Get TreeView SelectedItem inside ViewModel

Question

I'm trying to get selected TreeView Node inside ViewModel

Inside Xaml

<Grid>
        <TreeView ItemsSource="{Binding TreeViewModel.TreeData}">
            <TreeView.Resources>
                <HierarchicalDataTemplate ItemsSource="{Binding  GroupTables}" DataType="{x:Type tbl:StaticTablesGroup}">
                    <Label Content="{Binding Name}"/>

                </HierarchicalDataTemplate>

                <DataTemplate DataType="{x:Type tbl:GroupTable}">
                    <Label Content="{Binding Name}"/>
                </DataTemplate>
            </TreeView.Resources>

            <TreeView.ItemContainerStyle>
                <Style TargetType="TreeViewItem">
                    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
                    <Style.Triggers>
                        <Trigger Property="IsSelected" Value="True">
                            <Setter Property="FontWeight" Value="Bold" />
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </TreeView.ItemContainerStyle>
        </TreeView>        
    </Grid>

Inside VieModel

public class TreeTablesViewModel : ViewModelBase
    {
        private TablesXML _tables;
        public TreeTablesViewModel()
        {

            _tables = Deserialize.GuymasterXml();
        }

        public List<StaticTablesGroup> TreeData
        {
            get
            {
                return _tables.StaticTablesGroups;
            }

            set
            {
                _tables.StaticTablesGroups = value;
                OnPropertyChanged("TreeData");
            }
        }       
    }

and finally data classes

[XmlRoot("Tables")]
    public class TablesXML
    {
        public TablesXML()
        {
            StaticTablesGroups = new List<StaticTablesGroup>();
        }


        [XmlArray("StaticGroups")]
        [XmlArrayItem("StaticGroup", typeof(StaticTablesGroup))]
        public List<StaticTablesGroup> StaticTablesGroups { get; set; }

    }

    public class StaticTablesGroup
    {
        public StaticTablesGroup()
        {
            GroupTables = new List<GroupTable>();
        }

        [XmlAttribute("Name")]
        public string Name { get; set; }

        //[XmlArray("StaticGroup")]
        [XmlElement("Table", typeof(GroupTable))]
        public List<GroupTable> GroupTables { get; set; }


    }


    public class GroupTable
    {

        [XmlElement("TableName")]
        public string Name { get; set; }
        [XmlElement("TableTag")]
        public string Tag { get; set; }

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

                }
            }
        }
    }

When Treeview node is selected then IsSelected raised inside GroupTable or StaticTablesGroup. How can I get selected node inside the TreeTablesViewModel ?

Thank you

Answer 1

You should not try to manipulate view objects (TreeView, TreeViewItem, TreeNode, etc.) inside your view model. You view model must manipulate only business/poco objects.

If you want to retreive the underlying business object corresponding to the selected visual object (TreeViewItem or node), you can use a behavior like this one :

public class TreeviewSelectedItemTracker
{
    public static TreeTablesViewModel GetSelectedItemHolder(DependencyObject obj)
    {
        return (TreeTablesViewModel)obj.GetValue(SelectedItemHolderProperty);
    }

    public static void SetSelectedItemHolder(DependencyObject obj, TreeTablesViewModel value)
    {
        obj.SetValue(SelectedItemHolderProperty, value);
    }

    public static readonly DependencyProperty SelectedItemHolderProperty =
        DependencyProperty.RegisterAttached("SelectedItemHolder", typeof(TreeTablesViewModel), typeof(TreeviewSelectedItemTracker), new PropertyMetadata(null, OnSelectedChanged));

    private static void OnSelectedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        TreeView tv = (TreeView)d;
        tv.Loaded += Tv_Loaded;
    }

    private static void Tv_Loaded(object sender, RoutedEventArgs e)
    {
        TreeView tv = (TreeView)sender;
        tv.Loaded -= Tv_Loaded;
        tv.Unloaded += Tv_Unloaded;
        tv.SelectedItemChanged += Tv_SelectedItemChanged;
    }

    private static void Tv_Unloaded(object sender, RoutedEventArgs e)
    {
        TreeView tv = (TreeView)sender;

        tv.Unloaded -= Tv_Unloaded;
        tv.SelectedItemChanged -= Tv_SelectedItemChanged;
    }

    private static void Tv_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        TreeView tv = (TreeView)sender;

        var cotr = GetSelectedItemHolder(tv);

        cotr.SelectedItem = tv.SelectedItem;

    }
}

The TreeView.SelectedItem directly returns the business object associated with Selected TreeviewItem.

In the xaml, use the attached property to bind the SelectedItemHolder to your view model

<TreeView ItemsSource="{Binding TreeViewModel.TreeData}" local:TreeviewSelectedItemTracker.SelectedItemHolder="{Binding}"/>

Answer 2

The easiest way to get the TreeViewItem (which is what I think you mean) is to get it from the item container generator in the selection handler for the tree.

    private void treeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        TreeView tv = e.Source as TreeView;
        TreeViewItem tvi = tv.ItemContainerGenerator.ContainerFromItem(e.NewValue) as TreeViewItem;
    }

The XAML

    <TreeView ItemsSource="{Binding TreeViewModel.TreeData}" SelectedItemChanged="treeView_SelectedItemChanged" >

From here I think you can get to the view model.