Data binding to SelectedItem in a WPF Treeview

Question

How can I retrieve the item that is selected in a WPF-treeview  I want to do this in XAML  because I want to bind it   You might think that it is SelectedItem but apparently that does not exist is readonly and therefore unusable   This is what I want to do    lt TreeView ItemsSource   Binding Path Model Clusters                ItemTemplate   StaticResource ClusterTemplate               SelectedItem   Binding Path Model SelectedCluster     gt    I want to bind the SelectedItem to a property on my Model   But this gives me the error       SelectedItem  property is read-only and cannot be set from markup    Edit  Ok  this is the way that I solved this    lt TreeView           ItemsSource   Binding Path Model Clusters              ItemTemplate   StaticResource HoofdCLusterTemplate             SelectedItemChanged  TreeView OnSelectedItemChanged    gt    and in the codebehindfile of my xaml   private void TreeView OnSelectedItemChanged object sender  RoutedPropertyChangedEventArgs lt object gt  e        Model SelectedCluster    Cluster e NewValue

User · Answer

I suggest an addition to the behavior provided by Steve Greatrex. His behavior doesn't reflects changes from the source because it may not be a collection of TreeViewItems. So it is a matter of finding the TreeViewItem in the tree which datacontext is the selectedValue from the source. The TreeView has a protected property called "ItemsHost", which holds the TreeViewItem collection. We can get it through reflection and walk the tree searching for the selected item.

private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        var behavior = sender as BindableSelectedItemBehaviour;

        if (behavior == null) return;

        var tree = behavior.AssociatedObject;

        if (tree == null) return;

        if (e.NewValue == null) 
            foreach (var item in tree.Items.OfType<TreeViewItem>())
                item.SetValue(TreeViewItem.IsSelectedProperty, false);

        var treeViewItem = e.NewValue as TreeViewItem; 
        if (treeViewItem != null)
        {
            treeViewItem.SetValue(TreeViewItem.IsSelectedProperty, true);
        }
        else
        {
            var itemsHostProperty = tree.GetType().GetProperty("ItemsHost", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

            if (itemsHostProperty == null) return;

            var itemsHost = itemsHostProperty.GetValue(tree, null) as Panel;

            if (itemsHost == null) return;

            foreach (var item in itemsHost.Children.OfType<TreeViewItem>())
                if (WalkTreeViewItem(item, e.NewValue)) break;
        }
    }

    public static bool WalkTreeViewItem(TreeViewItem treeViewItem, object selectedValue) {
        if (treeViewItem.DataContext == selectedValue)
        {
            treeViewItem.SetValue(TreeViewItem.IsSelectedProperty, true);
            treeViewItem.Focus();
            return true;
        }

        foreach (var item in treeViewItem.Items.OfType<TreeViewItem>())
            if (WalkTreeViewItem(item, selectedValue)) return true;

        return false;
    }

This way the behavior works for two-way bindings. Alternatively, it is possible to move the ItemsHost acquisition to the Behavior's OnAttached method, saving the overhead of using reflection every time the binding updates.

User · Answer

This can be accomplished in a  nicer  way using only binding and the GalaSoft MVVM Light library s EventToCommand  In your VM add a command which will be called when the selected item is changed  and initialize the command to perform whatever action is necessary  In this example I used a RelayCommand and will just set the SelectedCluster property   public class ViewModel       public ViewModel                 SelectedClusterChanged   new RelayCommand lt Cluster gt   c   gt  SelectedCluster   c               public RelayCommand lt Cluster gt  SelectedClusterChanged   get  private set          public Cluster SelectedCluster   get  private set        Then add the EventToCommand behavior in your xaml  This is really easy using blend    lt TreeView       x Name  lstClusters        ItemsSource   Binding Path Model Clusters          ItemTemplate   StaticResource HoofdCLusterTemplate   gt       lt i Interaction Triggers gt           lt i EventTrigger EventName  SelectedItemChanged  gt               lt GalaSoft MvvmLight Command EventToCommand Command   Binding SelectedClusterChanged   CommandParameter   Binding ElementName lstClusters Path SelectedValue    gt           lt  i EventTrigger gt       lt  i Interaction Triggers gt   lt  TreeView gt

