A few years ago, I blogged about a generic implementation of the weak event pattern in C#. The goal was to mitigate the memory leaks associated with events when you forget to unsubscribe. The implementation was based on the use of weak references to the subscribers, to allow them to be garbage collected. My initial solution was more a proof of concept than anything else, and had a major performance issue, due to the use of DynamicInvoke every time the event was raised.
It's been a while since I last wrote about markup extensions… The release of Visual Studio 11 Developer Preview, which introduces a number of new features to WPF, just gave me a reason to play with them again. The feature I'm going to discuss here is perhaps not the most impressive, but it fills in a gap of the previous versions: the support of markup extensions for events. Until now, it was possible to use a markup extension in XAML to assign a value to a property, but we couldn't do the same to subscribe to an event.