ContextItemCollection Class

Article
11/17/2011

The ContextItemCollection class maintains a set of context items. A context item represents a piece of transient state in a designer. ContextItems must define an empty constructor. This empty constructor version of a context item represents its default value, and will be the value returned from GetItem if the context item manager does not contain a context item of the requested type. The ContextItemCollection supports context layers. A context layer is a separation in the set of context items and is useful when providing modal functions. For example, when switching modes in the designer to show the tab order layout it may be desirable to disable adding items from the toolbox and change the user mouse and keyboard gestures to focus on setting the tab order. Rather than grabbing and storing context items before replacing them with new values, a developer can simply call CreateLayer. Once the layer is created, all subsequent context changes go to that layer. When the developer is done with the layer, as would be the case when a user switches out of tab order mode, she simply calls Remove on the layer. This removes all context items that were added to the layer and restores the context to its previous set of values before the layer was created.

Inheritance Hierarchy

System..::..Object
Microsoft.Data.Tools.Design.Core.Context..::..ContextItemCollection

Namespace: Microsoft.Data.Tools.Design.Core.Context
Assembly: Microsoft.Data.Tools.Design.Core (in Microsoft.Data.Tools.Design.Core.dll)

Syntax

'Declaration
Public MustInherit Class ContextItemCollection _
    Implements IEnumerable(Of ContextItem), IEnumerable
'Usage
Dim instance As ContextItemCollection

public abstract class ContextItemCollection : IEnumerable<ContextItem>, 
    IEnumerable

public ref class ContextItemCollection abstract : IEnumerable<ContextItem^>, 
    IEnumerable

[<AbstractClassAttribute>]
type ContextItemCollection =  
    class
        interface IEnumerable<ContextItem>
        interface IEnumerable
    end

public abstract class ContextItemCollection implements IEnumerable<ContextItem>, IEnumerable

The ContextItemCollection type exposes the following members.

Constructors

	Name	Description
	ContextItemCollection	Creates a new ContextItemCollection object.

Top

Methods

	Name	Description
	Contains(Type)	Returns true if the item collection contains an item of the given type.
	Contains< (Of < <' (TItemType> ) > > )() () () ()	Returns true if the item manager contains an item of the given type.
	CreateLayer	Creates a new editing context layer. Editing context layers can be used to create editing modes. For example, you may create a layer before starting a drag operation on the designer. Any new context items you add to the layer hide context items underneath it. When the layer is removed, all context items under the layer are re-surfaced. This allows you to create a layer and set overrides for context items during operations such as drag and drop.
	Equals	(Inherited from Object.)
	Finalize	(Inherited from Object.)
	GetEnumerator	Enumerates the context items in the editing context. This enumeration includes prior layers unless the enumerator hits an isolated layer. Enumeration is typically not useful in most scenarios but it is provided so that developers can search in the context and learn what is placed in it.
	GetHashCode	(Inherited from Object.)
	GetTarget	This is a helper method that returns the target object for a delegate. If the delegate was created to proxy a generic delegate, this will correctly return the original object, not the proxy.
	GetType	(Inherited from Object.)
	GetValue(Type)	Returns an instance of the requested item type. If there is no context item with the given type, an empty item will be created.
	GetValue< (Of < <' (TItemType> ) > > )() () () ()	Returns an instance of the requested item type. If there is no context item with the given type, an empty item will be created.
	MemberwiseClone	(Inherited from Object.)
	NotifyItemChanged	This is a helper method that invokes the protected OnItemChanged method on ContextItem.
	RemoveCallback	This is a helper method that performs a Delegate.Remove, but knows how to unwrap delegates that are proxies to generic callbacks. Use this in your Unsubscribe implementations.
	SetValue	This sets a context item to the given value. It is illegal to pass null here. If you want to set a context item to its empty value create an instance of the item using a default constructor.
	Subscribe(Type, SubscribeContextCallback)	Adds an event callback that will be invoked with a context item of the given item type changes.
	Subscribe< (Of < <' (TContextItemType> ) > > )(SubscribeContextCallback< (Of < <' (TContextItemType> ) > > ))	Adds an event callback that will be invoked with a context item of the given item type changes.
	ToString	(Inherited from Object.)
	Unsubscribe(Type, SubscribeContextCallback)	Removes a subscription.
	Unsubscribe< (Of < <' (TContextItemType> ) > > )(SubscribeContextCallback< (Of < <' (TContextItemType> ) > > ))	Removes a subscription.