ContextItem Class

Represents a single piece of state in the designer.

Inheritance Hierarchy


Namespace:  Microsoft.Windows.Design
Assembly:  Microsoft.Windows.Design.Extensibility (in Microsoft.Windows.Design.Extensibility.dll)


Public MustInherit Class ContextItem
public abstract class ContextItem
public ref class ContextItem abstract
type ContextItem =  class end
public abstract class ContextItem

The ContextItem type exposes the following members.


  Name Description
Protected method ContextItem Initializes a new instance of the ContextItem class.



  Name Description
Public property ItemType When overridden in a derived class, gets the item type for this editing context item.



  Name Description
Public method Equals Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected method Finalize Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public method GetHashCode Serves as a hash function for a particular type. (Inherited from Object.)
Public method GetType Gets the Type of the current instance. (Inherited from Object.)
Protected method MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
Protected method OnItemChanged Called on a context item before it is stored in the context item manager.
Public method ToString Returns a string that represents the current object. (Inherited from Object.)



Context items are immutable objects that contain state. Some context items also define methods that can perform operations on the state they contain. ContextItem is the base class from which all context items must derive.

A context item may come and go in an editing context. Context items are transient, but they always have a value. Even if a particular context item is not in the context, a default value is always provided. Therefore, the context never returns nulla null reference (Nothing in Visual Basic).

Unlike a service, the value of a context item can change at any moment. This means that you should not cache context items. Code that uses the context can subscribe to a SubscribeContextCallback<TContextItemType> that is raised when a particular type of context item changes.

A class derived from ContextItem must define an empty constructor. This empty constructor version of a context item represents its default value. This default value is the value returned from GetValue if the ContextItemManager does not contain a context item of the requested type.

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


Microsoft.Windows.Design Namespace





Other Resources

Editing Context Architecture

Understanding WPF Designer Extensibility