WPF attached behavior triggering after button click - wpf

I have the following class / behavior which is being called on button click event. The issue is that it gets called after button_click event. How to call it before button click event?
The below mentioned style is defined in App.xaml for global usage
XAML:
<Style TargetType="Button">
<Setter Property="local:DefaultButtonBehaviour.DefaultButton" Value="True" />
</Style>
CODE:
public static class DefaultButtonBehaviour
{
/// 1. This is the boolean attached property with its getter and setter:
public static readonly DependencyProperty DefaultButtonProperty =
DependencyProperty.RegisterAttached
(
"DefaultButton",
typeof(bool),
typeof(DefaultButtonBehaviour),
new UIPropertyMetadata(false, OnDefaultButtonPropertyChanged)
);
public static bool GetDefaultButton(DependencyObject obj)
{
return (bool)obj.GetValue(DefaultButtonProperty);
}
private static void SetDefaultButton(DependencyObject obj, bool value)
{
obj.SetValue(DefaultButtonProperty, value);
}
/// 2. This is the change event of our attached property value:
/// * We get in the first parameter the dependency object to which the attached behavior was attached
/// * We get in the second parameter the value of the attached behavior.
/// * The implementation of the behavior is to check if we are attached to a textBox, and if so and the value of the behavior
/// is true, hook to the PreviewGotKeyboardFocus of the textbox.
private static void OnDefaultButtonPropertyChanged(DependencyObject dpo, DependencyPropertyChangedEventArgs args)
{
ButtonBase button = dpo as ButtonBase;
if (button != null)
{
if ((bool)args.NewValue)
{
button.Click += OnDefaultButtonClick;
}
else
{
button.Click -= OnDefaultButtonClick; ;
}
}
}
private static void OnDefaultButtonClick(object sender, RoutedEventArgs e)
{
ButtonBase btn = (ButtonBase)sender;
DependencyObject focusScope = FocusManager.GetFocusScope(btn);
FocusManager.SetFocusedElement(focusScope, btn);
Keyboard.Focus(btn);
}
}

If I am following the question properly, you could approach this by wiring up the Preview events. Hook into PreviewMouseDown and PreviewKeyDown (so you can handle the case where the user uses the return key to activate the button).

Related

How can I apply a custom sort for a WPF DataGrid from a style?

I have a style that I want to apply to a DataGrid. The DataGrid needs to run my custom sort code instead of the default DataGrid sort. The solution that I tried was as follows:
<Style TargetType="{x:Type DataGrid}" x:Key="FilteredDataGrid">
<EventSetter Event="Sorting" Handler="DataGrid_Sorting"/>
</Style>
And in the code-behind:
private void DataGrid_Sorting(object sender, DataGridSortingEventArgs e) {
e.Handled = true;
//Here is where I put the code for my custom sort.
}//DataGrid_Sorting
However, this code doesn't build. It seems to me that because the DataGrid.Sorting event is not a RoutedEvent, it can't be used in an EventSetter.
How can I customize the sorting for any DataGrid that has my style applied?
There is a workaround to provide a routed event when you only have a "normal" event:
Create an attached property that controls the event forwarding and an attached event that shall replace the original event. In order to do this, create a class DataGridEx (whatever class name you prefer) as a container for the attached property (DataGridEx.EnableSortingEvent) and event (DataGridEx.Sorting).
