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POMVVM Light Toolkit - RelayCommands, DelegateCommands, and ObservableObjects
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copied!<p>I just started experimenting with Laurent Bugnion's <a href="http://mvvmlight.codeplex.com/" rel="nofollow">MVVM Light Toolkit</a>. I think I'm going to really like it, but I have a couple questions.</p> <p>Before I get to them, let me explain where I'm coming from. I currently use a combination of Josh Smith's <a href="http://mvvmfoundation.codeplex.com/" rel="nofollow">MVVM Foundation</a> and another project on Codeplex called <a href="http://wpf.codeplex.com/releases/view/14962" rel="nofollow">MVVM Toolkit</a>. I use <code>ObservableObject</code> and <code>Messenger</code> from MVVM Foundation and <code>DelegateCommand</code> and <code>CommandReference</code> from MVVM Toolkit.</p> <p>The only real overlap between MVVM Foundation and MVVM Tookit is that they both have an implementation for <code>ICommand</code>: MVVM Foundation has <code>RelayCommand</code> and MVVM Tookit has <code>DelegateCommand</code>. Of these two, <code>DelegateCommand</code> appears to be more sophisticated. It employs a <code>CommandManagerHelper</code> that uses weak references to avoid memory leaks.</p> <p>With that said, here are my questions:</p> <ol> <li><p>Why does MVVM Light use <code>RelayCommand</code> rather than <code>DelegateCommand</code>? Is the use of weak references in an <code>ICommand</code> unnecessary or not recommended for some reason?</p></li> <li><p>Why is there no <code>ObservableObject</code> in MVVM Light? <code>ObservableObject</code> is basically just the part of <code>ViewModelBase</code> that implements <code>INotifyPropertyChanged</code>, but it's very convenient to have as a separate class because view-models are not the only objects that need to implement <code>INotifyPropertyChanged</code>. For example, let's say you have a DataGrid that binds to a list of <code>Person</code> objects. If any of the properties in <code>Person</code> can change while the user is viewing the DataGrid, <code>Person</code> would need to implement <code>INotifyPropertyChanged</code>. (I realize that if <code>Person</code> is auto-generated using something like LinqToSql, it will probably already implement <code>INotifyPropertyChanged</code>, but there are cases where I need to make view-specific versions of entity model objects, say, because I need to include a command to support a button column in a DataGrid.)</p></li> </ol> <p>Thanks.</p> <p>P.S. Here is the code for <code>DelegateCommand</code> from the MVVM Toolkit:</p> <p><a href="https://docs.google.com/document/pub?id=1ApCx5SbCfHi5fBhv8Ki3zA6j34sp2t80LQZdj89v8cU" rel="nofollow">https://docs.google.com/document/pub?id=1ApCx5SbCfHi5fBhv8Ki3zA6j34sp2t80LQZdj89v8cU</a></p>

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