.NET Framework Class Library Parameter Class Provides a mechanism that data source controls use to bind to application variables, user identities and choices, and other data. Serves as the base class for all ASP.NET parameter types.
Inheritance Hierarchy
Namespace:
System.Web.UI.WebControls
Assembly:
System.Web (in System.Web.dll)
Syntax
Public Class Parameter _
Implements ICloneable, IStateManager
public class Parameter : ICloneable, IStateManager
public ref class Parameter : ICloneable,
IStateManager
type Parameter =
class
interface ICloneable
interface IStateManager
end
The Parameter type exposes the following members.
Constructors
|
| Name | Description |
|---|
.gif) | Parameter()()() | Initializes a new default instance of the Parameter class. | .gif) | Parameter(Parameter) | Initializes a new instance of the Parameter class with the values of the original, specified instance. | | Parameter(String) | Initializes a new instance of the Parameter class, using the specified name. | | Parameter(String, DbType) | Initializes a new instance of the Parameter class, using the specified name and database type. | | Parameter(String, TypeCode) | Initializes a new instance of the Parameter class, using the specified name and type. | | Parameter(String, DbType, String) | Initializes a new instance of the Parameter class, using the specified name, the specified database type, and the specified value for its DefaultValue property. | | Parameter(String, TypeCode, String) | Initializes a new instance of the Parameter class, using the specified name, the specified type, and the specified string for its DefaultValue property. |
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Methods
Explicit Interface Implementations
Remarks
The Parameter class represents a parameter in a parameterized SQL query, a filtering expression, or a business object method call that an ASP.NET data source control uses to select, filter, or modify data. Parameter objects are contained in a ParameterCollection object. Parameter objects are evaluated at run time, to bind the values of the variables they represent to whatever method is used by a data source control to interact with data. Use classes that derive from Parameter with data source and data-bound controls to build Web-based data applications. These parameter classes are used by data source controls to bind specific kinds of values found in Web applications to placeholders in SQL query strings, business object method parameters, and more. The following table lists parameter types that are included in ASP.NET. Extend the base Parameter class when you want to implement your own custom parameter types.
Parameter objects are very simple: they have a Name and a Type property, can be represented declaratively, and can track state across multiple HTTP requests. All parameters support a DefaultValue property, for cases when a parameter is bound to a value, but the value evaluates to nullNothingnullptra null reference (Nothing in Visual Basic) at run time. When using a collection of Parameter objects with a data source control, their order in the collection might matter. For more information on how parameters are used, see Using Parameters with the SqlDataSource Control and Using Parameters with the ObjectDataSource Control.
Examples
The following example shows how to use the selected value of a DropDownList control in the Where clause of a SQL query. The example uses the ControlParameter class, which derives from the ControlParameter class. The SelectCommand element defines the query with a parameter named "@Title" where the value from DropDownList1 should go. The ControlParameter element specifies that the "@Title" placeholder will be replaced by the value of the SelectedValue property of the DropDownList1 control. The ControlParameter element is added to the SelectParameters collection of the SqlDataSource control.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<p><asp:dropdownlist
id="DropDownList1"
runat="server"
autopostback="True">
<asp:listitem selected="True">Sales Representative</asp:listitem>
<asp:listitem>Sales Manager</asp:listitem>
<asp:listitem>Vice President, Sales</asp:listitem>
</asp:dropdownlist></p>
<asp:sqldatasource
id="SqlDataSource1"
runat="server"
connectionstring="<%$ ConnectionStrings:MyNorthwind%>"
selectcommand="SELECT LastName FROM Employees WHERE Title = @Title">
<selectparameters>
<asp:controlparameter name="Title" controlid="DropDownList1" propertyname="SelectedValue"/>
</selectparameters>
</asp:sqldatasource>
<p><asp:listbox
id="ListBox1"
runat="server"
datasourceid="SqlDataSource1"
datatextfield="LastName">
</asp:listbox></p>
</form>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<p><asp:dropdownlist
id="DropDownList1"
runat="server"
autopostback="True">
<asp:listitem selected="True">Sales Representative</asp:listitem>
<asp:listitem>Sales Manager</asp:listitem>
<asp:listitem>Vice President, Sales</asp:listitem>
</asp:dropdownlist></p>
<asp:sqldatasource
id="SqlDataSource1"
runat="server"
connectionstring="<%$ ConnectionStrings:MyNorthwind%>"
selectcommand="SELECT LastName FROM Employees WHERE Title = @Title">
<selectparameters>
<asp:controlparameter name="Title" controlid="DropDownList1" propertyname="SelectedValue"/>
</selectparameters>
</asp:sqldatasource>
<p><asp:listbox
id="ListBox1"
runat="server"
datasourceid="SqlDataSource1"
datatextfield="LastName">
</asp:listbox></p>
</form>
</body>
</html>
The following example is like the previous one, but uses code instead of markup. When the page loads the first time, the DropDownList control has no selected value, and the DefaultValue property of the Parameter object is used.
