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I’ve been using MVVM since I started WPF (I was a latecomer to the beauty that is WPF) and one of the things that’s always irked me is the amount of code you need to write in order to expose a command. I’ll typically write something like the following in order to create a command that I can bind to from the UI…

Silverlight 4 now came up with the support of Command Binding. Using Command binding you can easily develop your Silverlight MVVM (Model-View-ViewModel) applications where your view will not know about data. In this article, I will describe you the Command binding feature in Silverlight 4 Step-by-Step.

By reverse engineering of default InvokeCommandAction I find that blend team just ignores event args.

To resolve this issue I have created my own action for triggering delegate commands.

In Silverlight 4, ButtonBase (and all its derived versions) and HyperlinkButton now support Command and CommandParameter to tie ICommand implementations.  For example, in XAML I can tie two different buttons to the SaveCommand that I have on some object i’ve bound to my UI.

For those of you who have been living in the world of WPF, this post will be old-hat, but for the purely Silverlight folks I am hoping to help you change the way you add functionality to your applications.

Jeff Prosise discusses one of the exciting new features in the Silverlight 4 beta, namely a pair of properties added to the ButtonBase and Hyperlink classes named Command and CommandParameter.

These properties represent the first real support in Silverlight for commanding, which is primarily beneficial to to Model-View-ViewModel (MVVM) applications. MVVM has long been popular among WPF developers and is rapidly gaining popularity with Silverlight developers. And now, thanks to commanding, Silverlight comes a little closer to supporting pure MVVM implementations without help from auxiliary frameworks such as Prism.

 In this screencast Michael Wolf shows how to simply execute any command from Silverlight.

In my last post on out of browser we showed how easy and powerful it is , all be it a bit of a step back in the development time machine, to execute native windows applications using the new com support in silverlight 4. The next logical question arises, that if you can execute com can you also execute a local process. The answer is yes and no. You can execute a local process, not using System.Diagnostics.Process.Start() like you would in the full CLR, but using the COM inerop and the Windows Script Host . The Windows Script Host is a multi purpose COM object that’s shipped with Windows since Win 98, and generally used for automation tasks, which makes it perfect for use in silverlight com inerop. 

In Silverlight, parts of the “plumbing” are available already (the ICommand interface) but most of it is missing. This led some very clever people to implement Commands in Silverlight, to replace the missing pieces by a custom implementation. In Prism, the command implementation is called DelegateCommand. In my MVVM Light Toolkit, I use a command that my good friend, colleague at IdentityMine and fellow WPF Disciple Josh Smith created, called the RelayCommand.

In this second MVVM post Nigel Sampson produces an ExecuteCommand that provides support for Commands.

In the first post of the series we looked at using Binding expressions to display data from the ViewModel on our screen. The other major part of our interaction is having the view invoke functionality in the ViewModel. In the MVVM pattern this is done using the Command pattern, specifically the ICommand interface.

Read Nigel's previous post called "Blendable MVVM : Introduction and Databinding".