Changing WPF TreeView SelectedItem in SelectedItemChanged event

Question

I currently have a WPF Treeview with a structure of:

--> Group 1 (Hierarchical Group)
   ---> Group 2 (Hierarchical Group)
      ---> Item 1
      ---> Item 2
      ---> Item 3

I currently have a SelectedItemChanged event handler hooked up to this treeview like so

private void TreeViewControl_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{

     if (e.NewValue is Item)
     {
         Item item = e.NewValue as Item;
         if (Item != SelectedItem)
         {
             //keep SelectedItem in sync with Treeview.SelectedItem
             SelectedItem = e.NewValue as Item;
         }

     }
     else
     {
         //if the user tries to select an object that isn't an Item (i.e. a group) reselect the first Item in that group
         //This will then cause stack overflow in methods I've tried so far
     }
}

So my question is, how can I keep the SelectedItem of the treeview in sync with my SelectedItem property in my code behind and also how can I reselect an item if the user selects a group?

EDIT:

    <TreeView Grid.Row="1" Grid.RowSpan="2"
              ItemContainerStyle="{StaticResource StandardListStyle}"
              ItemTemplate="{StaticResource TreeViewItemTemplate}"
              BorderThickness="1,0,1,1"
              VerticalContentAlignment="Stretch"
              HorizontalAlignment="Stretch"
              ItemsSource="{Binding Teams}"
              SelectedItemChanged="TreeViewControl_SelectedItemChanged"
              Loaded="OnTreeViewLoaded"
              x:Name="TreeViewControl">

where:

Teams = List<HierachicalGroup>;

and where:

public class HierachicalGroup
{
    public virtual string Name { get; set; }
    public virtual HierachicalGroup[] Children { get; set; }
    public virtual HierachicalGroup Parent { get; set; }
}

and item is:

public class Item: HierachicalGroup
{
    public Domain Domain { get; set; }

    public override string Name
    {
        get
        {
            return Domain.DomainName;
        }
    }
}

Answer 1

In TreeView.SelectedItemChanged event, we get e.NewValue which is type of TreeViewItem, so I think you can use following code to select an item when it's group is selected.

var item = (e.NewValue as TreeViewItem);
if (item.Items.Count > 0)
{
    (item.Items[0] as TreeViewItem).IsSelected = true;
}

Answer 2

You haven't really shown enough for a solid answer, but you must have set a collection of some type as the TreeView.ItemsSource property. Therefore all of your items in that collection must be of that type, maybe a base type. You just need to make your SelectedItem property the same type as those items in the collection and then you could do this:

SelectedItem = e.NewValue as TypeOfItemsInCollection;

Or, you could just add a SelectedGroupItem property of type Group (or whatever you need) and do this:

if (e.NewValue is Item)
{
    SelectedItem = e.NewValue as Item;
}
else if (e.NewValue is Group)
{
    SelectedGroupItem = e.NewValue as Group;
}

Answer 3

Ok so this was a lot more complicated than I initially thought.

I used this link for help: WPT TreeView ViewModel Pattern

    <TreeView Grid.Row="1" Grid.RowSpan="2"
              ItemTemplate="{StaticResource TreeViewItemTemplate}"
              BorderThickness="1,0,1,1"
              VerticalContentAlignment="Stretch"
              HorizontalAlignment="Stretch"
              ItemsSource="{Binding Teams}"
              SelectedItemChanged="TreeViewControl_SelectedItemChanged"
              Loaded="OnTreeViewLoaded"
              x:Name="TreeViewControl">
        <TreeView.ItemContainerStyle>
            <Style TargetType="{x:Type TreeViewItem}">
                <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
                <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
                <Setter Property="FontWeight" Value="Normal" />
                <Style.Triggers>
                    <Trigger Property="IsSelected" Value="True">
                        <Setter Property="FontWeight" Value="Bold" />
                    </Trigger>
                </Style.Triggers>
            </Style>
        </TreeView.ItemContainerStyle>
    </TreeView>

Where:

 public class HierachicalGroup: INotifyPropertyChanged
    {
        public virtual string Name { get; set; }
        public virtual HierachicalGroup[] Children { get; set; }
        public virtual HierachicalGroup Parent { get; set; }

        private bool _isSelected;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                if (value != _isSelected)
                {
                    _isSelected = value;
                    this.OnPropertyChanged("IsSelected");
                }
            }
        }


        private bool _isExpanded;
        public bool IsExpanded
        {
            get { return _isExpanded; }
            set
            {
                if (value != _isExpanded)
                {
                    _isExpanded = value;
                    this.OnPropertyChanged("IsExpanded");
                }

                // Expand all the way up to the root.
                if (_isExpanded && Parent != null)
                    Parent.IsExpanded = true;
            }
        }


        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        #endregion // INotifyPropertyChanged Members
   }

and:

 public class Item: HierachicalGroup, INotifyPropertyChanged
    {
        public Domain Domain { get; set; }

        public override string Name
        {
            get
            {
                return Domain.DomainName;
            }
            set
            {
                //not doing it :)
            }
        }

        private bool _isSelected;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                if (value != _isSelected)
                {
                    _isSelected = value;
                    this.OnPropertyChanged("IsSelected");
                }
            }
        }

        private void OnPropertyChanged(PropertyChangedEventArgs e)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, e);
        }



        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

and Finally:

    private void TreeViewControl_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {

        if (e.NewValue is Item)
        {
            Item item = e.NewValue as Item;
            if (Item != SelectedItem)
            {
                //keep SelectedItem in sync with Treeview.SelectedItem
                SelectedItem = e.NewValue as Item;
            }

        }
        else
        {
            var item = e.NewValue as HierarchicalGroup;
            item.IsExpanded = true;
            if (item.Children.Count() > 0)
            {
                if (item.Children[0] is Item)
                {
                    (item.Children[0] as Item).IsSelected = true;
                }
            }
        }
    }