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Creating Items DP for charting user control

I am busy creating a user control that has some basic charting/graph functions. In essence I want to have an "Items" dependency property to which the user of the control can bind. The control will then display all the items and updates made to the source.
What I have done so far was to create an "Items" DP in my user control, code behind.
public static readonly DependencyProperty ItemsProperty =
DependencyProperty.Register("Items",
typeof(ObservableCollection<Polyline>),
typeof(RPGraph),
new FrameworkPropertyMetadata(
new ObservableCollection<Polyline>(),
new PropertyChangedCallback(OnItemsChanged)));
public ObservableCollection<Polyline> Items
{
get { return (ObservableCollection<Polyline>)GetValue(ItemsProperty); }
set { SetValue(ItemsProperty, value); }
}
public static void OnItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
}
My first stumbling block was that "OnItemsChanged" didn't get called when my collection changed. After a couple of hours I found a stackoverflow post explaining why (ObservableCollection dependency property does not update when item in collection is deleted). Following this advice solved one part of my problem. Now I could Add new items (Polylines) to the ObservableCollection list. But what if I added an extra point or modified a point in the Polyline. Armed with the knowledge of the previous problem I found the Points.Changed event. I then subscribed to it and placed the update code in there.
This finally works, but man there must be a better or more elegant way of achieving this (as stated at the top), which I think all boils down to not using ObservableCollection? Any advice?
Below is the working OnItemChanged method (excuse the draft code, I just wanted to get it working :-) :
public static void OnItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var thisControl = d as RPGraph;
foreach (Polyline poly in thisControl.Items)
thisControl.manager.Items.Add(poly.Points.ToArray());
if (e.OldValue != null)
{
var coll = (INotifyCollectionChanged)e.OldValue;
// Unsubscribe from CollectionChanged on the old collection
coll.CollectionChanged -= Items_CollectionChanged;
}
if (e.NewValue != null)
{
var coll = (ObservableCollection<Polyline>)e.NewValue;
// Subscribe to CollectionChanged on the new collection
coll.CollectionChanged += (o, t) => {
ObservableCollection<Polyline> items = o as ObservableCollection<Polyline>;
thisControl.manager.Items.Add(items[t.NewStartingIndex].Points.ToArray());
foreach (Polyline poly in items)
{
poly.Points.Changed += (n, m) => {
for (int i = 0; i < thisControl.manager.Items.Count; i++)
thisControl.manager.Items[i] = thisControl.Items[i].Points.ToArray();
thisControl.manager.DrawGraph(thisControl.graphView);
};
}
thisControl.manager.DrawGraph(thisControl.graphView);
};
}
thisControl.manager.DrawGraph(thisControl.graphView);
}

You are completely right, an ObservableCollection does not notify when any of its items changes its property value.
You could extend the functionality of ObservableCollection adding notifications for these cases.
It may look like this:
public sealed class ObservableNotifiableCollection<T> : ObservableCollection<T> where T : INotifyPropertyChanged
{
public event ItemPropertyChangedEventHandler ItemPropertyChanged;
public event EventHandler CollectionCleared;
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
{
base.OnCollectionChanged(args);
if (args.NewItems != null)
{
foreach (INotifyPropertyChanged item in args.NewItems)
{
item.PropertyChanged += this.OnItemPropertyChanged;
}
}
if (args.OldItems != null)
{
foreach (INotifyPropertyChanged item in args.OldItems)
{
item.PropertyChanged -= this.OnItemPropertyChanged;
}
}
}
protected override void ClearItems()
{
foreach (INotifyPropertyChanged item in this.Items)
{
item.PropertyChanged -= this.OnItemPropertyChanged;
}
base.ClearItems();
this.OnCollectionCleared();
}
private void OnCollectionCleared()
{
EventHandler eventHandler = this.CollectionCleared;
if (eventHandler != null)
{
eventHandler(this, EventArgs.Empty);
}
}
private void OnItemPropertyChanged(object sender, PropertyChangedEventArgs args)
{
ItemPropertyChangedEventHandler eventHandler = this.ItemPropertyChanged;
if (eventHandler != null)
{
eventHandler(this, new ItemPropertyChangedEventArgs(sender, args.PropertyName));
}
}
}
Then you can subscribe to the ItemPropertyChanged event and do your stuff.

