This documentation is archived and is not being maintained.

WeakEventManager.ListenerList Class

Provides a built-in collection list for storing listeners for a WeakEventManager.


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

protected class ListenerList
You cannot use this class in XAML.

The WeakEventManager.ListenerList type exposes the following members.

Public methodWeakEventManager.ListenerList()Initializes a new instance of the WeakEventManager.ListenerList class.
Public methodWeakEventManager.ListenerList(Int32)Initializes a new instance of the WeakEventManager.ListenerList class with the specified initial capacity.

Public propertyCountGets the number of items contained in the WeakEventManager.ListenerList.
Public propertyStatic memberEmptyGets a value that represents an empty list for purposes of comparisons.
Public propertyIsEmptyGets a value that declares whether this WeakEventManager.ListenerList is empty.
Public propertyItemGets or sets a specific listener item in the WeakEventManager.ListenerList .

Public methodAddAdds a listener item to the WeakEventManager.ListenerList.
Public methodBeginUseDeclares the list to be in use. This prevents direct changes to the list during iterations of the list items.
Public methodCloneCreates a modifiable clone of this WeakEventManager.ListenerList, making deep copies of the values.
Public methodEndUseUnlocks the locked state initiated by BeginUse.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodStatic memberPrepareForWritingChecks to see whether the provided list is in use, and if so, sets the list reference parameter to a copy of that list rather than the original.
Public methodPurgeRemoves all entries from the list where the underlying reference target is a null reference.
Public methodRemoveRemoves the first occurrence of a listener item from the WeakEventManager.ListenerList.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)

Although this list contains members that resemble those defined by IList and ICollection, and provide similar functionality, this class implements neither of those interfaces.

Most WeakEventManager derived classes do not need to use any members on WeakEventManager.ListenerList. The WeakEventManager methods ProtectedAddListener and ProtectedRemoveListener use a default WeakEventManager.ListenerList internally, one list for each source.

You only need to call WeakEventManager.ListenerList methods if your WeakEventManager class maintains multiple lists for the same event-source combination, with each list created to account for different conditions of the event. In this case, you would not use ProtectedAddListener and ProtectedRemoveListener and would instead implement AddListener or RemoveListener to act upon listeners in just one of the internal listener lists, typically based on a parameter that you add to AddListener or RemoveListener. Also, the handler implementation that receives the raw event cannot simply call DeliverEvent; you must instead keep track of the specifics of the event and deliver the event only to the appropriate list using DeliverEventToList.

The various methods of WeakEventManager.ListenerList are provided so that you can work with your internal lists and so that you can prevent modification of the list during actual delivery of the event.

An example class that used this implementation technique is PropertyChangedEventManager, which maintains separate listener lists for PropertyChanged based on which property changed.

.NET Framework

Supported in: 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.