructor ()
.NET Framework (current version)
Initializes a new instance of the DropDownList class.
Assembly: System.Web (in System.Web.dll)
Use this constructor to create and initialize a new instance of the DropDownList class.
The following code example demonstrates how to create and initialize a new instance of the DropDownList class.
<%@ 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) { // Retrieve the DropDownList control from the Controls // collection of the PlaceHolder control. DropDownList DropList = (DropDownList)Place.FindControl("ColorList"); // 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(DropList.SelectedItem.Value); } void Page_Load(Object sender, EventArgs e) { // Create a DropDownList control. DropDownList DropList = new DropDownList(); // Set the properties for the DropDownList control. DropList.ID = "ColorList"; DropList.AutoPostBack = true; // Manually register the event-handling method for the // SelectedIndexChanged event. DropList.SelectedIndexChanged += new EventHandler(this.Selection_Change); // Because the DropDownList control is created dynamically each // time the page is loaded, the data must be bound to the // control each time the page is refreshed. // Specify the data source and field names for the Text and // Value properties of the items (ListItem objects) in the // DropDownList control. DropList.DataSource = CreateDataSource(); DropList.DataTextField = "ColorTextField"; DropList.DataValueField = "ColorValueField"; // Bind the data to the control. DropList.DataBind(); // Set the default selected item when the page is first loaded. if(!IsPostBack) { DropList.SelectedIndex = 0; } // Add the DropDownList control to the Controls collection of // the PlaceHolder control. Place.Controls.Add(DropList); } 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 Constructor Example </title> </head> <body> <form id="form1" runat="server"> <h3> DropDownList Constructor 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:PlaceHolder id="Place" runat="server"/> </td> </tr> </table> </form> </body> </html>
.NET Framework
Available since 1.1
Available since 1.1
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