WeakEventManager.ListenerList Class

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

Namespace: System.Windows
Assembly: WindowsBase (in windowsbase.dll)
XML Namespace:  http://schemas.microsoft.com/winfx/2006/xaml/presentation

protected class ListenerList
protected class ListenerList
protected class ListenerList
<ListenerList .../>

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.


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

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0

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