User · Answer

I propose this solution  which I consider the easiest and memory leaks free  which works perfectly for updating the ViewModel s selected item from the View s selected item   Please note that changing the selected item from the ViewModel won t update the selected item of the View   public class TreeViewEx   TreeView       public static readonly DependencyProperty SelectedItemExProperty   DependencyProperty Register  SelectedItemEx   typeof object   typeof TreeViewEx   new FrameworkPropertyMetadata default object                 BindsTwoWayByDefault   true    Required in order to avoid setting the  BindingMode  from the XAML              public object SelectedItemEx               get   gt  GetValue SelectedItemExProperty           set   gt  SetValue SelectedItemExProperty  value              protected override void OnSelectedItemChanged RoutedPropertyChangedEventArgs lt object gt  e                SelectedItemEx   e NewValue            XAML usage   lt l TreeViewEx ItemsSource   Binding Path Items   SelectedItemEx   Binding Path SelectedItem    gt

User · Answer

Let s just all agree that TreeView is obviously busted in respect to this problem   Binding to SelectedItem would have been obvious   Sigh   I needed the solution to interact properly with the IsSelected property of TreeViewItem  so here s how I did it      the Type CustomThing needs to implement IsSelected with notification    for this to work  public class CustomTreeView   TreeView       public CustomThing SelectedCustomThing               get                       return  CustomThing GetValue SelectedNode Property                     set                       SetValue SelectedNode Property  value               if value    null  value IsSelected   true                       public static DependencyProperty SelectedNode Property           DependencyProperty Register               SelectedCustomThing               typeof CustomThing               typeof CustomTreeView               new FrameworkPropertyMetadata                  null                  FrameworkPropertyMetadataOptions None                  SelectedNodeChanged         public CustomTreeView    base                 this SelectedItemChanged    new RoutedPropertyChangedEventHandler lt object gt  SelectedItemChanged CustomHandler              void SelectedItemChanged CustomHandler object sender  RoutedPropertyChangedEventArgs lt object gt  e                SetValue SelectedNode Property  SelectedItem              private static void SelectedNodeChanged DependencyObject d  DependencyPropertyChangedEventArgs e                var treeView   d as CustomTreeView          var newNode   e NewValue as CustomThing           treeView SelectedCustomThing    CustomThing e NewValue            With this XAML    lt local CustonTreeView ItemsSource   Binding TreeRoot        SelectedCustomThing   Binding SelectedNode Mode TwoWay   gt       lt TreeView ItemContainerStyle gt           lt Style TargetType  TreeViewItem  gt               lt Setter Property  IsSelected  Value   Binding IsSelected  Mode TwoWay     gt           lt  Style gt       lt  TreeView ItemContainerStyle gt   lt  local CustonTreeView gt

User · Answer

Answer with attached properties and no external dependencies  should the need ever arise   You can create an attached property that is bindable and has a getter and setter   public class TreeViewHelper       private static Dictionary lt DependencyObject  TreeViewSelectedItemBehavior gt  behaviors   new Dictionary lt DependencyObject  TreeViewSelectedItemBehavior gt          public static object GetSelectedItem DependencyObject obj                return  object obj GetValue SelectedItemProperty              public static void SetSelectedItem DependencyObject obj  object value                obj SetValue SelectedItemProperty  value                 Using a DependencyProperty as the backing store for SelectedItem   This enables animation  styling  binding  etc        public static readonly DependencyProperty SelectedItemProperty           DependencyProperty RegisterAttached  SelectedItem   typeof object   typeof TreeViewHelper   new UIPropertyMetadata null  SelectedItemChanged         private static void SelectedItemChanged DependencyObject obj  DependencyPropertyChangedEventArgs e                if    obj is TreeView               return           if   behaviors ContainsKey obj               behaviors Add obj  new TreeViewSelectedItemBehavior obj as TreeView             TreeViewSelectedItemBehavior view   behaviors obj           view ChangeSelectedItem e NewValue              private class TreeViewSelectedItemBehavior               TreeView view          public TreeViewSelectedItemBehavior TreeView view                        this view   view              view SelectedItemChanged     sender  e    gt  SetSelectedItem view  e NewValue                      internal void ChangeSelectedItem object p                        TreeViewItem item    TreeViewItem view ItemContainerGenerator ContainerFromItem p               item IsSelected   true                      Add the namespace declaration containing that class to your XAML and bind as follows  local is how I named the namespace declaration             lt TreeView ItemsSource   Binding Path Root Children   local TreeViewHelper SelectedItem   Binding Path SelectedItem  Mode TwoWay   gt        lt  TreeView gt    Now you can bind the selected item  and also set it in your view model to change it programmatically  should that requirement ever arise  This is  of course  assuming that you implement INotifyPropertyChanged on that particular property