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="param1avb.aspx.vb" Inherits="param1avb_aspx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList
runat="server"
AutoPostBack="True"
id="DropDownList1">
<asp:ListItem Value="USA">USA</asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
</asp:DropDownList>
<asp:DataGrid
runat="server"
id="DataGrid1" />
</div>
</form>
</body>
</html>
<%@ Page Language="C#" CodeFile="param1acs.aspx.cs" Inherits="param1acs_aspx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList
runat="server"
AutoPostBack="True"
id="DropDownList1">
<asp:ListItem Value="USA">USA</asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
</asp:DropDownList>
<asp:DataGrid
runat="server"
id="DataGrid1" />
</div>
</form>
</body>
</html>
The following code shows the code-behind class for the page in the previous example.
Partial Class param1avb_aspx
Inherits System.Web.UI.Page
Private Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Dim sqlSource As SqlDataSource
sqlSource = New SqlDataSource(ConfigurationManager.ConnectionStrings("MyNorthwind").ConnectionString, "SELECT FirstName, LastName FROM Employees WHERE Country = @country;")
Dim country As New ControlParameter()
country.Name = "country"
country.Type = TypeCode.String
country.ControlID = "DropDownList1"
country.PropertyName = "SelectedValue"
' If the DefaultValue is not set, the DataGrid does not
' display anything on the first page load. This is because
' on the first page load, the DropDownList has no
' selected item, and the ControlParameter evaluates to
' String.Empty.
country.DefaultValue = "USA"
sqlSource.SelectParameters.Add(country)
' Add the SqlDataSource to the page controls collection.
Page.Controls.Add(sqlSource)
DataGrid1.DataSource = sqlSource
DataGrid1.DataBind()
End Sub 'Page_Load
End Class
public partial class param1acs_aspx : System.Web.UI.Page
{
private void Page_Load(object sender, System.EventArgs e)
{
SqlDataSource sqlSource = new SqlDataSource(
ConfigurationManager.ConnectionStrings["MyNorthwind"].ConnectionString,
"SELECT FirstName, LastName FROM Employees WHERE Country = @country;");
ControlParameter country = new ControlParameter();
country.Name = "country";
country.Type = TypeCode.String;
country.ControlID = "DropDownList1";
country.PropertyName = "SelectedValue";
// If the DefaultValue is not set, the DataGrid does not
// display anything on the first page load. This is because
// on the first page load, the DropDownList has no
// selected item, and the ControlParameter evaluates to
// String.Empty.
country.DefaultValue = "USA";
sqlSource.SelectParameters.Add(country);
// Add the SqlDataSource to the page controls collection.
Page.Controls.Add(sqlSource);
DataGrid1.DataSource = sqlSource;
DataGrid1.DataBind();
}
}
The following code example demonstrates how to extend the Parameter class to create a new parameter type that can be used by data source controls and other controls in data-binding scenarios. A data source control can use a StaticParameter parameter to bind to the value of any object, typically a string, declared on a Web Forms page.
Imports System
Imports System.ComponentModel
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Namespace Samples.AspNet
<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
Public Class StaticParameter
Inherits Parameter
Public Sub New()
End Sub
' The StaticParameter(string, object) constructor
' initializes the DataValue property and calls the
' Parameter(string) constructor to initialize the Name property.
Public Sub New(name As String, value As Object)
MyBase.New(name)
DataValue = value
End Sub
' The StaticParameter(string, TypeCode, object) constructor
' initializes the DataValue property and calls the
' Parameter(string, TypeCode) constructor to initialize the Name and
' Type properties.
