Asynchronous

Asynchrony in C# 5 is awesome, and I’ve been using it a lot since it was introduced. But there are few annoying limitations; for instance, you cannot pass parameters by reference (ref or out) to an asynchronous method. There are good reasons for that; the most obvious is that if you pass a local variable by reference, it is stored on the stack, but the current stack won’t remain available during the whole execution of the async method (only until the first await), so the location of the variable won’t exist anymore.

As you may have noticed, it is not possible to modify the contents of an ObservableCollection on a separate thread if a view is bound to this collection : the CollectionView raises a NotSupportedException : This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread To illustrate this, let’s take a simple example : a ListBox bound to a collection of strings in the ViewModel :