User · Answer

Well  I found a solution  It moves the mess  so that MVVM works   First add this class   public class ExtendedTreeView   TreeView       public ExtendedTreeView             base                 this SelectedItemChanged    new RoutedPropertyChangedEventHandler lt object gt     ICH              void    ICH object sender  RoutedPropertyChangedEventArgs lt object gt  e                if  SelectedItem    null                        SetValue SelectedItem Property  SelectedItem                        public object SelectedItem                get   return  object GetValue SelectedItem Property             set   SetValue SelectedItem Property  value               public static readonly DependencyProperty SelectedItem Property   DependencyProperty Register  SelectedItem    typeof object   typeof ExtendedTreeView   new UIPropertyMetadata null        and add this to your xaml     lt local ExtendedTreeView ItemsSource   Binding Items   SelectedItem    Binding Item  Mode TwoWay   gt           lt  local ExtendedTreeView gt

User · Answer

All to complicated     Go with Caliburn Micro  http   caliburnmicro codeplex com    View    lt TreeView Micro Message Attach   Event SelectedItemChanged     Action SetSelectedItem  this SelectedItem      gt    ViewModel   public void SetSelectedItem YourNodeViewModel item

User · Answer

WPF MVVM TreeView SelectedItem      is a better answer  but does not mention a way to get set the SelectedItem in the ViewModel     Add a IsSelected boolean property to your ItemViewModel  and bind to it in a Style Setter for the TreeViewItem   Add a SelectedItem property to your ViewModel used as the DataContext for the TreeView  This is the missing piece in the solution above           ItemVM        Public Property IsSelected As Boolean         Get             Return  func SelectedNode Is Me         End Get         Set value As Boolean              If IsSelected  value Then                  func SelectedNode   If value  Me  Nothing              End If             RaisePropertyChange           End Set     End Property       TreeVM        Public Property SelectedItem As ItemVM         Get             Return  selectedItem         End Get         Set value As ItemVM              If  selectedItem Is value Then                 Return             End If             Dim prev    selectedItem              selectedItem   value             If prev IsNot Nothing Then                 prev IsSelected   False             End If             If  selectedItem IsNot Nothing Then                  selectedItem IsSelected   True             End If         End Set     End Property    lt TreeView ItemsSource   Binding Path TreeVM              BorderBrush  Transparent  gt       lt TreeView ItemContainerStyle gt           lt Style TargetType  TreeViewItem  gt               lt Setter Property  IsExpanded  Value   Binding IsExpanded    gt               lt Setter Property  IsSelected  Value   Binding IsSelected  Mode TwoWay    gt           lt  Style gt       lt  TreeView ItemContainerStyle gt       lt TreeView ItemTemplate gt           lt HierarchicalDataTemplate ItemsSource   Binding Children   gt               lt TextBlock Text   Binding Name    gt           lt  HierarchicalDataTemplate gt       lt  TreeView ItemTemplate gt   lt  TreeView gt

User · Answer

I came across this page looking for the same answer as the original author  and proving there s always more than one way to do it  the solution for me was even easier than the answers provided here so far  so I figured I might as well add to the pile   The motivation for the binding is to keep it nice  amp  MVVM  The probable usage of the ViewModel is to have a property w  a name such as  CurrentThingy   and somewhere else  the DataContext on some other thing is bound to  CurrentThingy    Rather than going through additional steps required  eg  custom behavior  3rd party control  to support a nice binding from the TreeView to my Model  and then from something else to my Model  my solution was to use simple Element binding the other thing to TreeView SelectedItem  rather than binding the other thing to my ViewModel  thereby skipping the extra work required   XAML    lt TreeView x Name  myTreeView  ItemsSource   Binding MyThingyCollection   gt       stuff  lt  TreeView gt    lt  -- then   somewhere else where I want to see the currently selected TreeView item  -- gt    lt local MyThingyDetailsView         DataContext   Binding ElementName myTreeView  Path SelectedItem     gt    Of course  this is great for reading the currently selected item  but not setting it  which is all I needed