Public Sub New(name As String, type As TypeCode, value As Object)
MyBase.New(name, type)
DataValue = value
End Sub
' The StaticParameter copy constructor is provided to ensure that
' the state contained in the DataValue property is copied to new
' instances of the class.
Protected Sub New(original As StaticParameter)
MyBase.New(original)
DataValue = original.DataValue
End Sub
' The Clone method is overridden to call the
' StaticParameter copy constructor, so that the data in
' the DataValue property is correctly transferred to the
' new instance of the StaticParameter.
Protected Overrides Function Clone() As Parameter
Return New StaticParameter(Me)
End Function
' The DataValue can be any arbitrary object and is stored in ViewState.
Public Property DataValue() As Object
Get
Return ViewState("Value")
End Get
Set
ViewState("Value") = value
End Set
End Property
' The Value property is a type safe convenience property
' used when the StaticParameter represents string data.
' It gets the string value of the DataValue property, and
' sets the DataValue property directly.
Public Property Value() As String
Get
Dim o As Object = DataValue
If o Is Nothing OrElse Not TypeOf o Is String Then
Return String.Empty
End If
Return CStr(o)
End Get
Set
DataValue = value
OnParameterChanged()
End Set
End Property
' The Evaluate method is overridden to return the
' DataValue property instead of the DefaultValue.
Protected Overrides Function Evaluate(context As HttpContext, control As Control) As Object
If context Is Nothing Then
Return Nothing
Else
Return DataValue
End If
End Function
End Class ' StaticParameter
End Namespace ' Samples.AspNet
namespace Samples.AspNet {
using System;
using System.ComponentModel;
using System.Security.Permissions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
[AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
public class StaticParameter : Parameter {
public StaticParameter() {
}
// The StaticParameter(string, object) constructor
// initializes the DataValue property and calls the
// Parameter(string) constructor to initialize the Name property.
public StaticParameter(string name, object value) : base(name) {
DataValue = value;
}
// The StaticParameter(string, TypeCode, object) constructor
// initializes the DataValue property and calls the
// Parameter(string, TypeCode) constructor to initialize the Name and
// Type properties.
public StaticParameter(string name, TypeCode type, object value) : base(name, type) {
DataValue = value;
}
// The StaticParameter copy constructor is provided to ensure that
// the state contained in the DataValue property is copied to new
// instances of the class.
protected StaticParameter(StaticParameter original) : base(original) {
DataValue = original.DataValue;
}
// The Clone method is overridden to call the
// StaticParameter copy constructor, so that the data in
// the DataValue property is correctly transferred to the
// new instance of the StaticParameter.
protected override Parameter Clone() {
return new StaticParameter(this);
}
// The DataValue can be any arbitrary object and is stored in ViewState.
public object DataValue {
get {
return ViewState["Value"];
}
set {
ViewState["Value"] = value;
}
}
// The Value property is a type safe convenience property
// used when the StaticParameter represents string data.
// It gets the string value of the DataValue property, and
// sets the DataValue property directly.
public string Value {
get {
object o = DataValue;
if (o == null || !(o is string))
return String.Empty;
return (string)o;
}
set {
DataValue = value;
OnParameterChanged();
}
}
// The Evaluate method is overridden to return the
// DataValue property instead of the DefaultValue.
protected override object Evaluate(HttpContext context, Control control) {
if (context.Request == null)
return null;
return DataValue;
}
}
}
Version Information
.NET FrameworkSupported in: 4, 3.5, 3.0, 2.0
Platforms
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role not supported), 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.
Thread Safety
Any public static ( Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
See Also
|
Bibliothèque de classes .NET Framework Parameter, classe Fournit un mécanisme que les contrôles de source de données utilisent pour créer une liaison avec les variables d'application, les identités et les choix utilisateur et d'autres données. Sert de classe de base pour tous les types de paramètres ASP.NET.
Hiérarchie d'héritage
Espace de noms :
System.Web.UI.WebControls
Assembly :
System.Web (dans System.Web.dll)
Syntaxe
Public Class Parameter _
Implements ICloneable, IStateManager
public class Parameter : ICloneable, IStateManager
public ref class Parameter : ICloneable,
IStateManager
type Parameter =
class
interface ICloneable
interface IStateManager
end
Le type Parameter expose les membres suivants.
