如何取消用户的WPF TreeView点击？

<TreeView.ItemContainerStyle>
   <Style TargetType="{x:Type TreeViewItem}">
       <Setter Property="Command" Value="{Binding DataContext.MyCommand, RelativeSource={RelativeSource AncestorType=TreeView}}" />
       <Setter Property="CommandParameter" Value="{Binding}" />
    </Style>
</TreeView.ItemContainerStyle>

public ICommand MyCommand { get; set; }

public MyViewModel()
{
    MyCommand = new RelayCommand<object>(ExecuteMyCommand);
}

private void ExecuteMyCommand(object parameter)
{
    // 处理点击事件
}

public class TreeViewItemBehavior
{
    public static ICommand GetCommand(DependencyObject obj)
    {
        return (ICommand)obj.GetValue(CommandProperty);
    }

    public static void SetCommand(DependencyObject obj, ICommand value)
    {
        obj.SetValue(CommandProperty, value);
    }

    public static readonly DependencyProperty CommandProperty =
        DependencyProperty.RegisterAttached("Command", typeof(ICommand), typeof(TreeViewItemBehavior), new UIPropertyMetadata(null, OnCommandChanged));

    private static void OnCommandChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        var item = sender as TreeViewItem;
        if (item == null)
            return;

        if (e.NewValue != null)
            item.PreviewMouseLeftButtonDown += OnItemPreviewMouseLeftButtonDown;
        else
            item.PreviewMouseLeftButtonDown -= OnItemPreviewMouseLeftButtonDown;
    }

    private static void OnItemPreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var item = sender as TreeViewItem;
        if (item == null)
            return;

        var command = GetCommand(item);
        if (command != null)
        {
            if (command.CanExecute(item.DataContext))
                command.Execute(item.DataContext);
        }
    }
}

<TreeView>
    <TreeView.ItemContainerStyle>
       <Style TargetType="{x:Type TreeViewItem}">
           <Setter Property="local:TreeViewItemBehavior.Command" Value="{Binding DataContext.MyCommand, RelativeSource={RelativeSource AncestorType=TreeView}}" />
        </Style>
    </TreeView.ItemContainerStyle>
</TreeView>