The OneTime parameter in this example causes the framework to disable the button. Removing the OneTime parameter or changing it to OneWay fixes the problem.

I was not implementing INotifyPropertyChanged in my calculator class. Easy fix.

Hello Rob! At one time the RoutedUIMessaging namespace obviously existed. It does not exist now but your sample code in the documentation usually references it. Also, i'm not able to get this sample to work using Silverlight 3. I have the latest Caliburn source. The button does not enable. If ialways return true from the CanDivide method the button enables but the Divide method does not get called. I am going t o keep working on it but if you have any thoughts that would be great.

Rob, Can you supply me an example how to pass the object to the global command that invokes this command. Example: I have a listbox and each listboxitem is a Person object. I have a global command EditPerson(Person person). In DataTemplate I have: ... <Button ... cal:Command.Parent="{StaticResource Any}"... ... How can I to pass the ListBoxItem (Person object) into the global command? Because you supplied examples how to pass values from another controls from the visual tree. Thanks,

@JavedSaqib: Would be nice, but unfortunately CLR doesn't permit, as far I know, to have lambda or Expression as attribute property.

Hi would be nice if all Attributes would accept lamda expressions or or type safe variants instead of strings like [AsyncAction(Callback = "DivideComplete", BlockInteraction = true)] and [Preview("CanDivide")] could be changed to [AsyncAction(Callback = instance => instance.DivideComplete , BlockInteraction = true)] and [Preview(x=>x.CanDivide)] with taking lambdas the attributes could bind type safe the methods. (So the lamda should in this case return as result a delegate to method)

Fixed. Thanks for finding that error.

OK. Fixed the errors. Thanks for catching those.

Thanks for finding those errors. I've got them fixed now.

palesz, you can see the BackgroundProcessing sample under HowTo for an example of this.