MVVM Light Toolkit - RelayCommands, DelegateCommands, and ObservableObjects
- by DanM
I just started experimenting with Laurent Bugnion's MVVM Light Toolkit. I think I'm going to really like it, but I have a couple questions.
Before I get to them, I need to explain where I'm coming from. I currently use a combination of Josh Smith's MVVM Foundation and another project on Codeplex called MVVM Toolkit. I use ObservableObject and Messenger from MVVM Foundation and DelegateCommand and CommandReference from MVVM Toolkit.
The only real overlap between MVVM Foundation and MVVM Tookit is that they both have an implementation for ICommand: MVVM Foundation has a RelayCommand and MVVM Tookit has a DelegateCommand. Of these two, DelegateCommand appears to be more sophisticated. It employs a CommandManagerHelper that uses weak references to avoid memory leaks.
With that said, a couple questions:
Why does MVVM Light Toolkit use RelayCommand rather than DelegateCommand? Is the use of weak references in an ICommand unnecessary or not recommended for some reason?
Why is there no ObservableObject in MVVM Light? ObservableObject is basically just the part of ViewModelBase that implements INotifyPropertyChanged, but it's very convenient to have as a separate class because view-models are not the only objects that need to implement INotifyPropertyChanged. For example, let's say you have DataGrid that binds to a list of Person objects. If any of the properties in Person can change while the user is viewing the DataGrid, Person would need to implement INotifyPropertyChanged. (I realize that if Person is auto-generated using something like LinqToSql, it will probably already implement INotifyPropertyChanged, but there are cases where I need to make a view-specific version of entity model objects, say, because I need to include a command to support a button column in a DataGrid.)
Thanks.