Also, create a custom RoutedEventArgs class that forwards the original sorting event args
public class DataGridExSortingEventArgs : RoutedEventArgs
{
public DataGridExSortingEventArgs(RoutedEvent routedEvent, DataGridSortingEventArgs sourceEventArgs) : base(routedEvent)
{
SourceEventArgs = sourceEventArgs;
}
public DataGridSortingEventArgs SourceEventArgs { get; set; }
}
public static class DataGridEx
{
public static bool GetEnableSortingEvent(DependencyObject obj)
{
return (bool)obj.GetValue(EnableSortingEventProperty);
}
public static void SetEnableSortingEvent(DependencyObject obj, bool value)
{
obj.SetValue(EnableSortingEventProperty, value);
}
// Setting this property to true enables the event forwarding from the DataGrid.Sorting event to the DataGridEx.Sorting RoutedEvent
public static readonly DependencyProperty EnableSortingEventProperty = DependencyProperty.RegisterAttached(
"EnableSortingEvent",
typeof(bool),
typeof(DataGridEx),
new FrameworkPropertyMetadata(false, new PropertyChangedCallback(OnEnableSortingChanged)));
private static void OnEnableSortingChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (d is DataGrid dg)
{
if ((bool)e.NewValue)
dg.Sorting += Dg_Sorting;
else
dg.Sorting -= Dg_Sorting;
}
}
// When DataGrid.Sorting is called and DataGridEx.EnableSortingEvent is true, raise the DataGridEx.Sorting event
private static void Dg_Sorting(object sender, DataGridSortingEventArgs e)
{
if (sender is DataGrid dg && GetEnableSortingEvent(dg))
{
dg.RaiseEvent(new DataGridExSortingEventArgs(SortingEvent, e));
}
}
// When DataGridEx.EnableSortingEvent is true, the DataGrid.Sorting event will be forwarded to this routed event
public static readonly RoutedEvent SortingEvent = EventManager.RegisterRoutedEvent(
"Sorting",
// only effective on the DataGrid itself
RoutingStrategy.Direct,
typeof(RoutedEventHandler),
typeof(DataGridEx));
public static void AddSortingHandler(DependencyObject d, RoutedEventHandler handler)
{
if (d is DataGrid dg)
dg.AddHandler(SortingEvent, handler);
}
public static void RemoveSortingHandler(DependencyObject d, RoutedEventHandler handler)
{
if (d is DataGrid dg)
dg.RemoveHandler(SortingEvent, handler);
}
}
Now use those in your style (with local being the xmlns for the namespace where DataGridEx is defined):
<Style TargetType="DataGrid">
<Setter Property="local:DataGridEx.EnableSortingEvent" Value="True"/>
<EventSetter Event="local:DataGridEx.Sorting" Handler="DataGrid_Sorting"/>
</Style>
The handler
private void DataGrid_Sorting(object sender, RoutedEventArgs e)
{
if (e is DataGridExSortingEventArgs args)
{
// will prevent datagrid default sorting
args.SourceEventArgs.Handled = true;
}
// More stuff
}
I hope this is what you needed. Had to refresh my memory about attached stuff :)

WPF TextBox referenced from presentationmodel gets unsync?

I have a textbox on my wpfgrid that I need to perform some tekst inserting and such on. To do this, the textbox is referenced into the presentationmodel from the view, ReferenceToTextBox (we do MVP with Prism). Also, the textbox in the view TextDescription is bound to the Description-property on the model.
We also have a dropdown-list containing some predefined text-blobs (adresses, VAT-numbers and such). When you choose one of these, they should be inserted into the textbox at the carets current position. Since you can't bind on CaretIndex, the above mentioned workaround is made. The dropdown-list is bound on SelectedItem to a property on the model, so when the SelectedItem changes, the property changes, and in the setter on the property a method is called to insert the text of the selected-item into the ReferenceToTextBox "virtual" textbox in the model (which should be just a reference to the textbox in the view).
However, if I delete all the text from the textbox in the view and add a new predefined text-blob. The ReferenceToTextBox.Text property still contains all the text that I deleted. It seems like the ReferenceToTextBox is no longer just a reference, but a whole own textbox. Which makes it even weirder when updates to ReferenceToTextBox.Text actually updates the "visual" textbox on the view.
What is actually happening here?
