WPF selection of a TreeView item as context menu is called

Question

This problem relates mainly to context menus, but in my specific case it's about a TreeView control.

The TreeView item contains a StackPanel, and on that StackPanel is a ContextMenu property, which I have assigned to a StaticResource (which is a ContextMenu of course). Said ContextMenu leads to an ICommand and, thus, does its thing.

At present (and this is the default behaviour I believe), right clicking on an item in the TreeView does not select that item. This is common in Windows, but doesn't happen here. I would like it to happen (but I don't know how).

A little follow up information: I do have a selected item in the TreeView and this changes with a mouse left click. It's not a left click event, though, rather the event is 'SelectedItemChanged'. This leads to a method whereby I set the 'SelectedItem' in my data context (view model) to the SelectedItem. It has to be done this way because a TreeView's selected item is 'read only'.

That code is here, although I'm not sure how useful it is to the issue at hand:

private void TreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        if (this.ScenesTreeView01 == null)
            return;

        if (this.ScenesTreeView01.DataContext == null)
            return;

        var DataContext = this.ScenesTreeView01.DataContext as ScenesViewModel;

        if (e.NewValue is SceneViewModel)
        {
            DataContext.SelectedScene = (SceneViewModel)e.NewValue;
        }

        if (e.NewValue is CharacterViewModel)
        {

            DataContext.SelectedCharacter = (CharacterViewModel)e.NewValue;
        }
    }

Since there doesn't seem to be a place where it says 'okay you left clicked and so here is the selected item', I don't know what to do to tell it to assign the selected item on a right click (as well as a left click).

How can I do this?

Edit: I am using MVVM so when we have a method like SelectedItemChanged with a parameter which is RoutedPropertyChangedEventArgs e, e.Source refers me back to my view model, not to a TreeViewItem.

Answer 1

You could add an IsSelected property to your SceneViewModel and CharacterViewModel classes and bind the IsSelected of the TreeViewItem to these properties using a style. In the same style you could then hook up an event handler for the PreviewMouseRightButtonDown to set the source property:

<TreeView x:Name="treeView">
    <TreeView.Resources>
        <Style TargetType="TreeViewItem">
            <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
            <EventSetter Event="PreviewMouseRightButtonDown" Handler="treeView_PreviewMouseRightButtonDown" />
            <Setter Property="ContextMenu">
                <Setter.Value>
                    <ContextMenu>
                        <MenuItem>1</MenuItem>
                    </ContextMenu>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.Resources>
</TreeView>

---

private void treeView_PreviewMouseRightButtonDown(object sender, MouseButtonEventArgs e)
{
    TreeViewItem tvi = sender as TreeViewItem;
    CharacterViewModel cvm = tvi.DataContext as CharacterViewModel;
    if (cvm != null)
    {
        cvm.IsSelected = true;
    }
    else
    {
        SceneViewModel svm = tvi.DataContext as SceneViewModel;
        if (svm != null)
            svm.IsSelected = true;
    }
}

Make sure that the CharacterViewModel and SceneViewModel classes implement the INotifyPropertyChanged interface and raise the PropertyChanged event in the setter of the new IsSelected property.

Answer 2

A quick solution might be to simply register the TreeView's MouseRightButtonDown event, check if the click was on a TreeViewItem and select it:

TreeView.MouseRightButtonDown += Tv_MouseRightButtonDown;

void Tv_MouseRightButtonDown(object sender, MouseButtonEventArgs e) {
    var tvItem = e.Source as TreeViewItem;
    if (tvItem != null) {
        tvItem.IsSelected = true;
    }
}

Answer 3

You can use a behavior for it:

using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;

public class SelectOnRMBBehavior : Behavior<FrameworkElement>
{
    public static readonly DependencyProperty CurrentItemProperty = DependencyProperty.Register("CurrentItem", typeof(TreeViewItem), typeof(SelectOnRMBBehavior), new PropertyMetadata(null));

    public TreeViewItem CurrentItem
    {
        get
        {
            return (TreeViewItem)GetValue(CurrentItemProperty);
        }
        set
        {
            SetValue(CurrentItemProperty, value);
        }
    }

    protected override void OnAttached()
    {
        base.OnAttached();

        AssociatedObject.PreviewMouseRightButtonDown += AssociatedObject_PreviewMouseRightButtonDown;
    }

    private void AssociatedObject_PreviewMouseRightButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
    {
        if (CurrentItem!=null)
        {
            CurrentItem.IsSelected = true;
        }
    }

    protected override void OnDetaching()
    {
        AssociatedObject.PreviewMouseRightButtonDown -= AssociatedObject_PreviewMouseRightButtonDown;

        base.OnDetaching();
    }
}

and then just put your behavior to the element which will be clicked(I suppose a container in DataTemplate):

<StackPanel>
    <i:Interaction.Behaviors>
        <b:SelectOnRMBBehavior CurrentItem="{Binding RelativeSource={RelativeSource AncestorType=TreeViewItem}}"/>
    </i:Interaction.Behaviors>
</StackPanel>