User · Answer

It can also be done using the IsSelected property of the TreeView item  Here s how I managed it   public delegate void TreeviewItemSelectedHandler TreeViewItem item   public class TreeViewItem           public static event TreeviewItemSelectedHandler OnItemSelected   delegate        public bool IsSelected          get   return isSelected        set               isSelected   value        if  value          OnItemSelected this                 Then in the ViewModel that contains the data your TreeView is bound to  just subscribe to the event in the TreeViewItem class   TreeViewItem OnItemSelected    TreeViewItemSelected    And finally  implement this handler in the same ViewModel   private void TreeViewItemSelected TreeViewItem item        Do something     And the binding of course    lt Setter Property  IsSelected  Value   Binding IsSelected     gt

User · Answer

This property exists   TreeView SelectedItem  But it is readonly  so you cannot assign it through a binding  only retrieve it

User · Answer

You might also be able to use TreeViewItem IsSelected property

User · Answer

I bring you my solution which offers the following features    Supports 2 ways binding Auto updates the TreeViewItem IsSelected properties  according to the SelectedItem  No TreeView subclassing Items bound to ViewModel can be of any type  even null    1  Paste the following code in your CS   public class BindableSelectedItem       public static readonly DependencyProperty SelectedItemProperty   DependencyProperty RegisterAttached           SelectedItem   typeof object   typeof BindableSelectedItem   new PropertyMetadata default object   OnSelectedItemPropertyChangedCallback         private static void OnSelectedItemPropertyChangedCallback DependencyObject d  DependencyPropertyChangedEventArgs e                var treeView   d as TreeView          if  treeView    null                        BrowseTreeViewItems treeView  tvi   gt                                tvi IsSelected   tvi DataContext    e NewValue                                    else                       throw new Exception  Attached property supports only TreeView                         public static void SetSelectedItem DependencyObject element  object value                element SetValue SelectedItemProperty  value              public static object GetSelectedItem DependencyObject element                return element GetValue SelectedItemProperty              public static void BrowseTreeViewItems TreeView treeView  Action lt TreeViewItem gt  onBrowsedTreeViewItem                var collectionsToVisit   new System Collections Generic List lt Tuple lt ItemContainerGenerator  ItemCollection gt  gt    new Tuple lt ItemContainerGenerator  ItemCollection gt  treeView ItemContainerGenerator  treeView Items             var collectionIndex   0          while  collectionIndex  lt  collectionsToVisit Count                        var itemContainerGenerator   collectionsToVisit collectionIndex  Item1              var itemCollection   collectionsToVisit collectionIndex  Item2              for  var i   0  i  lt  itemCollection Count  i                                  var tvi   itemContainerGenerator ContainerFromIndex i  as TreeViewItem                  if  tvi    null                                        continue                                     if  tvi ItemContainerGenerator Status    System Windows Controls Primitives GeneratorStatus ContainersGenerated                                        collectionsToVisit Add new Tuple lt ItemContainerGenerator  ItemCollection gt  tvi ItemContainerGenerator  tvi Items                                       onBrowsedTreeViewItem tvi                              collectionIndex                         2  Example of use in your XAML file   lt TreeView myNS BindableSelectedItem SelectedItem   Binding Path SelectedItem  Mode TwoWay     gt

