THE feature that was missing from WPF ! Visual Studio 2010 beta 2 has been released last week, and it brings to WPF a long awaited feature : support for bindings in InputBindings.
As a reminder, the issue in previous releases was that the Command property of the InputBinding class wasn’t a DependencyProperty, so it wasn’t possible to bind it. Furthermore, InputBindings didn’t inherit the parent DataContext, which made it difficult to provide alternative implementations…
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 :
It’s quite simple, in WPF, to present data in a grid, thanks to the GridView class. If you want to sort it, however, it gets a little harder… With the DataGridView in Windows Forms, it was “automagic” : when the user clicked a column header, the grid was automatically sorted. To achieve the same behavior in WPF, you need to get your hands dirty… The method recommended by Microsoft is described in this article ; it is based on the Click event of the GridViewColumnHeader class.
If you develop WPF applications according to the Model-View-ViewModel pattern, you may have faced this issue : in XAML, how to bind a key or mouse gesture to a ViewModel command ? The obvious and intuitive approach would be this one :
<UserControl.InputBindings> <KeyBinding Modifiers="Control" Key="E" Command="{Binding EditCommand}"/> </UserControl.InputBindings> Unfortunately, this code doesn’t work, for two reasons :
The Command property is not a dependency property, so you cannot assign it through binding InputBindings are not part of the logical or visual tree of the control, so they don’t inherit the DataContext A solution would be to create the InputBindings in the code-behind, but in the MVVM pattern we usually prefer to avoid this… I spent a long time looking for alternative solutions to do this in XAML, but most of them are quite complex and unintuitive.
Soon after the release of WPF, people have been talking more and more about “Model-View-ViewModel” (MVVM). This expression refers to a design pattern, drawing its inspiration from the Model-View-Controller (MVC) and Presentation Model (PM) patterns, and created specifically to take advantage of WPF features. This patterns enables an excellent decoupling between data, behavior and presentation, which makes the code easier to understand and maintain, and improves the collaboration between developers and designers.