Constructeurs
Méthodes
Notes
La classe Parameter représente un paramètre dans une requête SQL paramétrée, une expression de filtrage ou un appel de méthode d'objet métier utilisé par un contrôle de source de données ASP.NET pour sélectionner, filtrer ou modifier des données. Les objets Parameter sont contenus dans un objet ParameterCollection. Les objets Parameter sont évalués au moment de l'exécution, pour lier les valeurs des variables qu'ils représentent à n'importe quelle méthode utilisée par un contrôle de source de données pour interagir avec les données. Utilisez les classes qui dérivent de Parameter avec les contrôles de source de données et liés aux données pour créer des applications de données Web. Ces classes de paramètres sont utilisées par les contrôles de source de données pour lier les types spécifiques de valeurs présents dans les applications Web aux espaces réservés dans les chaînes de requête SQL, aux paramètres de la méthode de l'objet métier, etc. Le tableau suivant répertorie les types de paramètres inclus dans ASP.NET. Étendez la classe Parameter de base lorsque vous souhaitez implémenter vos propres types de paramètres personnalisés.
Les objets Parameter sont très simples : ils ont un Name et une propriété Type, ils peuvent être représentés de manière déclarative et peuvent effectuer un suivi de l'état à travers plusieurs requêtes HTTP. Tous les paramètres prennent en charge une propriété DefaultValue, dans les cas où un paramètre est lié à une valeur, mais la valeur est nullNothingnullptrune référence null (Nothing en Visual Basic) au moment de l'exécution. Lors de l'utilisation d'une collection d'objets Parameter avec un contrôle de source de données, leur ordre dans la collection peut avoir une importance. Pour plus d'informations sur la façon dont les paramètres sont utilisés, consultez Utilisation de paramètres avec le contrôle SqlDataSource et Utilisation de paramètres avec le contrôle ObjectDataSource.
Exemples
L'exemple suivant montre comment utiliser la valeur sélectionnée d'un contrôle DropDownList dans la clause Where d'une requête SQL. L'exemple utilise la classe ControlParameter dérivée de la classe ControlParameter. L'élément SelectCommand définit la requête avec un paramètre nommé "@Title" où la valeur de DropDownList1 doit être placée. L'élément ControlParameter spécifie que l'espace réservé "@Title" sera remplacé par la valeur de la propriété SelectedValue du contrôle DropDownList1. L'élément ControlParameter est ajouté à la collection SelectParameters du contrôle SqlDataSource.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<p><asp:dropdownlist
id="DropDownList1"
runat="server"
autopostback="True">
<asp:listitem selected="True">Sales Representative</asp:listitem>
<asp:listitem>Sales Manager</asp:listitem>
<asp:listitem>Vice President, Sales</asp:listitem>
</asp:dropdownlist></p>
<asp:sqldatasource
id="SqlDataSource1"
runat="server"
connectionstring="<%$ ConnectionStrings:MyNorthwind%>"
selectcommand="SELECT LastName FROM Employees WHERE Title = @Title">
<selectparameters>
<asp:controlparameter name="Title" controlid="DropDownList1" propertyname="SelectedValue"/>
</selectparameters>
</asp:sqldatasource>
<p><asp:listbox
id="ListBox1"
runat="server"
datasourceid="SqlDataSource1"
datatextfield="LastName">
</asp:listbox></p>
</form>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<p><asp:dropdownlist
id="DropDownList1"
runat="server"
autopostback="True">
<asp:listitem selected="True">Sales Representative</asp:listitem>
<asp:listitem>Sales Manager</asp:listitem>
<asp:listitem>Vice President, Sales</asp:listitem>
</asp:dropdownlist></p>
<asp:sqldatasource
id="SqlDataSource1"
runat="server"
connectionstring="<%$ ConnectionStrings:MyNorthwind%>"
selectcommand="SELECT LastName FROM Employees WHERE Title = @Title">
<selectparameters>
<asp:controlparameter name="Title" controlid="DropDownList1" propertyname="SelectedValue"/>
</selectparameters>
</asp:sqldatasource>
<p><asp:listbox
id="ListBox1"
runat="server"
datasourceid="SqlDataSource1"
datatextfield="LastName">
</asp:listbox></p>
</form>
</body>
</html>
L'exemple suivant est semblable au précédent, mais il utilise le code au lieu du balisage. Lorsque la page se charge pour la première fois, le contrôle DropDownList n'a aucune valeur sélectionnée et la propriété DefaultValue de l'objet Parameter est utilisée.
