PersistChildrenAttribute Classe

Definição

public ref class PersistChildrenAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Class)]
public sealed class PersistChildrenAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Class)>]
type PersistChildrenAttribute = class
    inherit Attribute

Public NotInheritable Class PersistChildrenAttribute
Inherits Attribute

Herança

Object

Attribute

PersistChildrenAttribute

Atributos

AttributeUsageAttribute

Exemplos

O exemplo de código nesta secção contém duas partes. O primeiro exemplo de código demonstra como definir os metadados de um controlo personalizado para que, no momento do design, o seu conteúdo aninhado seja mantido como propriedades do controlo. O segundo exemplo de código demonstra como usar classes numa página ASP.NET.

O exemplo de código seguinte demonstra como aplicar o PersistChildrenAttribute atributo de modo a que nenhum dos controlos aninhados de um controlo de servidor personalizado seja mantido como controlo aninhado. O controlo personalizado do servidor nomeado CollectionPropertyControl tem o PersistChildrenAttribute atributo definido para false que os Employee objetos adicionados sejam mantidos como elementos aninhados.

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);
      }
   }
}

' 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.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

    
   Public Sub New(name As String, title As String, employeeAlias As String)
      Me._name = name
      Me._title = title
      Me._alias = employeeAlias
   End Sub
   
   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

 ' 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
 End Class
End Namespace ' PersistChildrenSampleVB

O exemplo de código seguinte demonstra como usar as classes CollectionPropertyControl e Employee numa página ASP.NET.

<%@ 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 xmlns="http://www.w3.org/1999/xhtml" >
<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>

<%@ 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 xmlns="http://www.w3.org/1999/xhtml" >
<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>

Observações

O PersistChildrenAttribute é usado em combinação com o ParseChildrenAttribute para determinar como o conteúdo aninhado de um controlo é interpretado. Se PersistChildrenAttribute for true e ParseChildrenAttribute for false, o conteúdo aninhado contido num controlo de servidor ASP.NET é mantido como controlo. Se PersistChildrenAttribute for false e ParseChildrenAttribute for true, o conteúdo aninhado é mantido como propriedades do controlo do servidor. Para mais informações sobre o uso de atributos, consulte Atributos.

Ver também

• Attribute
• ParseChildrenAttribute
• Extensão dos Metadados Usando Atributos
• ArquiteturaDesign-Time