Question

I have a WPF ListBox in Extended SelectionMode.

What I need to do is bind the ListBox to an observable collection of a data item class, which is easy, but essentially, bind the IsSelected status of each ListBoxItem to a boolean property in the respective data item.

And, I need it to be two-way, so that I can populate the ListBox with selected and unselected items from the ViewModel.

I’ve looked at a number of implementations but none work for me. They include:

• Adding a DataTrigger to the ListBoxItem’s style and calling a state action change

I realise this can be done in code-behind with an event handler, but given the complexity of the domain it would be horribly messy. I’d rather stick to two-way Binding with the ViewModel.

Thanks.
Mark

Answer 1

In WPF you can easily bind your ListBox to a collection of items with a boolean property for the IsSelected state. If your question is about Silverlight, i’m afraid it won’t work the easy way.

public class Item : INotifyPropertyChanged
{
    // INotifyPropertyChanged stuff not shown here for brevity
    public string ItemText { get; set; }
    public bool IsItemSelected { get; set; }
}

public class ViewModel : INotifyPropertyChanged
{
    public ViewModel()
    {
        Items = new ObservableCollection<Item>();
    }

    // INotifyPropertyChanged stuff not shown here for brevity
    public ObservableCollection<Item> Items { get; set; }
}

---

<ListBox ItemsSource="{Binding Items, Source={StaticResource ViewModel}}"
         SelectionMode="Extended">
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="IsSelected" Value="{Binding IsItemSelected}"/>
        </Style>
    </ListBox.ItemContainerStyle>
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding ItemText}"/>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>