WeakEventManager Class (System.Windows)

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.NET Framework Class Library

WeakEventManager Class

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Provides a base class for the event manager that is used in the weak event pattern. The manager adds and removes listeners for events (or callbacks) that also use the pattern.

Inheritance Hierarchy

System.Object
  System.Windows.Threading.DispatcherObject
    System.Windows.WeakEventManager
      More...

Namespace: System.Windows
Assembly: WindowsBase (in WindowsBase.dll)

Syntax

Visual Basic


Public MustInherit Class WeakEventManager _
	Inherits DispatcherObject


public abstract class WeakEventManager : DispatcherObject

Visual C++


public ref class WeakEventManager abstract : public DispatcherObject


[<AbstractClass>]
type WeakEventManager =  
    class
        inherit DispatcherObject
    end

The WeakEventManager type exposes the following members.

Constructors

	Name	Description
	WeakEventManager	Initializes base class values when it is used as the initializer by the constructor of a derived class.

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Properties

	Name	Description
	Dispatcher	Gets the Dispatcher this DispatcherObject is associated with. (Inherited from DispatcherObject.)
	Item	Gets or sets the data being stored for the specified source.
	ReadLock	Establishes a read-lock on the underlying data table, and returns an IDisposable.
	WriteLock	Establishes a write-lock on the underlying data table, and returns anIDisposable.

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Methods

	Name	Description
	CheckAccess	Determines whether the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
	DeliverEvent	Delivers the event being managed to each listener.
	DeliverEventToList	Delivers the event being managed to each listener in the provided list.
	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.)
	GetCurrentManager	Returns the WeakEventManager implementation that is used for the provided type.
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	NewListenerList	Returns a new object to contain listeners to an event.
	ProtectedAddHandler	Adds the specified delegate as an event handler of the specified source.
	ProtectedAddListener	Adds the provided listener to the provided source for the event being managed.
	ProtectedRemoveHandler	Removes the previously added handler from the specified source.
	ProtectedRemoveListener	Removes a previously added listener from the provided source.
	Purge	Removes inactive listener entries from the data list for the provided source. Returns true if some entries were actually removed from the list.
	Remove	Removes all listeners for the specified source.
	ScheduleCleanup	Requests that a purge of unused entries in the underlying listener list be performed on a lower priority thread.
	SetCurrentManager	Sets the current manager for the specified manager type.
	StartListening	When overridden in a derived class, starts listening for the event being managed. After the StartListening method is first called, the manager should be in the state of calling DeliverEvent or DeliverEventToList whenever the relevant event from the provided source is handled.
	StopListening	When overridden in a derived class, stops listening on the provided source for the event being managed.
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	VerifyAccess	Enforces that the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)

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Remarks

You typically use the weak event pattern when the event source has an object lifetime that is independent of the event listeners. Using the central event dispatching capability of a WeakEventManager allows the listener's handlers to be garbage collected even if the source object persists. By contrast, a regular event hookup using the += operator causes the potentially disconnected source to hold a reference to the listeners. This prevents the receiver from being garbage collected in a timely fashion.

One common situation where the lifetime relationships between sources and listeners should use of the weak event pattern is the handling of update events coming from data bindings.

The weak event pattern can also be used for callbacks and regular events.

Notes to Inheritors

For an example of a custom WeakEventManager, see Weak Event Patterns.

Version Information

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Platforms

Windows 8 Release Preview, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 SP2, Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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.

Reference

System.Windows Namespace

IWeakEventListener

Other Resources

Weak Event Patterns

Data Binding Overview

Inheritance Hierarchy