MVVM Routed and Relay Command

Question

What is the Difference between the RoutedCommand and RelayCommand ? When to use RoutedCommand and when to use RelayCommand in MVVM pattern ?

Answer 1

The difference is that RelayCommand can accept delegates. You can define the RelayCommand outside of the ViewModel. The ViewModel can then add delegates to the command when it creates and binds the command to an UI object like a control. The delegates in turn can access the private variable of the ViewModel as they are defined in the scope of the View Model itself.

It is used to cut down on the amount of code contained in the ViewModel as the trend is to define a Routed command as a nested class inside the ViewModel. The functionality of the two is otherwise similar.

Answer 2

RoutedCommand is part of WPF, while RelayCommand was created by a WPF Disciple, Josh Smith ;).

Seriously, though, RS Conley described some of the differences. The key difference is that RoutedCommand is an ICommand implementation that uses a RoutedEvent to route through the tree until a CommandBinding for the command is found, while RelayCommand does no routing and instead directly executes some delegate. In a M-V-VM scenario a RelayCommand (DelegateCommand in Prism) is probably the better choice all around.