Parameter Parameter Parameter Parameter Class
Definition
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.
public ref class Parameter : ICloneable, System::Web::UI::IStateManager
public class Parameter : ICloneable, System.Web.UI.IStateManager
type Parameter = class
interface ICloneable
interface IStateManager
Public Class Parameter
Implements ICloneable, IStateManager
- Inheritance
- Derived
-
System.Web.DynamicData.DynamicControlParameterSystem.Web.DynamicData.DynamicControlParameterSystem.Web.DynamicData.DynamicControlParameterSystem.Web.DynamicData.DynamicControlParameterSystem.Web.DynamicData.DynamicQueryStringParameterSystem.Web.DynamicData.DynamicQueryStringParameterSystem.Web.DynamicData.DynamicQueryStringParameterSystem.Web.DynamicData.DynamicQueryStringParameterSystem.Web.UI.WebControls.ControlParameterSystem.Web.UI.WebControls.ControlParameterSystem.Web.UI.WebControls.ControlParameterSystem.Web.UI.WebControls.ControlParameterSystem.Web.UI.WebControls.CookieParameterSystem.Web.UI.WebControls.CookieParameterSystem.Web.UI.WebControls.CookieParameterSystem.Web.UI.WebControls.CookieParameterSystem.Web.UI.WebControls.FormParameterSystem.Web.UI.WebControls.FormParameterSystem.Web.UI.WebControls.FormParameterSystem.Web.UI.WebControls.FormParameterSystem.Web.UI.WebControls.ProfileParameterSystem.Web.UI.WebControls.ProfileParameterSystem.Web.UI.WebControls.ProfileParameterSystem.Web.UI.WebControls.ProfileParameterSystem.Web.UI.WebControls.QueryStringParameterSystem.Web.UI.WebControls.QueryStringParameterSystem.Web.UI.WebControls.QueryStringParameterSystem.Web.UI.WebControls.QueryStringParameterSystem.Web.UI.WebControls.RouteParameterSystem.Web.UI.WebControls.RouteParameterSystem.Web.UI.WebControls.RouteParameterSystem.Web.UI.WebControls.RouteParameter
- Implements
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 xmlns="http://www.w3.org/1999/xhtml" >
<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 xmlns="http://www.w3.org/1999/xhtml" >
<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="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 xmlns="http://www.w3.org/1999/xhtml" >
<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="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 xmlns="http://www.w3.org/1999/xhtml" >
<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.
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();
}
}
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
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.
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;
}
}
}
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
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.
ControlParameter | Binds any public property of a Web server control. |
FormParameter | Binds a form field. |
SessionParameter | Binds a session-state field. |
RouteParameter | Binds a route URL parameter. |
CookieParameter | Binds a cookie field. |
QueryStringParameter | Binds a query-string parameter. |
ProfileParameter | Binds a profile field. |
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 null
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.
Constructors
Properties
ConvertEmptyStringToNull ConvertEmptyStringToNull ConvertEmptyStringToNull ConvertEmptyStringToNull |
Gets or sets a value indicating whether the value that the Parameter object is bound to should be converted to |
DbType DbType DbType DbType |
Gets or sets the database type of the parameter. |
DefaultValue DefaultValue DefaultValue DefaultValue |
Specifies a default value for the parameter, should the value that the parameter is bound to be uninitialized when the Evaluate(HttpContext, Control) method is called. |
Direction Direction Direction Direction |
Indicates whether the Parameter object is used to bind a value to a control, or the control can be used to change the value. |
IsTrackingViewState IsTrackingViewState IsTrackingViewState IsTrackingViewState |
Gets a value indicating whether the Parameter object is saving changes to its view state. |
Name Name Name Name |
Gets or sets the name of the parameter. |
Size Size Size Size |
Gets or sets the size of the parameter. |
Type Type Type Type |
Gets or sets the type of the parameter. |
ViewState ViewState ViewState ViewState |
Gets a dictionary of state information that allows you to save and restore the view state of a Parameter object across multiple requests for the same page. |