Not a direct answer to your question, but what about a derived TextBox class that actually allows binding to its CaretIndex property:
public class TextBoxEx : TextBox
{
public static readonly DependencyProperty CaretIndexProperty = DependencyProperty.Register(
"CaretIndex", typeof(int), typeof(TextBoxEx),
new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, CaretIndexChanged));
public new int CaretIndex
{
get { return (int)GetValue(CaretIndexProperty); }
set { SetValue(CaretIndexProperty, value); }
}
protected override void OnTextChanged(TextChangedEventArgs e)
{
base.OnTextChanged(e);
CaretIndex = base.CaretIndex;
}
protected override void OnKeyDown(KeyEventArgs e)
{
base.OnKeyDown(e);
CaretIndex = base.CaretIndex;
}
protected override void OnKeyUp(KeyEventArgs e)
{
base.OnKeyUp(e);
CaretIndex = base.CaretIndex;
}
protected override void OnMouseDown(MouseButtonEventArgs e)
{
base.OnMouseDown(e);
CaretIndex = base.CaretIndex;
}
protected override void OnMouseUp(MouseButtonEventArgs e)
{
base.OnMouseUp(e);
CaretIndex = base.CaretIndex;
}
private static void CaretIndexChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
if (obj is TextBox)
{
((TextBox)obj).CaretIndex = (int)e.NewValue;
}
}
}

How to disable dropdown button in WPF RibbonSplitButton control

I am using WPF Ribbon 4. I have a RibbonSplitButton control with dropdown menu of menu items.
When I set IsEnabled property of RibbonSplitButton to false only top button becomes disabled, not the button which opens dropdown menu.
Thanks in advance.
I solved this problem by creating my own split button, inheriting from RibbonSplitButton and adding an dependency property that I can bind to for enabling or disabling the split button alone.
public class MyRibbonSplitButton : RibbonSplitButton
{
public MyRibbonSplitButton()
: base()
{
}
/// <summary>
/// Gets or sets a value indicating whether the toggle button is enabled.
/// </summary>
/// <value><c>true</c> if the toggle button should be enabled; otherwise, <c>false</c>.</value>
public bool IsToggleButtonEnabled
{
get { return (bool)GetValue(IsToggleButtonEnabledProperty); }
set { SetValue(IsToggleButtonEnabledProperty, value); }
}
/// <summary>
/// Identifies the <see cref="IsToggleButtonEnabled"/> dependency property
/// </summary>
public static readonly DependencyProperty IsToggleButtonEnabledProperty =
DependencyProperty.Register(
"IsToggleButtonEnabled",
typeof(bool),
typeof(MyRibbonSplitButton),
new UIPropertyMetadata(true, new PropertyChangedCallback(MyRibbonSplitButton.ToggleButton_OnIsEnabledChanged)));
/// <summary>
/// Handles the PropertyChanged event for the IsToggleButtonEnabledProperty dependency property
/// </summary>
private static void ToggleButton_OnIsEnabledChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var button = sender as MyRibbonSplitButton;
var toggleButton = button.GetTemplateChild("PART_ToggleButton") as RibbonToggleButton;
toggleButton.IsEnabled = (bool)e.NewValue;
}
}
and in XAML:
<local:MyRibbonSplitButton Label="New" Command="{Binding SomeCommand}"
LargeImageSource="Images/Large/New.png"
ItemsSource="{Binding Templates}"
IsToggleButtonEnabled="{Binding HasTemplates}"/>
You can simply add a DropDownOpened="RibbonMenuButton_OnDropDownOpened" to the WPF and then
private void RibbonMenuButton_OnDropDownOpened(object sender, EventArgs e)
{
var rsb = sender as RibbonSplitButton;
if (rsb == null) return;
if (DataContext is GameCardViewModel vm)
{
rsb.IsDropDownOpen = vm.EasyInputMode;
}
}

Binding to ActualWidth does not work

In a Silverlight 3.0 application I'm attempting to create a rectangle in a canvas and have it stretch the whole width of the canvas. I have attempted to do this by binding to the ActualWidth property of a parent container (seem sample below), however while I don't see any binding errors the value is not being bound. The rectangle is not visible as its width is zero. In addition tried binding to the ActualWidth of the canvas that contains my rectangle but this made no difference.
I did find this bug logged on Microsoft Connect but there were no workarounds listed.
Has anyone been able to solve this issue or can they point to solution?
Edit: The original code sample was not accurate of what I'm trying to achieve, updated for more clarity.