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="param1avb.aspx.vb" Inherits="param1avb_aspx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList
runat="server"
AutoPostBack="True"
id="DropDownList1">
<asp:ListItem Value="USA">USA</asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
</asp:DropDownList>
<asp:DataGrid
runat="server"
id="DataGrid1" />
</div>
</form>
</body>
</html>
<%@ Page Language="C#" CodeFile="param1acs.aspx.cs" Inherits="param1acs_aspx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<head runat="server">
<title>ASP.NET Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList
runat="server"
AutoPostBack="True"
id="DropDownList1">
<asp:ListItem Value="USA">USA</asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
</asp:DropDownList>
<asp:DataGrid
runat="server"
id="DataGrid1" />
</div>
</form>
</body>
</html>
Le code suivant présente la classe code-behind pour la page dans l'exemple précédent.
Partial Class param1avb_aspx
Inherits System.Web.UI.Page
Private Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Dim sqlSource As SqlDataSource
sqlSource = New SqlDataSource(ConfigurationManager.ConnectionStrings("MyNorthwind").ConnectionString, "SELECT FirstName, LastName FROM Employees WHERE Country = @country;")
Dim country As New ControlParameter()
country.Name = "country"
country.Type = TypeCode.String
country.ControlID = "DropDownList1"
country.PropertyName = "SelectedValue"
' If the DefaultValue is not set, the DataGrid does not
' display anything on the first page load. This is because
' on the first page load, the DropDownList has no
' selected item, and the ControlParameter evaluates to
' String.Empty.
country.DefaultValue = "USA"
sqlSource.SelectParameters.Add(country)
' Add the SqlDataSource to the page controls collection.
Page.Controls.Add(sqlSource)
DataGrid1.DataSource = sqlSource
DataGrid1.DataBind()
End Sub 'Page_Load
End Class
public partial class param1acs_aspx : System.Web.UI.Page
{
private void Page_Load(object sender, System.EventArgs e)
{
SqlDataSource sqlSource = new SqlDataSource(
ConfigurationManager.ConnectionStrings["MyNorthwind"].ConnectionString,
"SELECT FirstName, LastName FROM Employees WHERE Country = @country;");
ControlParameter country = new ControlParameter();
country.Name = "country";
country.Type = TypeCode.String;
country.ControlID = "DropDownList1";
country.PropertyName = "SelectedValue";
// If the DefaultValue is not set, the DataGrid does not
// display anything on the first page load. This is because
// on the first page load, the DropDownList has no
// selected item, and the ControlParameter evaluates to
// String.Empty.
country.DefaultValue = "USA";
sqlSource.SelectParameters.Add(country);
// Add the SqlDataSource to the page controls collection.
Page.Controls.Add(sqlSource);
DataGrid1.DataSource = sqlSource;
DataGrid1.DataBind();
}
}
L'exemple de code suivant montre comment étendre la classe Parameter pour créer un nouveau type de paramètre qui peut être utilisé par les contrôles de source de données et d'autres contrôles dans les scénarios de liaison de données. Un contrôle de source de données peut utiliser un paramètre StaticParameter pour créer une liaison avec la valeur de tout objet, en général une chaîne, déclarée sur une page Web Forms.
Imports System
Imports System.ComponentModel
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Namespace Samples.AspNet
<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
Public Class StaticParameter
Inherits Parameter
Public Sub New()
End Sub
' The StaticParameter(string, object) constructor
' initializes the DataValue property and calls the
' Parameter(string) constructor to initialize the Name property.
Public Sub New(name As String, value As Object)
MyBase.New(name)
DataValue = value
End Sub
' The StaticParameter(string, TypeCode, object) constructor
' initializes the DataValue property and calls the
' Parameter(string, TypeCode) constructor to initialize the Name and
' Type properties.
