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DropDownList Constructor

Initializes a new instance of the DropDownList class.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)
public DropDownList()

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

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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