<UserControl>
<Border BorderBrush="White"
BorderThickness="1"
CornerRadius="4"
HorizontalAlignment="Center">
<Grid x:Name="GridContainer">
<Rectangle Fill="Aqua"
Width="150"
Height="400" />
<Canvas>
<Rectangle Width="{Binding Path=ActualWidth, ElementName=GridContainer}"
Height="30"
Fill="Red" />
</Canvas>
<StackPanel>
<!-- other elements here -->
</StackPanel>
</Grid>
</Border>
</UserControl>
What are you trying to do that requires you to databind to the ActualWidth property?
This is a known issue with Silverlight, and there is no simple workaround.
One thing that could be done is to set up the visual tree in such a way that you do not need to actually set the Width of the Rectangle, and just allow it to stretch to the appropriate size. So in the example above, if you remove the Canvas (or change the Canvas to some other Panel) and leave the Rectangle's HorizontalAlignment set to Stretch, it will take up all of the available width (effectively the Width of the Grid).
However, this may not be possible in your particular case, and it may really be necessary to set up the databinding. It has already been established that this is not possible directly, but with the help of a proxy object, we can set up the required binding. Consider this code:
public class ActualSizePropertyProxy : FrameworkElement, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public FrameworkElement Element
{
get { return (FrameworkElement)GetValue(ElementProperty); }
set { SetValue(ElementProperty, value); }
}
public double ActualHeightValue
{
get{ return Element == null? 0: Element.ActualHeight; }
}
public double ActualWidthValue
{
get { return Element == null ? 0 : Element.ActualWidth; }
}
public static readonly DependencyProperty ElementProperty =
DependencyProperty.Register("Element", typeof(FrameworkElement), typeof(ActualSizePropertyProxy),
new PropertyMetadata(null,OnElementPropertyChanged));
private static void OnElementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((ActualSizePropertyProxy)d).OnElementChanged(e);
}
private void OnElementChanged(DependencyPropertyChangedEventArgs e)
{
FrameworkElement oldElement = (FrameworkElement)e.OldValue;
FrameworkElement newElement = (FrameworkElement)e.NewValue;
newElement.SizeChanged += new SizeChangedEventHandler(Element_SizeChanged);
if (oldElement != null)
{
oldElement.SizeChanged -= new SizeChangedEventHandler(Element_SizeChanged);
}
NotifyPropChange();
}
private void Element_SizeChanged(object sender, SizeChangedEventArgs e)
{
NotifyPropChange();
}
private void NotifyPropChange()
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("ActualWidthValue"));
PropertyChanged(this, new PropertyChangedEventArgs("ActualHeightValue"));
}
}
}
We can use this in xaml as follows:
<Grid x:Name="LayoutRoot">
<Grid.Resources>
<c:ActualSizePropertyProxy Element="{Binding ElementName=LayoutRoot}" x:Name="proxy" />
</Grid.Resources>
<TextBlock x:Name="tb1" Text="{Binding ActualWidthValue, ElementName=proxy}" />
</Grid>
So we are Binding TextBlock.Text to the ActualWidthValue on the proxy object. The proxy object in turn provides the ActualWidth of the Element, which is provided by another Binding.
This is not a simple solution to the problem, but it is the best that I can think of for how to databind to ActualWidth.
If you explained your scenario a bit more, it may be possible to come up with a simpler solution. DataBinding may not be required at all; would it be possible to just set the property from code in a SizeChanged event handler?
Using the mechanism of attached properties, properties which represent ActualHeight and ActualWidth and are updated by SizeChanged event can be defined. Its usage will look like the following.
<Grid local:SizeChange.IsEnabled="True" x:Name="grid1">...</Grid>
<TextBlock Text="{Binding ElementName=grid1,
Path=(local:SizeChange.ActualHeight)}"/>
Technical details can be found at the following:
http://darutk-oboegaki.blogspot.com/2011/07/binding-actualheight-and-actualwidth.html
The advantage of this solution compared to others is in that the attached properties defined in the solution (SizeChange.ActualHeight and SizeChange.ActualWidth) can be used for any FrameworkElement without creating any sub class. This solution is reusable and less invasive.
