CustomExpression Class

.NET Framework (current version)

Provides a way to specify a custom LINQ query that is called in response to an event.

Namespace: System.Web.UI.WebControls.Expressions
Assembly: System.Web.Extensions (in System.Web.Extensions.dll)

Inheritance Hierarchy

System::Object
System.Web.UI.WebControls.Expressions::DataSourceExpression
System.Web.UI.WebControls.Expressions::ParameterDataSourceExpression
System.Web.UI.WebControls.Expressions::CustomExpression

Syntax

C++

public ref class CustomExpression : ParameterDataSourceExpression

Constructors

	Name	Description
	CustomExpression()	Initializes a new instance of the CustomExpression class.

Properties

	Name	Description
	Context	Gets the HttpContext instance of the owner control.(Inherited from DataSourceExpression.)
	DataSource	Gets the data source object that is associated with the owner control.(Inherited from DataSourceExpression.)
	IsTrackingViewState	Gets a value that indicates whether a data source expression object is tracking its view state changes.(Inherited from DataSourceExpression.)
	Owner	Gets the owner control.(Inherited from DataSourceExpression.)
	Parameters	Gets the parameters that are associated with this DataSourceExpression object.(Inherited from ParameterDataSourceExpression.)
	ViewState	Gets an instance of the StateBag class that contains the current view state information.(Inherited from DataSourceExpression.)

Methods

	Name	Description
	Equals(Object^)	Determines whether the specified object is equal to the current object.(Inherited from Object.)
	Finalize()	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)
	GetHashCode()	Serves as the default hash function. (Inherited from Object.)
	GetQueryable(IQueryable^)	Provides access to the modified IQueryable object that the data source uses.(Overrides DataSourceExpression::GetQueryable(IQueryable^).)
	GetType()	Gets the Type of the current instance.(Inherited from Object.)
	LoadViewState(Object^)	Loads the state of the values in the ParameterDataSourceExpression object that must be persisted.(Inherited from ParameterDataSourceExpression.)
	MemberwiseClone()	Creates a shallow copy of the current Object.(Inherited from Object.)
	SaveViewState()	Saves the current view state of the ParameterDataSourceExpression object.(Inherited from ParameterDataSourceExpression.)
	SetContext(Control^, HttpContext^, IQueryableDataSource^)	Executes the expression by using the specified owner control, context, and data source.(Inherited from ParameterDataSourceExpression.)
	SetDirty()	Marks the DataSourceExpression object so that its state will be saved in view state.(Inherited from DataSourceExpression.)
	ToString()	Returns a string that represents the current object.(Inherited from Object.)
	TrackViewState()	Tracks view-state changes of the ParameterDataSourceExpression object so that the changes can be stored in the StateBag object for the object.(Inherited from ParameterDataSourceExpression.)

Events

	Name	Description
	Querying	Occurs when the IQueryable data source value is set.

Explicit Interface Implementations

	Name	Description
	IStateManager::LoadViewState(Object^)	When implemented by a class, loads the previously saved view state of the data source expression object.(Inherited from DataSourceExpression.)
	IStateManager::SaveViewState()	When implemented by a class, saves the current view state of the DataSourceExpression object.(Inherited from DataSourceExpression.)
	IStateManager::TrackViewState()	When implemented by a class, tracks view state changes of the DataSourceExpression object so that the changes can be stored in the StateBag object for the data source expression object.(Inherited from DataSourceExpression.)
	IStateManager::IsTrackingViewState	When implemented by a class, gets a value that indicates whether a data source expression object is tracking its view state changes.(Inherited from DataSourceExpression.)

The CustomExpression class is used with the QueryExtender control. The QueryExtender control supports a variety of options that you can use to filter data. The QueryExtender control supports filters that let you search strings, search values between a specified range, compare a property value in a table to a specified value, and sort data. These options are provided as LINQ expressions in the QueryExtender control. You can use these filter expressions or you can provide a custom expression that you can use in the QueryExtender control. The CustomExpression class enables you to specify a custom expression in your application and call it in an event handler.

Note
You can provide a custom query that is called by a method instead of an event handler by using the MethodExpression class.

Examples

The following example shows how to create a CustomExpression object that is used by the QueryExtender control. The custom expression calls the FilterProducts method, which contains a custom LINQ expression. The result of the filtering operation is displayed in a GridView control.

The following example shows an event handler that contains a custom LINQ query. The expression filters the Product table in the AdventureWorks database and displays products that have a list price greater than or equal to $3,500.00.

C++

No code example is currently available or this language may not be supported.

Version Information

.NET Framework
Available since 4.0

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.