ItemPolicy Class

Artikel
02/23/2011

A policy that specifies a set of rules in the designer.

Inheritance Hierarchy

System.Object
Microsoft.Windows.Design.Policies.ItemPolicy
Microsoft.Windows.Design.Policies.SelectionPolicy

Namespace: Microsoft.Windows.Design.Policies
Assembly: Microsoft.Windows.Design.Interaction (in Microsoft.Windows.Design.Interaction.dll)

Syntax

'Declaration
Public MustInherit Class ItemPolicy

public abstract class ItemPolicy

public ref class ItemPolicy abstract

[<AbstractClass>]
type ItemPolicy =  class end

public abstract class ItemPolicy

The ItemPolicy type exposes the following members.

Constructors

	Name	Description
	ItemPolicy	Initializes a new instance of the ItemPolicy class.

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Properties

	Name	Description
	Context	Gets the editing context for the designer.
	IsSurrogate	Gets a value indicating whether the policy is a surrogate policy.
	PolicyItems	Gets an enumeration of all items in the policy.

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Methods

	Name	Description
	Equals	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 a hash function for a particular type. (Inherited from Object.)
	GetSurrogateItems	Returns an optional set of surrogate items for this item.
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	OnActivated	Called when a policy is activated.
	OnDeactivated	Called when the policy is deactivated.
	OnPolicyItemsChanged	Raises the PolicyItemsChanged event.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Events

	Name	Description
	PolicyItemsChanged	Occurs when the policy changes.

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Remarks

Derive from the abstract ItemPolicy class to provide an association between a set of items and corresponding feature providers.

Use policies to discover extensibility features on items that are running in the designer. Policies are used by tools, adorners, and other areas of the designer that are extensible. The SelectionPolicy class is an example of policy that monitors selection changes and raises the PolicyItemsChanged event when selection changes. The designer handles change events for all running policies and takes appropriate action. In the case of SelectionPolicy, the designer queries for the set of active tasks that should be available and the set of adorners that should be visible on the design surface.

A single instance of a policy type is activated when the designer discovers it in metadata. Policies last for the life of the designer, and are never deactivated unless the designer itself is disposed. If you have a policy that holds a reference to process-global resources, implement the OnDeactivated method, which is called when the policy manager terminates.

A surrogate policy offers an alternative set of items that are used to locate feature providers. Surrogate policies are most often used by control containers that offer additional tasks and adorners on their children. In this scenario, the container offers a surrogate policy in which the GetSurrogateItems method returns the parent of the item provided.

Examples

The following code example shows how to implement a custom surrogate policy for the primary selection. For a full code listing, see How to: Create a Surrogate Policy.

' The DockPanelPolicy class implements a surrogate policy that
' provides container semantics for a selected item. By using 
' this policy, the DemoDockPanel container control offers 
' additional tasks and adorners on its children. 
Class DockPanelPolicy
    Inherits PrimarySelectionPolicy

    Public Overrides ReadOnly Property IsSurrogate() As Boolean 
        Get
            Return True
        End Get
    End Property

    Public Overrides Function GetSurrogateItems( _
        ByVal item As Microsoft.Windows.Design.Model.ModelItem) _
        As System.Collections.Generic.IEnumerable( _
        Of Microsoft.Windows.Design.Model.ModelItem)

        Dim parent As ModelItem = item.Parent

        Dim e As New System.Collections.Generic.List(Of ModelItem)

        If (parent IsNot Nothing) Then

            e.Add(parent)

        End If

        Return e

    End Function

End Class

// The DockPanelPolicy class implements a surrogate policy that
// provides container semantics for a selected item. By using 
// this policy, the DemoDockPanel container control offers 
// additional tasks and adorners on its children. 
class DockPanelPolicy : PrimarySelectionPolicy 
{
    public override bool IsSurrogate 
    {
        get 
        { 
            return true;
        }
    }

    public override IEnumerable<ModelItem> GetSurrogateItems(ModelItem item) 
    {
        ModelItem parent = item.Parent;

        if (parent != null)
        {
            yield return parent;
        }
    }
}

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.

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