DropDownList Konstruktor
Definition
Wichtig
Einige Informationen beziehen sich auf Vorabversionen, die vor dem Release ggf. grundlegend überarbeitet werden. Microsoft übernimmt hinsichtlich der hier bereitgestellten Informationen keine Gewährleistungen, seien sie ausdrücklich oder konkludent.
Initialisiert eine neue Instanz der DropDownList-Klasse.
public:
DropDownList();
public DropDownList ();
Public Sub New ()
Beispiele
Im folgenden Codebeispiel wird veranschaulicht, wie Sie eine neue Instanz der DropDownList Klasse erstellen und initialisieren.
<%@ 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>
<%@ 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>
Hinweise
Verwenden Sie diesen Konstruktor, um eine neue Instanz der DropDownList Klasse zu erstellen und zu initialisieren.