User · Answer

I know this thread is 10 years old but the problem still exists      The original question was  to retrieve  the selected item  I also needed to  get  the selected item in my viewmodel  not set it   Of all the answers in this thread  the one by  Wes  is the only one that approaches the problem differently  If you can use the  Selected Item  as a target for databinding use it as a source for databinding  Wes did it to another view property  I will do it to a viewmodel property   We need two things    Create a dependency property in the viewmodel  in my case of type  MyObject  as my treeview is bound to object of the  MyObject  type  Bind from the Treeview SelectedItem to this property in the View s constructor  yes that is code behind but  it s likely that you will init your datacontext there as well    Viewmodel   public static readonly DependencyProperty SelectedTreeViewItemProperty   DependencyProperty Register  SelectedTreeViewItem   typeof MyObject   typeof MyViewModel   new PropertyMetadata OnSelectedTreeViewItemChanged         private static void OnSelectedTreeViewItemChanged DependencyObject d  DependencyPropertyChangedEventArgs e                 d as MyViewModel  OnSelectedTreeViewItemChanged e              private void OnSelectedTreeViewItemChanged DependencyPropertyChangedEventArgs e                  do your stuff here            public MyObject SelectedWorkOrderTreeViewItem               get   return  MyObject GetValue SelectedTreeViewItemProperty             set   SetValue SelectedTreeViewItemProperty  value             View constructor   Binding binding   new Binding  SelectedItem                         Source   treeView    name of tree view in xaml             Mode   BindingMode OneWay                     BindingOperations SetBinding DataContext  MyViewModel SelectedTreeViewItemProperty  binding

User · Answer

There is also a way to create XAML bindable SelectedItem property without using Interaction Behaviors   public static class BindableSelectedItemHelper        region Properties      public static readonly DependencyProperty SelectedItemProperty   DependencyProperty RegisterAttached  SelectedItem   typeof object   typeof BindableSelectedItemHelper           new FrameworkPropertyMetadata null  OnSelectedItemPropertyChanged         public static readonly DependencyProperty AttachProperty   DependencyProperty RegisterAttached  Attach   typeof bool   typeof BindableSelectedItemHelper   new PropertyMetadata false  Attach         private static readonly DependencyProperty IsUpdatingProperty   DependencyProperty RegisterAttached  IsUpdating   typeof bool   typeof BindableSelectedItemHelper          endregion       region Implementation      public static void SetAttach DependencyObject dp  bool value                dp SetValue AttachProperty  value              public static bool GetAttach DependencyObject dp                return  bool dp GetValue AttachProperty              public static string GetSelectedItem DependencyObject dp                return  string dp GetValue SelectedItemProperty              public static void SetSelectedItem DependencyObject dp  object value                dp SetValue SelectedItemProperty  value              private static bool GetIsUpdating DependencyObject dp                return  bool dp GetValue IsUpdatingProperty              private static void SetIsUpdating DependencyObject dp  bool value                dp SetValue IsUpdatingProperty  value              private static void Attach DependencyObject sender  DependencyPropertyChangedEventArgs e                TreeListView treeListView   sender as TreeListView          if  treeListView    null                        if   bool e OldValue                  treeListView SelectedItemChanged -  SelectedItemChanged               if   bool e NewValue                  treeListView SelectedItemChanged    SelectedItemChanged                       private static void OnSelectedItemPropertyChanged DependencyObject sender  DependencyPropertyChangedEventArgs e                TreeListView treeListView   sender as TreeListView          if  treeListView    null                        treeListView SelectedItemChanged -  SelectedItemChanged               if    bool GetIsUpdating treeListView                                 foreach  TreeViewItem item in treeListView Items                                        if  item    e NewValue                                                item IsSelected   true                          break                                            else                        item IsSelected   false                                                                       treeListView SelectedItemChanged    SelectedItemChanged                       private static void SelectedItemChanged object sender  RoutedEventArgs e                TreeListView treeListView   sender as TreeListView          if  treeListView    null                        SetIsUpdating treeListView  true               SetSelectedItem treeListView  treeListView SelectedItem               SetIsUpdating treeListView  false                        endregion     You can then use this in your XAML as    lt TreeView  helper BindableSelectedItemHelper Attach  True              helper BindableSelectedItemHelper SelectedItem   Binding SelectedItem  Mode TwoWay   gt