In the event that the link becomes stale, here is the SizeChange Class as shown on the link:
// Declare SizeChange class as a sub class of DependencyObject
// because we need to register attached properties.
public class SizeChange : DependencyObject
{
#region Attached property "IsEnabled"
// The name of IsEnabled property.
public const string IsEnabledPropertyName = "IsEnabled";
// Register an attached property named "IsEnabled".
// Note that OnIsEnabledChanged method is called when
// the value of IsEnabled property is changed.
public static readonly DependencyProperty IsEnabledProperty
= DependencyProperty.RegisterAttached(
IsEnabledPropertyName,
typeof(bool),
typeof(SizeChange),
new PropertyMetadata(false, OnIsEnabledChanged));
// Getter of IsEnabled property. The name of this method
// should not be changed because the dependency system
// uses it.
public static bool GetIsEnabled(DependencyObject obj)
{
return (bool)obj.GetValue(IsEnabledProperty);
}
// Setter of IsEnabled property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetIsEnabled(DependencyObject obj, bool value)
{
obj.SetValue(IsEnabledProperty, value);
}
#endregion
#region Attached property "ActualHeight"
// The name of ActualHeight property.
public const string ActualHeightPropertyName = "ActualHeight";
// Register an attached property named "ActualHeight".
// The value of this property is updated When SizeChanged
// event is raised.
public static readonly DependencyProperty ActualHeightProperty
= DependencyProperty.RegisterAttached(
ActualHeightPropertyName,
typeof(double),
typeof(SizeChange),
null);
// Getter of ActualHeight property. The name of this method
// should not be changed because the dependency system
// uses it.
public static double GetActualHeight(DependencyObject obj)
{
return (double)obj.GetValue(ActualHeightProperty);
}
// Setter of ActualHeight property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetActualHeight(DependencyObject obj, double value)
{
obj.SetValue(ActualHeightProperty, value);
}
#endregion
#region Attached property "ActualWidth"
// The name of ActualWidth property.
public const string ActualWidthPropertyName = "ActualWidth";
// Register an attached property named "ActualWidth".
// The value of this property is updated When SizeChanged
// event is raised.
public static readonly DependencyProperty ActualWidthProperty
= DependencyProperty.RegisterAttached(
ActualWidthPropertyName,
typeof(double),
typeof(SizeChange),
null);
// Getter of ActualWidth property. The name of this method
// should not be changed because the dependency system
// uses it.
public static double GetActualWidth(DependencyObject obj)
{
return (double)obj.GetValue(ActualWidthProperty);
}
// Setter of ActualWidth property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetActualWidth(DependencyObject obj, double value)
{
obj.SetValue(ActualWidthProperty, value);
}
#endregion
// This method is called when the value of IsEnabled property
// is changed. If the new value is true, an event handler is
// added to SizeChanged event of the target element.
private static void OnIsEnabledChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
// The given object must be a FrameworkElement instance,
// because we add an event handler to SizeChanged event
// of it.
var element = obj as FrameworkElement;
if (element == null)
{
// The given object is not an instance of FrameworkElement,
// meaning SizeChanged event is not available. So, nothing
// can be done for the object.
return;
}
// If IsEnabled=True
if (args.NewValue != null && (bool)args.NewValue == true)
{
// Attach to the element.
Attach(element);
}
else
{
// Detach from the element.
Detach(element);
}
}
private static void Attach(FrameworkElement element)
{
// Add an event handler to SizeChanged event of the element
// to take action when actual size of the element changes.
element.SizeChanged += HandleSizeChanged;
}
private static void Detach(FrameworkElement element)
{
// Remove the event handler from the element.
element.SizeChanged -= HandleSizeChanged;
}
// An event handler invoked when SizeChanged event is raised.
private static void HandleSizeChanged(object sender, SizeChangedEventArgs args)
{
var element = sender as FrameworkElement;
if (element == null)
{
return;
}
// Get the new actual height and width.
var width = args.NewSize.Width;
var height = args.NewSize.Height;
// Update values of SizeChange.ActualHeight and
// SizeChange.ActualWidth.
