Assembly: WindowsBase (in windowsbase.dll)
XML Namespace: http://schemas.microsoft.com/winfx/2006/xaml/presentation
The principal reason for following the WeakEvent pattern is when the event source has an object lifetime that is potentially independent of the event listeners. Using the central event dispatching of a WeakEventManager allows the listener's handlers to be garbage collected even if the source object persists. By contrast, a normal event hookup using += causes the potentially disconnected source to hold a reference to the listeners, thus keeping the receiver from being collected in a timely fashion.
One common situation where the lifetime relationships between sources and listeners suggests the use of this pattern is the handling of update events coming from sources for data bindings.
The pattern can also be used for callbacks as well as for true events.Notes to Inheritors: Classes that derive from WeakEventManager class should do the following:
Provide a static "AddListener" method. Sources call AddListener to add a listener for the managed weak event. Your implementation calls ProtectedAddListener to implement this behavior.
Provide a static "RemoveListener" method. Sources call RemoveListener to add a listener for the managed event. Your implementation calls ProtectedRemoveListener to implement this behavior.
Override StartListening to cast the source to the type that owns the event, and connect the handler on the source to the event being managed.
Override StopListening to cast the source to the type that owns the event, and disconnect the handler on the source to the event being managed.
Implement the handler, which should call DeliverEvent, so that the managed event is forwarded to its weak event pattern listeners.
Provide a CurrentManager property that returns the specific manager type being implemented. The get accessor for CurrentManager should call GetCurrentManager to make sure that there is not already an initialized instance. If so, that instance is returned, properly typed. If there is no initialized instance, the get accessor should call SetCurrentManager to initialize one.
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 EditionThe Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.