The code example in this section contains two parts. The first code example demonstrates how to set the metadata of a custom control so that at design time, its nested content is persisted as properties of the control. The second code example demonstrates how to use classes in an ASP.NET page.
The following code example demonstrates how to apply the PersistChildrenAttribute attribute so that none of a custom server control's nested controls are persisted as nested controls. The custom server control named CollectionPropertyControl has the PersistChildrenAttribute attribute set to false so that the Employee objects that are added are persisted as nested elements.
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' Create a namespace that defines two classes, one a custom control, Employee,
' which is created for every instance of a child element with its name
' declared in a page associated with this namespace, the other, Employees,
' which contains these child elements.
Imports System
Imports System.Collections
Imports System.Drawing
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Security.Permissions
Namespace PersistChildrenSampleVB
' Create a class that will be rendered as a child of the control
' that has the ParseChildren attribute applied to it.
<AspNetHostingPermission(SecurityAction.Demand, _
Level:=AspNetHostingPermissionLevel.Minimal)> _
Public NotInheritable Class Employee
Private _name As String
Private _title As String
Private _alias As String
Public Sub New()
Me.New("", "", "")
End Sub 'New
Public Sub New(name As String, title As String, employeeAlias As String)
Me._name = name
Me._title = title
Me._alias = employeeAlias
End Sub 'New
Public Property Name() As String
Get
Return _name
End Get
Set
_name = value
End Set
End Property
Public Property Title() As String
Get
Return _title
End Get
Set
_title = value
End Set
End Property
Public Property [Alias]() As String
Get
Return _alias
End Get
Set
_alias = value
End Set
End Property
End Class 'Employee
' Use the PersistChildren attribute to set the Persist
' property to false so that none of this class's
' child controls will be persisted as controls. They will
' be persisted only as child elements of this class.
' If you set the PersistChildren attribute to true, or if you
' do not include this attribute when you create a control,
' the child controls will be persisted as controls.
<PersistChildren(False)> _
<AspNetHostingPermission(SecurityAction.Demand, _
Level:=AspNetHostingPermissionLevel.Minimal)> _
Public NotInheritable Class CollectionPropertyControl
Inherits Control
Private _header As String
Private _employees As New ArrayList()
Public Property Header() As String
Get
Return _header
End Get
Set
_header = value
End Set
End Property
Public ReadOnly Property Employees() As ArrayList
Get
Return _employees
End Get
End Property
' Override the CreateChildControls method to
' add child controls to the Employees property when this
' custom control is requested from a page.
Protected Overrides Sub CreateChildControls()
Dim label As New Label()
label.Text = Header
label.BackColor = Color.Beige
label.ForeColor = Color.Red
Controls.Add(label)
Controls.Add(New LiteralControl("<BR> <BR>"))
Dim table As New Table()
Dim htr As New TableRow()
Dim hcell1 As New TableHeaderCell()
hcell1.Text = "Name"
htr.Cells.Add(hcell1)
Dim hcell2 As New TableHeaderCell()
hcell2.Text = "Title"
htr.Cells.Add(hcell2)
Dim hcell3 As New TableHeaderCell()
hcell3.Text = "Alias"
htr.Cells.Add(hcell3)
table.Rows.Add(htr)
table.BorderWidth = Unit.Pixel(2)
table.BackColor = Color.Beige
table.ForeColor = Color.Red
Dim employee As Employee
For Each employee In Employees
Dim tr As New TableRow()
Dim cell1 As New TableCell()
cell1.Text = employee.Name
tr.Cells.Add(cell1)
Dim cell2 As New TableCell()
cell2.Text = employee.Title
tr.Cells.Add(cell2)
Dim cell3 As New TableCell()
cell3.Text = employee.Alias
tr.Cells.Add(cell3)
table.Rows.Add(tr)
Next employee
Controls.Add(table)
End Sub 'CreateChildControls
End Class 'CollectionPropertyControl
End Namespace ' PersistChildrenSampleVB
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using System;
using System.Collections;
using System.Drawing;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Security.Permissions;
namespace PersistChildrenSamples
{
// The child element class.
[AspNetHostingPermission(SecurityAction.Demand,
Level=AspNetHostingPermissionLevel.Minimal)]
public sealed class Employee
{
private String name;
private String title;
private String alias;
public Employee():this ("","",""){}
public Employee (String name, String title, String alias)
{
this.name = name;
this.title = title;
this.alias = alias;
}
public String Name
{
get
{
return name;
}
set
{
name = value;
}
}
public String Title
{
get
{
return title;
}
set
{
title = value;
}
}
public String Alias
{
get
{
return alias;
}
set
{
alias = value;
}
}
}
// Use the PersistChildren attribute to set the Persist
// property to false so that none of this class's
// child controls will be persisted as controls. They will
// be persisted only as child elements of this class.