SetActualWidth(element, width);
SetActualHeight(element, height);
}
}
My solution is to declare my own DependencyProperty called RealWidth and update its value on the SizeChanged event. You can then bind to RealWidth, which will update, unlike the ActualWidth property.
public MyControl()
{
InitializeComponent();
SizeChanged += HandleSizeChanged;
}
public static DependencyProperty RealWidthProperty =
DependencyProperty.Register("RealWidth", typeof (double),
typeof (MyControl),
new PropertyMetadata(500D));
public double RealWidth
{
get { return (double) GetValue(RealWidthProperty); }
set { SetValue(RealWidthProperty, value); }
}
private void HandleSizeChanged(object sender, SizeChangedEventArgs e)
{
RealWidth = e.NewSize.Width;
}
Why not create a simple panel control that inherits from ContentPresenter and actually can provide the current size.
public class SizeNotifyPanel : ContentPresenter
{
public static DependencyProperty SizeProperty =
DependencyProperty.Register("Size",
typeof (Size),
typeof (SizeNotifyPanel),
null);
public Size Size
{
get { return (Size) GetValue(SizeProperty); }
set { SetValue(SizeProperty, value); }
}
public SizeNotifyPanel()
{
SizeChanged += (s, e) => Size = e.NewSize;
}
}
It should then be used as wrapper for the actual content.
<local:SizeNotifyPanel x:Name="Content">
<TextBlock Text="{Binding Size.Height, ElementName=Content}" />
</local:SizeNotifyPanel>
Worked for me like a charm and looks clean.
Based on #darutk's answer, here's an attached property-based solution which does the job very elegantly.
public static class SizeBindings
{
public static readonly DependencyProperty ActualHeightProperty =
DependencyProperty.RegisterAttached("ActualHeight", typeof (double), typeof (SizeBindings),
new PropertyMetadata(0.0));
public static readonly DependencyProperty ActualWidthProperty =
DependencyProperty.RegisterAttached("ActualWidth", typeof (Double), typeof (SizeBindings),
new PropertyMetadata(0.0));
public static readonly DependencyProperty IsEnabledProperty =
DependencyProperty.RegisterAttached("IsEnabled", typeof (bool), typeof (SizeBindings),
new PropertyMetadata(false, HandlePropertyChanged));
private static void HandlePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var element = d as FrameworkElement;
if (element == null)
{
return;
}
if ((bool) e.NewValue == false)
{
element.SizeChanged -= HandleSizeChanged;
}
else
{
element.SizeChanged += HandleSizeChanged;
}
}
private static void HandleSizeChanged(object sender, SizeChangedEventArgs e)
{
var element = sender as FrameworkElement;
SetActualHeight(element, e.NewSize.Height);
SetActualWidth(element, e.NewSize.Width);
}
public static bool GetIsEnabled(DependencyObject obj)
{
return (bool)obj.GetValue(IsEnabledProperty);
}
public static void SetIsEnabled(DependencyObject obj, bool value)
{
obj.SetValue(IsEnabledProperty, value);
}
public static Double GetActualWidth(DependencyObject obj)
{
return (Double) obj.GetValue(ActualWidthProperty);
}
public static void SetActualWidth(DependencyObject obj, Double value)
{
obj.SetValue(ActualWidthProperty, value);
}
public static double GetActualHeight(DependencyObject obj)
{
return (double)obj.GetValue(ActualHeightProperty);
}
public static void SetActualHeight(DependencyObject obj, double value)
{
obj.SetValue(ActualHeightProperty, value);
}
}
Use it like this:
<Grid>
<Border x:Name="Border" behaviors:SizeBindings.IsEnabled="True"/>
<Border MinWidth="{Binding (behaviors:SizeBindings.ActualWidth), ElementName=Border}"/>
</Grid>
I've tested the updated xaml that you publishing using a TestConverter to see what value gets passed to the width and it is working for me (I am using VS 2010 B2). To use the TestConverter just set a breakpoint in the Convert method.
public class TestConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
}
A value of 150 was passed in and the Rectangle had a width of 150.
Were you expecting something different?
This is an as an aside answer which may help someone for binding to the ActualWidth.
