How to support ListBox SelectedItems binding with MVVM in a navigable application

c# wpf mvvm listbox
caseklim picture caseklim · Jun 21, 2012 · Viewed 42.6k times · Source

I am making a WPF application that is navigable via custom "Next" and "Back" buttons and commands (i.e. not using a NavigationWindow). On one screen, I have a ListBox that has to support multiple selections (using the Extended mode). I have a view model for this screen and store the selected items as a property, since they need to be maintained.

However, I am aware that the SelectedItems property of a ListBox is read-only. I have been trying to work around the issue using this solution here, but I have not been able to adopt it into my implementation. I found that I can't differentiate between when one or more elements are deselected and when I navigate between screens (NotifyCollectionChangedAction.Remove is raised in both cases, since technically all the selected items are deselected when navigating away from the screen). My navigation commands are located in a separate view model which manages the view models for each screen, so I can't put any implementation related to the view model with the ListBox in there.

I have found several other less elegant solutions, but none of these seem to enforce a two-way binding between the view model and the view.

Any help would be greatly appreciated. I can provide some of my source code if it would help to understand my problem.

Answer

Rachel picture Rachel · Jun 21, 2012

Try creating an IsSelected property on each of your data items and binding ListBoxItem.IsSelected to that property

<Style TargetType="{x:Type ListBoxItem}">
    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
</Style>

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