User · Answer

I realise this has already had an answer accepted  but I put this together to solve the problem   It uses a similar idea to Delta s solution  but without the need to subclass the TreeView   public class BindableSelectedItemBehavior   Behavior lt TreeView gt         region SelectedItem Property      public object SelectedItem               get   return  object GetValue SelectedItemProperty             set   SetValue SelectedItemProperty  value                public static readonly DependencyProperty SelectedItemProperty           DependencyProperty Register  SelectedItem   typeof object   typeof BindableSelectedItemBehavior   new UIPropertyMetadata null  OnSelectedItemChanged         private static void OnSelectedItemChanged DependencyObject sender  DependencyPropertyChangedEventArgs e                var item   e NewValue as TreeViewItem          if  item    null                        item SetValue TreeViewItem IsSelectedProperty  true                         endregion      protected override void OnAttached                 base OnAttached             this AssociatedObject SelectedItemChanged    OnTreeViewSelectedItemChanged             protected override void OnDetaching                 base OnDetaching             if  this AssociatedObject    null                        this AssociatedObject SelectedItemChanged -  OnTreeViewSelectedItemChanged                       private void OnTreeViewSelectedItemChanged object sender  RoutedPropertyChangedEventArgs lt object gt  e                this SelectedItem   e NewValue            You can then use this in your XAML as    lt TreeView gt       lt e Interaction Behaviors gt           lt behaviours BindableSelectedItemBehavior SelectedItem   Binding SelectedItem  Mode TwoWay     gt       lt  e Interaction Behaviors gt   lt  TreeView gt    Hopefully it will help someone

User · Answer

I tried all solutions of this questions  No one solved my problem fully  So I think it s better to use such inherited class with redefined property SelectedItem  It will work perfectly if you choose tree element from GUI and if you set this property value in your code  public class TreeViewEx   TreeView       public TreeViewEx                 this SelectedItemChanged    new RoutedPropertyChangedEventHandler lt object gt  TreeViewEx SelectedItemChanged              void TreeViewEx SelectedItemChanged object sender  RoutedPropertyChangedEventArgs lt object gt  e                this SelectedItem   e NewValue              region SelectedItem           lt summary gt          Gets or Sets the SelectedItem possible Value of the TreeViewItem object           lt  summary gt      public new object SelectedItem               get   return this GetValue TreeViewEx SelectedItemProperty             set   this SetValue TreeViewEx SelectedItemProperty  value                   Using a DependencyProperty as the backing store for MyProperty   This enables animation  styling  binding  etc        public new static readonly DependencyProperty SelectedItemProperty           DependencyProperty Register  SelectedItem   typeof object   typeof TreeViewEx           new FrameworkPropertyMetadata null  FrameworkPropertyMetadataOptions BindsTwoWayByDefault  SelectedItemProperty Changed         static void SelectedItemProperty Changed DependencyObject dependencyObject  DependencyPropertyChangedEventArgs e                TreeViewEx targetObject   dependencyObject as TreeViewEx          if  targetObject    null                        TreeViewItem tvi   targetObject FindItemNode targetObject SelectedItem  as TreeViewItem              if  tvi    null                  tvi IsSelected   true                                                                      endregion SelectedItem         public TreeViewItem FindItemNode object item                TreeViewItem node   null          foreach  object data in this Items                        node   this ItemContainerGenerator ContainerFromItem data  as TreeViewItem              if  node    null                                if  data    item                      break                  node   FindItemNodeInChildren node  item                   if  node    null                      break                                  return node             protected TreeViewItem FindItemNodeInChildren TreeViewItem parent  object item                TreeViewItem node   null          bool isExpanded   parent IsExpanded          if   isExpanded    Can t find child container unless the parent node is Expanded once                       parent IsExpanded   true              parent UpdateLayout                      foreach  object data in parent Items                        node   parent ItemContainerGenerator ContainerFromItem data  as TreeViewItem              if  data    item  amp  amp  node    null                  break              node   FindItemNodeInChildren node  item               if  node    null                  break                    if  node    null  amp  amp  parent IsExpanded    isExpanded              parent IsExpanded   isExpanded          if  node    null              parent IsExpanded   true          return node

User · Answer

After studying the Internet for a day I found my own solution for selecting an item after create a normal treeview in a normal WPF C  environment  private void BuildSortTree int sel                        MergeSort Items Clear                TreeViewItem itTemp   new TreeViewItem                itTemp Header   SortList 0               MergeSort Items Add itTemp               TreeViewItem prev              itTemp IsExpanded   true              if  0    sel  itTemp IsSelected  true              prev   itTemp              for int i   1  i lt SortList Count  i                                   TreeViewItem itTempNEW   new TreeViewItem                    itTempNEW Header   SortList i                   prev Items Add itTempNEW                   itTempNEW IsExpanded   true                  if  i    sel  itTempNEW IsSelected   true                  prev   itTempNEW