My process didn't need a change event, it needed an end result of a value in its current state. So I created a dependency property called Target on my custom control/process as a FrameworkElement and the consumer xaml would bind to the actual object in question.
When it was time for the calculation the code could pulled the actual object and extracted it's ActualWidth from it.
Dependency Property on Control
public FrameworkElement Target
{
get { return (FrameworkElement)GetValue(TargetProperty);}
set { SetValue(TargetProperty, value);}
}
// Using a DependencyProperty as the backing store for Target.
// This enables animation, styling, binding, general access etc...
public static readonly DependencyProperty TargetProperty =
DependencyProperty.Register("Target", typeof(FrameworkElement),
typeof(ThicknessWrapper),
new PropertyMetadata(null, OnTargetChanged));
XAML on Consumer side showing a binding to a Rectangle
<local:ThicknessWrapper Target="{Binding ElementName=thePanel}"/>
<Rectangle x:Name="thePanel" HorizontalAlignment="Stretch" Height="20" Fill="Blue"/>
Code to Acquire
double width;
if (Target != null)
width = Target.ActualWidth; // Gets the current value.
Based on KeithMahoney's answer, it works fine on my UWP App and solves my problem. However, I cannot see my control in Design time because both the initial values of ActualWidthValue and ActualHeightValue are not provided in Design time. Although it works fine in running time, it is inconvenient for designing the layout of my control. With a little modification, this problem can be solved.
In his c# code for both properties ActualWidthValue and ActualHeightValue, add
set {;}
to let us can provide dummy values from XAML code. Although it is no use for running time, it can be used for design time.
In the declaration of Resources of his XAML code, provide c:ActualSizePropertyProxy suitable values for ActualWidthValue and ActualHeightValue such as
ActualHeightValue="800" ActualWidthValue="400"
Then it will show you a 400x800 control in design time.

How can I cancel a user's WPF TreeView click?

I've got a WPF application with a Treeview control.
When the user clicks a node on the tree, other TextBox, ComboBox, etc. controls on the page are populated with appropriate values.
The user can then make changes to those values and save his or her changes by clicking a Save button.
However, if the user selects a different Treeview node without saving his or her changes, I want to display a warning and an opportunity to cancel that selection.
MessageBox: Continue and discard your unsaved changes? OK/Cancel http://img522.imageshack.us/img522/2897/discardsj3.gif
XAML...
<TreeView Name="TreeViewThings"
...
TreeViewItem.Unselected="TreeViewThings_Unselected"
TreeViewItem.Selected="TreeViewThings_Selected" >
Visual Basic...
Sub TreeViewThings_Unselected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim OldThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
If CancelDueToUnsavedChanges(OldThing) Then
'put canceling code here
End If
End Sub
Sub TreeViewThings_Selected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim NewThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
PopulateControlsFromThing(NewThing)
End Sub
How can I cancel those unselect/select events?
Update: I've asked a follow-up question...
How do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
UPDATE
Realized I could put the logic in SelectedItemChanged instead. A little cleaner solution.
Xaml
<TreeView Name="c_treeView"
SelectedItemChanged="c_treeView_SelectedItemChanged">
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsSelected" Value="{Binding Path=IsSelected, Mode=TwoWay}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
Code behind. I have some classes that is my ItemsSource of the TreeView so I made an interface (MyInterface) that exposes the IsSelected property for all of them.
private MyInterface m_selectedTreeViewItem = null;
private void c_treeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (m_selectedTreeViewItem != null)
{
if (e.NewValue == m_selectedTreeViewItem)
{
// Will only end up here when reversing item
// Without this line childs can't be selected
// twice if "No" was pressed in the question..
c_treeView.Focus();
}
else
{
if (MessageBox.Show("Change TreeViewItem?",
"Really change",
MessageBoxButton.YesNo,
MessageBoxImage.Question) != MessageBoxResult.Yes)
{
EventHandler eventHandler = null;
eventHandler = new EventHandler(delegate
{
c_treeView.LayoutUpdated -= eventHandler;
m_selectedTreeViewItem.IsSelected = true;
});
// Will be fired after SelectedItemChanged, to early to change back here
c_treeView.LayoutUpdated += eventHandler;
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
I haven't found any situation where it doesn't revert back to the previous item upon pressing "No".