// If you set the PersistChildren attribute to true, or if you
// do not include this attribute when you create a control,
// the child controls will be persisted as controls.
[PersistChildren(false)]
[AspNetHostingPermission(SecurityAction.Demand,
Level=AspNetHostingPermissionLevel.Minimal)]
public sealed class CollectionPropertyControl : Control
{
private String header;
private ArrayList employees = new ArrayList();
public String Header
{
get
{
return header;
}
set
{
header = value;
}
}
public ArrayList Employees
{
get
{
return employees;
}
}
// Override the CreateChildControls method to
// add child controls to the Employees property when this
// custom control is requested from a page.
protected override void CreateChildControls()
{
Label label = new Label();
label.Text = Header;
label.BackColor = Color.Beige;
label.ForeColor = Color.Red;
Controls.Add(label);
Controls.Add(new LiteralControl("<BR> <BR>"));
Table table = new Table();
TableRow htr = new TableRow();
TableHeaderCell hcell1 = new TableHeaderCell();
hcell1.Text = "Name";
htr.Cells.Add(hcell1);
TableHeaderCell hcell2 = new TableHeaderCell();
hcell2.Text = "Title";
htr.Cells.Add(hcell2);
TableHeaderCell hcell3 = new TableHeaderCell();
hcell3.Text = "Alias";
htr.Cells.Add(hcell3);
table.Rows.Add(htr);
table.BorderWidth = 2;
table.BackColor = Color.Beige;
table.ForeColor = Color.Red;
foreach (Employee employee in Employees)
{
TableRow tr = new TableRow();
TableCell cell1 = new TableCell();
cell1.Text = employee.Name;
tr.Cells.Add(cell1);
TableCell cell2 = new TableCell();
cell2.Text = employee.Title;
tr.Cells.Add(cell2);
TableCell cell3 = new TableCell();
cell3.Text = employee.Alias;
tr.Cells.Add(cell3);
table.Rows.Add(tr);
}
Controls.Add(table);
}
}
}
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The following code example demonstrates how to use the CollectionPropertyControl and Employee classes in an ASP.NET page.
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<%@ Page Language="VB" %>
<%@ Register TagPrefix="AspSample" Assembly="Samples.AspNet.VB.Controls" Namespace="PersistChildrenSampleVB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
' Create two new employees and add them to the custom control.
Dim e1 As New Employee("Employee 1", "Title 1", "Alias 1")
Dim e2 As New Employee("Employee 2", "Title 2", "Alias 2")
CollectionPropertyControl1.Employees.Add(e1)
CollectionPropertyControl1.Employees.Add(e2)
' Verify attribute values.
Dim p As PersistChildrenAttribute = _
Attribute.GetCustomAttribute(GetType(CollectionPropertyControl), _
GetType(PersistChildrenAttribute))
Dim sb As New StringBuilder()
sb.Append("The Persist property is " & p.Persist.ToString() & "<br />")
sb.Append("The UseCustomPersistence property is " & p.UsesCustomPersistence.ToString() & "<br />")
sb.Append("The IsDefault method returns " & p.IsDefaultAttribute().ToString())
Message.Text = sb.ToString()
End Sub
</script>
<html >
<head id="Head1" runat="server">
<title>PersistChildrenAttribute</title>
</head>
<body>
<form id="Form1" runat="server">
<div>
<asp:Label ID="Message"
runat="server"/>
<AspSample:CollectionPropertyControl id="CollectionPropertyControl1"
runat="server">
</AspSample:CollectionPropertyControl>
</div>
</form>
</body>
</html>
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<%@ Page Language="C#" %>
<%@ Register TagPrefix="AspSample" Assembly="Samples.AspNet.CS.Controls" Namespace="PersistChildrenSamples" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
// Create two new employees and add them to the custom control.
Employee e1 = new Employee("Employee 1", "Title 1", "Alias 1");
Employee e2 = new Employee("Employee 2", "Title 2", "Alias 2");
CollectionPropertyControl1.Employees.Add(e1);
CollectionPropertyControl1.Employees.Add(e2);
// Verify attribute values.
PersistChildrenAttribute p =
(PersistChildrenAttribute)Attribute.GetCustomAttribute(typeof(CollectionPropertyControl),
typeof(PersistChildrenAttribute));
StringBuilder sb = new StringBuilder();
sb.Append("The Persist property is " + p.Persist.ToString() + "<br />");
sb.Append("The UseCustomPersistence property is " + p.UsesCustomPersistence.ToString() + "<br />");
sb.Append("The IsDefault method returns " + p.IsDefaultAttribute().ToString());
Message.Text = sb.ToString();
}
</script>
<html >
<head runat="server">
<title>PersistChildrenAttribute</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Label ID="Message"
runat="server"/>
<AspSample:CollectionPropertyControl id="CollectionPropertyControl1"
runat="server">
</AspSample:CollectionPropertyControl>
</div>
</form>
</body>
</html>
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