Removing Controls from asp.net page at runtime

I have an asp.net dashboard site that allows a user to load HTML templates from a dropdownlist. There are multiple types of DevExpress components on the page, including the ASPxDockPanel. If a user changes templates I get an error that the dockpanel already exists, I would like to include a recursive function like the one below that checks to see if any ASPxDockPanels are present on the page, and if they are present remove them. This works for only the first dock panel then bombs out. I think this is because an enumerable set of controls cannot be modified while looping through it. How can I loop though the controls and remove the dock panels at runtime?
protected void LoadTableTemplate(string selectedTemplate, int currentMode)
{
FindAllDockPanels(this);
}
public void FindAllDockPanels(Control ctrl)
{
if (ctrl != null)
{
foreach (Control control in ctrl.Controls)
{
if (control is ASPxDockPanel)
{
ctrl.Controls.Remove(control);
control.Dispose();
}
FindAllDockPanels(control);
}
}
}

Use a temporary collection, like so:
public void FindAllDockPanels(Control ctrl) {
if (ctrl != null) {
List<Control> remove = new List<Control>();
foreach (Control control in ctrl.Controls) {
if (control is ASPxDockPanel) {
remove.Add( control );
}
}
foreach(Control control in remove) {
control.Controls.Remove( control );
control.Dispose(); // do you really need to dispose of them?
}
FindAllDockPanels(control);
}
}
If you find yourself doing this often, it might be worth moving these "DelayedDelete" actions to an extension method, like so:
public static void DelayedRemove<T>(this IEnumerable<T item> collection, T itemToRemove) {
// add it to a private static dictionary bound to the `collection` instance.
}
public static void DelayedRemoveFinish(this IEnumerable<T item> collection) {
// empty the private static dictionary in here
}
then you'd use it like so:
public void FindAllDockPanels(Control ctrl) {
if (ctrl != null) {
foreach (Control control in ctrl.Controls) {
if (control is ASPxDockPanel) control.Controls.DelayedRemove( control );
}
control.Controls.DelayedRemoveFinish();
FindAllDockPanels(control);
}
}
Much cleaner, no? :)

DeferRefresh Error in C# [duplicate]

In wpf I setup a tab control that binds to a collection of objects each object has a data template with a data grid presenting the data. If I select a particular cell and put it into edit mode, leaving the grid by going to another tab this will cause the exception below to be thrown on returning the datagrid:
'DeferRefresh' is not allowed during an AddNew or EditItem transaction.
It appears that the cell never left edit mode. Is there an easy way to take the cell out of edit mode, or is something else going on here?
Update: It looks like if I do not bind the tab control to the data source, but instead explicitly define each tab and then bind each item in the data source to a content control this problem goes away. This is not really a great solution, so I would still like to know how to bind the collection directly to the tab control.
Update: So what I have actually done for my own solution is to use a ListView and a content control in place of a tab control. I use a style to make the list view look tab like. The view model exposes a set of child view models and allows the user to select one via the list view. The content control then presents the selected view model and each view model has an associated data template which contains the data grid. With this setup switching between view models while in edit mode on the grid will properly end edit mode and save the data.
Here is the xaml for setting this up:
<ListView ItemTemplate="{StaticResource MakeItemsLookLikeTabs}"
ItemsSource="{Binding ViewModels}"
SelectedItem="{Binding Selected}"
Style="{StaticResource MakeItLookLikeATabControl}"/>
<ContentControl Content="{Binding Selected}">
I'll accept Phil's answer as that should work also, but for me the solution above seems like it will be more portable between projects.

