Significance of declaring a WPF event handler as 'async' in C# 5

Question

Imagine a WPF code-behind event handler:

In C# 4 you would declare your handler as:

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Answer 1

A partial answer. From MSDN:

An async method that has a void return type can’t be awaited, and the caller of a void-returning method can't catch any exceptions that the method throws.

So any errors would only be available via the TaskScheduler.

Also, there's nothing XAML-specific going on with the event handler registration. It could have been done in code:

this.button.Click += OnButtonClick;

Or even as an async lambda:

this.button.Click += async (s,e) => { ... };

As for safety of UI updates after an await, it seems that the continuation is executed within SynchronisationContext.Current, which is set per thread. In WPF, this is a DispatcherSynchronisationContext that's coupled to the WPF Dispatcher that pumped the event in the first place.