Where should I define my datatemplates?

Question

I'm trying to work out the best way to couple my Views and ViewModels in MVVM and I've settled on the ViewModel-first approach using typed DataTemplates, as described in this article and in this answer. I'm using Prism and have multiple modules which have their own projects/class libraries.

My question is: Where should my DataTemplates live in my solution?

1. Should I put the DataTemplates in a Resource Dictionary which lives in the same project that has the types/ViewModels it renders?
2. Should I put the DataTemplates in a Resource Dictionary which lives in the project which has the application's MainWindow (i.e. Shell.xaml)?
3. Should these Resource Dictionaries then be added to App.Current.MainWindow.Resources.MergedDictionaries?

I hope this is enough information to describe what I'm trying to do.

Update: see comments of selected answer.

Answer 1

I'm sure that the best way here is to use Themes\Generic.xaml resources file. This is file (it should be exactly in folder Themes and has name exactly Generic.xaml) used by WPF/Silverlight themes engine and contains resources shared through whole application. You can also create separate file in folder Themes with name like Generic.DataTemplates.xaml and add link to it from Generic.xaml. Google knows a lot about generic.xaml or you can see more details in my answer here: WPF Prism - Where to put Resources?