I implemented a behavior for the DataGrid based on code I found in this thread.
Usage:<DataGrid local:DataGridCommitEditBehavior.CommitOnLostFocus="True" />
Code:
using System.Collections.Generic;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Media;
/// <summary>
/// Provides an ugly hack to prevent a bug in the data grid.
/// https://connect.microsoft.com/VisualStudio/feedback/details/532494/wpf-datagrid-and-tabcontrol-deferrefresh-exception
/// </summary>
public class DataGridCommitEditBehavior
{
public static readonly DependencyProperty CommitOnLostFocusProperty =
DependencyProperty.RegisterAttached(
"CommitOnLostFocus",
typeof(bool),
typeof(DataGridCommitEditBehavior),
new UIPropertyMetadata(false, OnCommitOnLostFocusChanged));
/// <summary>
/// A hack to find the data grid in the event handler of the tab control.
/// </summary>
private static readonly Dictionary<TabPanel, DataGrid> ControlMap = new Dictionary<TabPanel, DataGrid>();
public static bool GetCommitOnLostFocus(DataGrid datagrid)
{
return (bool)datagrid.GetValue(CommitOnLostFocusProperty);
}
public static void SetCommitOnLostFocus(DataGrid datagrid, bool value)
{
datagrid.SetValue(CommitOnLostFocusProperty, value);
}
private static void CommitEdit(DataGrid dataGrid)
{
dataGrid.CommitEdit(DataGridEditingUnit.Cell, true);
dataGrid.CommitEdit(DataGridEditingUnit.Row, true);
}
private static DataGrid GetParentDatagrid(UIElement element)
{
UIElement childElement; // element from which to start the tree navigation, looking for a Datagrid parent
if (element is ComboBoxItem)
{
// Since ComboBoxItem.Parent is null, we must pass through ItemsPresenter in order to get the parent ComboBox
var parentItemsPresenter = VisualTreeFinder.FindParentControl<ItemsPresenter>(element as ComboBoxItem);
var combobox = parentItemsPresenter.TemplatedParent as ComboBox;
childElement = combobox;
}
else
{
childElement = element;
}
var parentDatagrid = VisualTreeFinder.FindParentControl<DataGrid>(childElement);
return parentDatagrid;
}
private static TabPanel GetTabPanel(TabControl tabControl)
{
return
(TabPanel)
tabControl.GetType().InvokeMember(
"ItemsHost",
BindingFlags.NonPublic | BindingFlags.GetProperty | BindingFlags.Instance,
null,
tabControl,
null);
}
private static void OnCommitOnLostFocusChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e)
{
var dataGrid = depObj as DataGrid;
if (dataGrid == null)
{
return;
}
if (e.NewValue is bool == false)
{
return;
}
var parentTabControl = VisualTreeFinder.FindParentControl<TabControl>(dataGrid);
var tabPanel = GetTabPanel(parentTabControl);
if (tabPanel != null)
{
ControlMap[tabPanel] = dataGrid;
}
if ((bool)e.NewValue)
{
// Attach event handlers
if (parentTabControl != null)
{
tabPanel.PreviewMouseLeftButtonDown += OnParentTabControlPreviewMouseLeftButtonDown;
}
dataGrid.LostKeyboardFocus += OnDataGridLostFocus;
dataGrid.DataContextChanged += OnDataGridDataContextChanged;
dataGrid.IsVisibleChanged += OnDataGridIsVisibleChanged;
}
else
{
// Detach event handlers
if (parentTabControl != null)
{
tabPanel.PreviewMouseLeftButtonDown -= OnParentTabControlPreviewMouseLeftButtonDown;
}
dataGrid.LostKeyboardFocus -= OnDataGridLostFocus;
dataGrid.DataContextChanged -= OnDataGridDataContextChanged;
dataGrid.IsVisibleChanged -= OnDataGridIsVisibleChanged;
}
}
private static void OnDataGridDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var dataGrid = (DataGrid)sender;
CommitEdit(dataGrid);
}
private static void OnDataGridIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var senderDatagrid = (DataGrid)sender;
if ((bool)e.NewValue == false)
{
CommitEdit(senderDatagrid);
}
}
private static void OnDataGridLostFocus(object sender, KeyboardFocusChangedEventArgs e)
{
var dataGrid = (DataGrid)sender;
var focusedElement = Keyboard.FocusedElement as UIElement;
if (focusedElement == null)
{
return;
}
var focusedDatagrid = GetParentDatagrid(focusedElement);
// Let's see if the new focused element is inside a datagrid
if (focusedDatagrid == dataGrid)
{
// If the new focused element is inside the same datagrid, then we don't need to do anything;
// this happens, for instance, when we enter in edit-mode: the DataGrid element loses keyboard-focus,
// which passes to the selected DataGridCell child
return;
}
CommitEdit(dataGrid);
}
private static void OnParentTabControlPreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
var dataGrid = ControlMap[(TabPanel)sender];
CommitEdit(dataGrid);
}
}
public static class VisualTreeFinder
{
/// <summary>
/// Find a specific parent object type in the visual tree
/// </summary>
public static T FindParentControl<T>(DependencyObject outerDepObj) where T : DependencyObject
{
var dObj = VisualTreeHelper.GetParent(outerDepObj);
if (dObj == null)
{
return null;
}
if (dObj is T)
{
return dObj as T;
}
while ((dObj = VisualTreeHelper.GetParent(dObj)) != null)
{
if (dObj is T)
{
return dObj as T;
}
}
return null;
}
}