Public Sub New(name As String, type As TypeCode, value As Object)
MyBase.New(name, type)
DataValue = value
End Sub
' The StaticParameter copy constructor is provided to ensure that
' the state contained in the DataValue property is copied to new
' instances of the class.
Protected Sub New(original As StaticParameter)
MyBase.New(original)
DataValue = original.DataValue
End Sub
' The Clone method is overridden to call the
' StaticParameter copy constructor, so that the data in
' the DataValue property is correctly transferred to the
' new instance of the StaticParameter.
Protected Overrides Function Clone() As Parameter
Return New StaticParameter(Me)
End Function
' The DataValue can be any arbitrary object and is stored in ViewState.
Public Property DataValue() As Object
Get
Return ViewState("Value")
End Get
Set
ViewState("Value") = value
End Set
End Property
' The Value property is a type safe convenience property
' used when the StaticParameter represents string data.
' It gets the string value of the DataValue property, and
' sets the DataValue property directly.
Public Property Value() As String
Get
Dim o As Object = DataValue
If o Is Nothing OrElse Not TypeOf o Is String Then
Return String.Empty
End If
Return CStr(o)
End Get
Set
DataValue = value
OnParameterChanged()
End Set
End Property
' The Evaluate method is overridden to return the
' DataValue property instead of the DefaultValue.
Protected Overrides Function Evaluate(context As HttpContext, control As Control) As Object
If context Is Nothing Then
Return Nothing
Else
Return DataValue
End If
End Function
End Class ' StaticParameter
End Namespace ' Samples.AspNet
namespace Samples.AspNet {
using System;
using System.ComponentModel;
using System.Security.Permissions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
[AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
public class StaticParameter : Parameter {
public StaticParameter() {
}
// The StaticParameter(string, object) constructor
// initializes the DataValue property and calls the
// Parameter(string) constructor to initialize the Name property.
public StaticParameter(string name, object value) : base(name) {
DataValue = value;
}
// The StaticParameter(string, TypeCode, object) constructor
// initializes the DataValue property and calls the
// Parameter(string, TypeCode) constructor to initialize the Name and
// Type properties.
public StaticParameter(string name, TypeCode type, object value) : base(name, type) {
DataValue = value;
}
// The StaticParameter copy constructor is provided to ensure that
// the state contained in the DataValue property is copied to new
// instances of the class.
protected StaticParameter(StaticParameter original) : base(original) {
DataValue = original.DataValue;
}
// The Clone method is overridden to call the
// StaticParameter copy constructor, so that the data in
// the DataValue property is correctly transferred to the
// new instance of the StaticParameter.
protected override Parameter Clone() {
return new StaticParameter(this);
}
// The DataValue can be any arbitrary object and is stored in ViewState.
public object DataValue {
get {
return ViewState["Value"];
}
set {
ViewState["Value"] = value;
}
}
// The Value property is a type safe convenience property
// used when the StaticParameter represents string data.
// It gets the string value of the DataValue property, and
// sets the DataValue property directly.
public string Value {
get {
object o = DataValue;
if (o == null || !(o is string))
return String.Empty;
return (string)o;
}
set {
DataValue = value;
OnParameterChanged();
}
}
// The Evaluate method is overridden to return the
// DataValue property instead of the DefaultValue.
protected override object Evaluate(HttpContext context, Control control) {
if (context.Request == null)
return null;
return DataValue;
}
}
}
Informations de version
.NET FrameworkPris en charge dans : 4, 3.5, 3.0, 2.0
Plateformes
Windows 7, Windows Vista SP1 ou ultérieur, Windows XP SP3, Windows XP SP2 Édition x64, Windows Server 2008 (installation minimale non prise en charge), Windows Server 2008 R2 (installation minimale prise en charge avec SP1 ou version ultérieure), Windows Server 2003 SP2
Le .NET Framework ne prend pas en charge toutes les versions de chaque plateforme. Pour obtenir la liste des versions prises en charge, consultez Configuration requise du .NET Framework.
Sécurité des threads
Tous les membres static ( Shared en Visual Basic) publics de ce type sont thread-safe. Il n'est pas garanti que les membres d'instance soient thread-safe.
Voir aussi
RéférenceAutres ressources
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