mvvm - WPF M-V-VM: Get selected items from a ListCollectionView?

Question

I've got a WPF app using the Model-View-ViewModel pattern.
In my ViewModel I've got a ListCollectionView to keep a list of items.
This ListCollectionView is bound to a ListBox in my View.

<ListBox Grid.Row="1" ItemsSource="{Binding Useragents}" SelectionMode="Multiple"/>

The ListBox has SelectionMode=Multiple, so you can select more items at one time. Now the ViewModel needs to know which items has been selected.

The problem is: in the View-Model-ViewModel pattern the ViewModel has no access to the View, so I can't just ask the ListBox which items has been selected. All I have is the ListCollectionView, but I can't find a way to find which items has been selected in there.

So how do I find which items has been selected in the ListBox? Or a trick to achieve this (maybe bind something to a Boolean 'IsSelected' in my items? But what? How?)

Maybe someone who is using this pattern, too, can help me here?

Answer 1

You need to create a ViewModel that has the concept of IsSelected on it and is bound to the IsSelected property of the actual ListBoxItem that represents it in the View using the standard WPF bindings architecture.

Then in your code, which knows about your ViewModel, but not the fact that it's represented by any specific View, can just use that property to find out which items from the Model are actually selected irrespective of the designers choice for how its represented in the View.