I have managed to work around this issue by detecting when the user clicks on a TabItem and then committing edits on visible DataGrid in the TabControl. I'm assuming the user will expect their changes to still be there when they click back.
Code snippet:
// PreviewMouseDown event handler on the TabControl
private void TabControl_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
if (IsUnderTabHeader(e.OriginalSource as DependencyObject))
CommitTables(yourTabControl);
}
private bool IsUnderTabHeader(DependencyObject control)
{
if (control is TabItem)
return true;
DependencyObject parent = VisualTreeHelper.GetParent(control);
if (parent == null)
return false;
return IsUnderTabHeader(parent);
}
private void CommitTables(DependencyObject control)
{
if (control is DataGrid)
{
DataGrid grid = control as DataGrid;
grid.CommitEdit(DataGridEditingUnit.Row, true);
return;
}
int childrenCount = VisualTreeHelper.GetChildrenCount(control);
for (int childIndex = 0; childIndex < childrenCount; childIndex++)
CommitTables(VisualTreeHelper.GetChild(control, childIndex));
}
This is in the code behind.

This bug is solved in the .NET Framework 4.5. You can download it at this link.

What I think you should do is pretty close to what #myermian said.
There is an event called CellEditEnding end this event would allow you to intercept and make the decision to drop the unwanted row.
private void dataGrid1_CellEditEnding(object sender, DataGridCellEditEndingEventArgs e)
{
DataGrid grid = (DataGrid)sender;
TextBox cell = (TextBox)e.EditingElement;
if(String.IsNullOrEmpty(cell.Text) && e.EditAction == DataGridEditAction.Commit)
{
grid.CancelEdit(DataGridEditingUnit.Row);
e.Cancel = true;
}
}

autocompletebox focus in wpf

when I try to focus on my "autocompletetextbox" I failed I write autocompletetextbox.focus()
but the cursor still focus in another what should I do or write to enable to write in it or focus?

I experienced the same thing -- it does not work properly in its current form (I expect you're talking about the AutoCompleteBox that comes with the February 2010 release of WPFToolkit).
I created a subclass:
public class AutoCompleteFocusableBox : AutoCompleteBox
{
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
var textbox = Template.FindName("Text", this) as TextBox;
if(textbox != null) textbox.Focus();
}
}
This sets focus to the actual TextBox (called "Text") that is part of the default ControlTemplate.

You will have to override the Focus method to find the template of the Textbox.
public class FocusableAutoCompleteBox : AutoCompleteBox
{
public new void Focus()
{
var textbox = Template.FindName("Text", this) as TextBox;
if (textbox != null) textbox.Focus();
}
}

This is very old question, but I want to share my work-around.
Keyboard.Focus(autocompletetextbox);
autocompletetextbox.MoveFocus(new TraversalRequest(FocusNavigationDirection.Next));
This works in WPFToolkit v3.5.50211.1 on Visual Studio Express 2015 for Windows Desktop

It seems that you have to wait for the auto complete box to load first. Then set focus
<sdk:AutoCompleteBox
x:Name="_employeesAutoCompleteBox"
ItemsSource="{Binding Path=Employees}"
SelectedItem="{Binding SelectedEmployee, Mode=TwoWay}"
ValueMemberPath="DisplayName" >
</sdk:AutoCompleteBox>
_employeesAutoCompleteBox.Loaded +=
(sender, e) => ((AutoCompleteBox)sender).Focus();

This is my solution,
I found it easier than having inherited class
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
var textBox = FindVisualChild<TextBox>(CodedCommentBox);
textBox.Focus();
}
private TChildItem FindVisualChild<TChildItem>(DependencyObject obj) where TChildItem : DependencyObject
{
for (var i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
var child = VisualTreeHelper.GetChild(obj, i);
var item = child as TChildItem;
if (item != null)
{
return item;
}
var childOfChild = FindVisualChild<TChildItem>(child);
if (childOfChild != null)
{
return childOfChild;
}
}
return null;
}

This is my solution for setting focus on AutoCompleteTextBox control Text:
private void MyPageLoaded(object sender, RoutedEventArgs e)
{
var myPage = (MyControl)sender;
var autoTextBox = (AutoCompleteTextBox)myPage.FindName("AutoTextBox");
if (autoTextBox != null)
{
var innerTextBox = autoTextBox.textBox;
if (innerTextBox != null)
{
innerTextBox.Focus();
}
}
}

