Radical “Handle” behavior

Imagine that you need to handle from the ViewModel the SelectedIndexChanged of a WPF TreeView, currently the only way (without using any particular framework) is to build your own Behavior to achieve that, or bind, via a style the IsSelected property of the node to a property of the view model, but in this second case the side effect is that to find the selected item you need to visit the whole tree.

Enter Radical “Handle”

<TreeView Margin="5"
          HorizontalAlignment="Stretch" 
          VerticalAlignment="Stretch" 
          ItemsSource="{Binding Path=Accounts}">
    <i:Interaction.Behaviors>
        <behaviors:Handle RoutedEvent="TreeView.SelectedItemChanged" 
                    WithCommand="{Binding Path=SelectOutlookPath}"
                    PassingIn="$args.NewValue" />
    </i:Interaction.Behaviors>
    <TreeView.ItemTemplate>
        <!-- omitted -->
    </TreeView.ItemTemplate>
</TreeView>

As you can imagine the value of the NewValue property of the event arguments is passed as the command parameter to the command, we currently support to placeholder:

• $args: the routed event arguments;
• $this: the WPF element the behavior is attached to;
• $source: the source of the routed event;
• $originalSource: the original source of the routed event;

Obviously the event we need to handle must be a RoutedEvent.

Available in the Nuget package “Radical.Windows”

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