How should I implement multiple views on the same data?

I have a MVVM/WPF based application that can have multiple workspaces (basically containing a TreeView) open at the same time that display and operate on the same data tree. I need to be able to expand and collapse and select the items in each workspace independently and I want to be able to drag and drop items between the two workspaces (e.g. for moving or duplicating items). I also need data virtualization in that the data is only loaded (in both views) when a tree item is expanded for the first time. There is also one workspace-wide details view that shows the details of the selected item of the workspace that currently has the focus. Workspace specific expansion and selection of items must also work programatically.

Cou开发者_开发百科ld you layout a ruff design for a MVVM based application that embraces theses features? Should I create a separate ViewModel tree for each workspace and implement a Model-ViewModel mapper? Or should I have just one ViewModel tree with two Views? How does the details view know what is currently selected and what workspace has the focus? ...

So to rephrase my question: The Model instances displayed in each View are actually the same instances. But should the ViewModels be the same too? Or better: Could I possibly get away with that?

Also: Is there an open source application I could study that has most of these features? Could Prism or any other MVVM based framework do most of that work for me?

There is a direct correlation between View and ViewModel. The View shows a visual representation of the Model, hosted and "formatted" by the ViewModel.

Since you will have different Model (data) on each View, you need to have several instances of your ViewModel hosting each set of different data.

Now the question is: do your ViewModels share some entities or objects between them ? If yes, could they change during your application lifetime, and do you want to see these changes in realtime in your TreeViews ?

You then have two options:

1. Directly bind the model to the View (if the model implements INotifyPropertyChanged) by exposing it through your ViewModel: then all your views will be automatically updated when a model property changes.
2. Create a component which supervises Model modifications and notify ViewModel exposing them.

The second solution is more pure than the first one because Models should be POCO and shouldn't implement some plumbing oriented-interface. ViewModel should handle the plumbing.

However it's more complicated to design, and 90% of the time, you will end-up saying "come on, just one little interface doesn't hurt" :)

For your details view. You can communicate between your TreeViewModel and your DetailViewModel using a mediator (Messenger in the MVVM Light Toolkit), which is basically a low-coupled event-oriented component. Or use a supervisor which is injected in all your ViewModel and notify them using events.

Speaking of MVVM framework, and for common architecture like the one you are describing, I would recommend the MVVM Light Toolkit.

Maybe I am missing something, but is it not possible to have 2 instances of the same View / ViewModel loaded with different data?