You could also use a extension method for this:
public static void ForceFocus(this AutoCompleteBox box)
{
if (box.Template.FindName("Text", box) is TextBox textbox)
{
textbox.Focus();
}
}

WPF treeview itemselected moves incorrectly when deleting an item

I have a treeview bound to an object tree. When I remove an object from the object tree, it is removed correctly from the tree view, but the treeview's default behaviour is to jump the selecteditem up to the deleted item's parent node. How can I change this so it jumps to the next item instead?
EDIT:
I updated my code with Aviad's suggestion. Here is my code..
public class ModifiedTreeView : TreeView
{
protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
{
base.OnItemsChanged(e);
if (e.Action == NotifyCollectionChangedAction.Remove)
{
if (e.OldStartingIndex - 1 > 0)
{
ModifiedTreeViewItem item =
this.ItemContainerGenerator.ContainerFromIndex(
e.OldStartingIndex - 2) as ModifiedTreeViewItem;
item.IsSelected = true;
}
}
}
protected override DependencyObject GetContainerForItemOverride()
{
return new ModifiedTreeViewItem();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is ModifiedTreeViewItem;
}
}
public class ModifiedTreeViewItem : TreeViewItem
{
protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
{
base.OnItemsChanged(e);
if (e.Action == NotifyCollectionChangedAction.Remove)
{
if (e.OldStartingIndex > 0)
{
ModifiedTreeViewItem item =
this.ItemContainerGenerator.ContainerFromIndex(
e.OldStartingIndex - 1) as ModifiedTreeViewItem;
item.IsSelected = true;
}
}
}
protected override DependencyObject GetContainerForItemOverride()
{
return new ModifiedTreeViewItem();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is ModifiedTreeViewItem;
}
}
The code above does not work unless I debug it, or in some way slow down the OnItemsChanged method. For example, if I put a thread.sleep(500) at the bottom of the OnItemsChanged method, it works, otherwise it does not. Any idea what I'm doing wrong? This is really strange.

The behavior you mention is controlled by a virtual method in the Selector class called OnItemsChanged (reference: Selector.OnItemsChanged Method) - In order to modify it, you should derive from TreeView and override that function. You might use reflector to base your implementation on the existing implementation, although it's pretty straightforward.
Here's the code for the treeview override TreeView.OnItemsChanged extracted using reflector:
protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
case NotifyCollectionChangedAction.Move:
break;
case NotifyCollectionChangedAction.Remove:
case NotifyCollectionChangedAction.Reset:
if ((this.SelectedItem == null) || this.IsSelectedContainerHookedUp)
{
break;
}
this.SelectFirstItem();
return;
case NotifyCollectionChangedAction.Replace:
{
object selectedItem = this.SelectedItem;
if ((selectedItem == null) || !selectedItem.Equals(e.OldItems[0]))
{
break;
}
this.ChangeSelection(selectedItem, this._selectedContainer, false);
return;
}
default:
throw new NotSupportedException(SR.Get("UnexpectedCollectionChangeAction", new object[] { e.Action }));
}
}
Alternatively, you might hook into the collection NotifyCollectionChanged event from one of your code-behind classes and explicitly change the current selection before the event reaches the TreeView (I'm not sure of this solution though because I am not sure of the order in which event delegates are called - the TreeView might get to process the event before you do - but it might work).

