Concrete examples of state sharing between multiple viewmodels (WPF MVVM)
- by JohnMetta
I have a WPF/Entity Framework (4.0) project with many objects. I'd like to build the application so that that I can have object selection state shared across viewmodels.
For Example: We have Cars, Drivers, Passengers, and Cargo classes. We also have UserControls for CarList, DriverList, etc. and editor windows for CarEditor, DriverEditor, etc. Furthermore, we have viewmodels for all of these (CarListViewModel, DriverListViewModel, CargoEditorViewModel, etc). This all composes a dockable interface where the user can have multiple object lists, editors, and viewers open.
What I want is a concrete code example of how to wireup multiple viewmodels so that selecting a car in the CarList will cause that car to go live in the CarEditorView, but also be selected in any other view for which the context is valid (such as a DriverByCarView- or just DriverList if there is a filter predicate).
There are a number of suggestions and discussions based on this question. The two methods that seem to dominate are:
3018307: Discusses state sharing by mentioning a messaging subsystem
1159035: Discusses state sharing by using an enclosing viewmodel
Is one of these approaches better than the other?
Does anyone have a concrete example of either/both of these methods in the form of a write-up or small code project?
I'm still learning WPF, so pointers to entry points for reading API fundamentals are appreciated, but looking at code examples is where I usually go.
Thanks
In case anyone is interested, here are some other similar discussions:
3816961: Discusses returning multiple viewmodels depending on object type (i.e. a collection of arbitrary types adhering to a specific interface)
1928130: Discusses whether it is a good idea to aggregate viewmodels as properties of other viewmodels (e.g. a MainWindow viewmodel composed of panel viewmodels)
1120061: Essentially discusses whether to have use a viewmodel-per-model strategy or a viewmodel-per-view-element strategy.
4244222: Discusses whether or not to nest the viewmodels when using a nested object hierarchy.
4429708: Discusses sharing collections between viewmodels directly, but doesn't go into detail.
List item: Discusses managing multiple selections within a single viewmodel.
