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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)

'Declaration
Public Sub New

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="VB" 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" >

      Sub Selection_Change(sender as Object, e As EventArgs)

         ' Retrieve the DropDownList control from the Controls 
         ' collection of the PlaceHolder control.
         Dim DropList As DropDownList = _
             CType(Place.FindControl("ColorList"), DropDownList) 

         ' 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)

      End Sub

      Sub Page_Load(sender as Object, e As EventArgs)

         ' Create a DropDownList control.
         Dim DropList As DropDownList = 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.
         AddHandler DropList.SelectedIndexChanged, AddressOf 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 Not IsPostBack Then

            DropList.SelectedIndex = 0

         End If

         ' Add the DropDownList control to the Controls collection of 
         ' the PlaceHolder control.
         Place.Controls.Add(DropList)

      End Sub

      Function CreateDataSource() As ICollection 

         ' Create a table to store data for the DropDownList control.
         Dim dt As DataTable = New DataTable()

         ' Define the columns of the table.
         dt.Columns.Add(new DataColumn("ColorTextField", GetType(String)))
         dt.Columns.Add(new DataColumn("ColorValueField", GetType(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.
         Dim dv As DataView = New DataView(dt)
         Return dv

      End Function

      Function CreateRow(Text As String, Value As String, dt As DataTable) As DataRow 

         ' Create a DataRow using the DataTable defined in the 
         ' CreateDataSource method.
         Dim dr As DataRow = 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

      End Function

   </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, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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