Original answer
In my original answer I guessed that you may be encountering a bug in WPF and gave a generic workaround for this kind of situation, which was to replace item.IsSelected = true; with:
Disptacher.BeginInvoke(DispatcherPriority.Input, new Action(() =>
{
item.IsSelected = true;
}));
I explained that the reason this kind of workaround does the trick 90% of the time is that it delays the selection until almost all current operations have finished processing.
When I actually tried the code you posted in your other question I discovered that it was indeed a bug in WPF but found a more direct and reliable workaround. I'll explain how I diagnosed the problem and then describe the workaround.
Diagnosis
I added a SelectedItemChanged handler with a breakpoint in it, and looked at the stack trace. This made it obvious where the problem lies. Here are selected portions of the stack trace:
...
System.Windows.Controls.TreeView.ChangeSelection
...
System.Windows.Controls.TreeViewItem.OnGotFocus
...
System.Windows.Input.FocusManager.SetFocusedElement
System.Windows.Input.KeyboardNavigation.UpdateFocusedElement
System.Windows.FrameworkElement.OnGotKeyboardFocus
System.Windows.Input.KeyboardFocusChangedEventArgs.InvokeEventHandler
...
System.Windows.Input.InputManager.ProcessStagingArea
System.Windows.Input.InputManager.ProcessInput
System.Windows.Input.KeyboardDevice.ChangeFocus
System.Windows.Input.KeyboardDevice.TryChangeFocus
System.Windows.Input.KeyboardDevice.Focus
System.Windows.Input.KeyboardDevice.ReevaluateFocusCallback
...
As you can see, KeyboardDevice has a ReevaluateFocusCallback private or internal method which changes the focus to the parent of the deleted TreeViewItem. This causes a GotFocus event which causes the parent item to be selected. This all happens in the background after your event handler returns.
Solution
Normally in this case I would tell you to just manually .Focus() the TreeViewItem you are selecting. That is difficult here because in a TreeView there is no easy way to get from an arbitrary data item to the corresponding container (there are separate ItemContainerGenerators at each level).
So I think your best solution is to force the focus to the parent node (just where you don't want it to end up), then set IsSelected in the child's data. That way the input manager will never decide it needs to move the focus on its own: It will find the focus already set to a valid IInputElement.
Here is some code to do that:
if(child != null)
{
SomeObject parent = child.Parent;
// Find the currently focused element in the TreeView's focus scope
DependencyObject focused =
FocusManager.GetFocusedElement(
FocusManager.GetFocusScope(tv)) as DependencyObject;
// Scan up the VisualTree to find the TreeViewItem for the parent
var parentContainer = (
from element in GetVisualAncestorsOfType<FrameworkElement>(focused)
where (element is TreeViewItem && element.DataContext == parent)
|| element is TreeView
select element
).FirstOrDefault();
parent.Children.Remove(child);
if(parent.Children.Count > 0)
{
// Before selecting child, first focus parent's container
if(parentContainer!=null) parentContainer.Focus();
parent.Children[0].IsSelected = true;
}
}
This also requires this helper method:
private IEnumerable<T> GetVisualAncestorsOfType<T>(DependencyObject obj) where T:DependencyObject
{
for(; obj!=null; obj = VisualTreeHelper.GetParent(obj))
if(obj is T)
yield return (T)obj;
}
This should be more reliable than using Dispatcher.BeginInvoke because it will work around this particular problem without making any assumptions about input queue ordering, Dispatcher priorities, and so forth.

This works for me (thanks to investigations provided above)
protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
base.OnItemsChanged(e);
if (e.Action == NotifyCollectionChangedAction.Remove)
{
Focus();
}
}

According to the answer provided by #Kirill I think the correct answer to this specific question would be the following code added to a class derived from TreeView.
protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Remove && SelectedItem != null)
{
var index = Items.IndexOf(SelectedItem);
if (index + 1 < Items.Count)
{
var item = Items.GetItemAt(index + 1) as TreeViewItem;
if (item != null)
{
item.IsSelected = true;
}
}
}
}

Based on the answers above, here's the solution that worked for me (it has fixed various other problems as well, such as the loss of focus after selecting an item via model etc.)
Note the OnSelected override (scroll all the way down) which actually did the trick.
This was compiled in VS2015 for Net 3.5.
using System.Windows;
using System.Windows.Controls;
using System.Collections.Specialized;
namespace WPF
{
public partial class TreeViewEx : TreeView
{
#region Overrides
protected override DependencyObject GetContainerForItemOverride()
{
return new TreeViewItemEx();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is TreeViewItemEx;
}
#endregion
}
public partial class TreeViewItemEx : TreeViewItem
{
#region Overrides
protected override DependencyObject GetContainerForItemOverride()
{
return new TreeViewItemEx();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is TreeViewItemEx;
}
protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Remove:
if (HasItems)
{
int newIndex = e.OldStartingIndex;
if (newIndex >= Items.Count)
newIndex = Items.Count - 1;
TreeViewItemEx item = ItemContainerGenerator.ContainerFromIndex(newIndex) as TreeViewItemEx;
item.IsSelected = true;
}
else
base.OnItemsChanged(e);
break;
default:
base.OnItemsChanged(e);
break;
}
}
protected override void OnSelected(RoutedEventArgs e)
{
base.OnSelected(e);
Focus();
}
#endregion
}
}