User · Answer

It answers a little more than the OP is expecting    But I hope it could help some one at least   If you want to execute a ICommand whenever the SelectedItem changed  you can bind a command on an event and the use of a property SelectedItem in the ViewModel isn t needed anymore   To do so   1- Add reference to System Windows Interactivity  xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity    2- Bind the command to the event SelectedItemChanged   lt TreeView x Name  myTreeView  Margin  1              ItemsSource   Binding Directories   gt       lt i Interaction Triggers gt           lt i EventTrigger EventName  SelectedItemChanged  gt               lt i InvokeCommandAction Command   Binding SomeCommand                                      CommandParameter                                                Binding ElementName myTreeView                                               Path SelectedItem    gt           lt  i EventTrigger gt       lt  i Interaction Triggers gt       lt TreeView ItemTemplate gt              lt  --     -- gt       lt  TreeView ItemTemplate gt   lt  TreeView gt

User · Answer

My requirement was for PRISM-MVVM based solution where a TreeView was needed and the bound object is of type Collection lt   and hence needs HierarchicalDataTemplate  The default BindableSelectedItemBehavior wont be able to identify the child TreeViewItem  To make it to work in this scenario   public class BindableSelectedItemBehavior   Behavior lt TreeView gt         region SelectedItem Property      public object SelectedItem               get   return  object GetValue SelectedItemProperty             set   SetValue SelectedItemProperty  value                public static readonly DependencyProperty SelectedItemProperty           DependencyProperty Register  SelectedItem   typeof object   typeof BindableSelectedItemBehavior   new UIPropertyMetadata null  OnSelectedItemChanged         private static void OnSelectedItemChanged DependencyObject sender  DependencyPropertyChangedEventArgs e                var behavior   sender as BindableSelectedItemBehavior          if  behavior    null  return          var tree   behavior AssociatedObject          if  tree    null  return          if  e NewValue    null              foreach  var item in tree Items OfType lt TreeViewItem gt                     item SetValue TreeViewItem IsSelectedProperty  false           var treeViewItem   e NewValue as TreeViewItem          if  treeViewItem    null              treeViewItem SetValue TreeViewItem IsSelectedProperty  true           else                       var itemsHostProperty   tree GetType   GetProperty  ItemsHost   System Reflection BindingFlags NonPublic   System Reflection BindingFlags Instance               if  itemsHostProperty    null  return              var itemsHost   itemsHostProperty GetValue tree  null  as Panel              if  itemsHost    null  return              foreach  var item in itemsHost Children OfType lt TreeViewItem gt                                   if  WalkTreeViewItem item  e NewValue                        break                                     public static bool WalkTreeViewItem TreeViewItem treeViewItem  object selectedValue                if  treeViewItem DataContext    selectedValue                        treeViewItem SetValue TreeViewItem IsSelectedProperty  true               treeViewItem Focus                return true                    var itemsHostProperty   treeViewItem GetType   GetProperty  ItemsHost   System Reflection BindingFlags NonPublic   System Reflection BindingFlags Instance           if  itemsHostProperty    null  return false          var itemsHost   itemsHostProperty GetValue treeViewItem  null  as Panel          if  itemsHost    null  return false          foreach  var item in itemsHost Children OfType lt TreeViewItem gt                           if  WalkTreeViewItem item  selectedValue                   break                    return false             endregion      protected override void OnAttached                 base OnAttached            this AssociatedObject SelectedItemChanged    OnTreeViewSelectedItemChanged             protected override void OnDetaching                 base OnDetaching            if  this AssociatedObject    null                        this AssociatedObject SelectedItemChanged -  OnTreeViewSelectedItemChanged                       private void OnTreeViewSelectedItemChanged object sender  RoutedPropertyChangedEventArgs lt object gt  e                this SelectedItem   e NewValue            This enables to iterate through all the elements irrespective of the level

[c#] Data binding to SelectedItem in a WPF Treeview

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