I had to solve the same problem, but in multiple treeviews in my application. I derived TreeView and added event handlers, partly using Meleak's solution and partly using the extension methods from this forum: http://forums.silverlight.net/t/65277.aspx/1/10
I thought I'd share my solution with you, so here is my complete reusable TreeView that handles "cancel node change":
public class MyTreeView : TreeView
{
public static RoutedEvent PreviewSelectedItemChangedEvent;
public static RoutedEvent SelectionCancelledEvent;
static MyTreeView()
{
PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent("PreviewSelectedItemChanged", RoutingStrategy.Bubble,
typeof(RoutedPropertyChangedEventHandler<object>), typeof(MyTreeView));
SelectionCancelledEvent = EventManager.RegisterRoutedEvent("SelectionCancelled", RoutingStrategy.Bubble,
typeof(RoutedEventHandler), typeof(MyTreeView));
}
public event RoutedPropertyChangedEventHandler<object> PreviewSelectedItemChanged
{
add { AddHandler(PreviewSelectedItemChangedEvent, value); }
remove { RemoveHandler(PreviewSelectedItemChangedEvent, value); }
}
public event RoutedEventHandler SelectionCancelled
{
add { AddHandler(SelectionCancelledEvent, value); }
remove { RemoveHandler(SelectionCancelledEvent, value); }
}
private object selectedItem = null;
protected override void OnSelectedItemChanged(RoutedPropertyChangedEventArgs<object> e)
{
if (e.NewValue == selectedItem)
{
this.Focus();
var args = new RoutedEventArgs(SelectionCancelledEvent);
RaiseEvent(args);
}
else
{
var args = new RoutedPropertyChangedEventArgs<object>(e.OldValue, e.NewValue, PreviewSelectedItemChangedEvent);
RaiseEvent(args);
if (args.Handled)
{
EventHandler eventHandler = null;
eventHandler = delegate
{
this.LayoutUpdated -= eventHandler;
var treeViewItem = this.ContainerFromItem(selectedItem);
if (treeViewItem != null)
treeViewItem.IsSelected = true;
};
this.LayoutUpdated += eventHandler;
}
else
{
selectedItem = this.SelectedItem;
base.OnSelectedItemChanged(e);
}
}
}
}
public static class TreeViewExtensions
{
public static TreeViewItem ContainerFromItem(this TreeView treeView, object item)
{
if (item == null) return null;
var containerThatMightContainItem = (TreeViewItem)treeView.ItemContainerGenerator.ContainerFromItem(item);
return containerThatMightContainItem ?? ContainerFromItem(treeView.ItemContainerGenerator, treeView.Items, item);
}
private static TreeViewItem ContainerFromItem(ItemContainerGenerator parentItemContainerGenerator, ItemCollection itemCollection, object item)
{
foreach (var child in itemCollection)
{
var parentContainer = (TreeViewItem)parentItemContainerGenerator.ContainerFromItem(child);
var containerThatMightContainItem = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(item);
if (containerThatMightContainItem != null)
return containerThatMightContainItem;
var recursionResult = ContainerFromItem(parentContainer.ItemContainerGenerator, parentContainer.Items, item);
if (recursionResult != null)
return recursionResult;
}
return null;
}
}
Here is an example of usage (codebehind for window containing a MyTreeView):
private void theTreeView_PreviewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (e.OldValue != null)
e.Handled = true;
}
private void theTreeView_SelectionCancelled(object sender, RoutedEventArgs e)
{
MessageBox.Show("Cancelled");
}
After choosing the first node in the treeview, all other node changes are cancelled and a message box is displayed.
You can't actually put your logic into the OnSelectedItemChanged Method, if the logic is there the Selected Item has actually already changed.
As suggested by another poster, the PreviewMouseDown handler is a better spot to implement the logic, however, a fair amount of leg work still needs to be done.
Below is my 2 cents:
First the TreeView that I have implemented:
public class MyTreeView : TreeView
{
static MyTreeView( )
{
DefaultStyleKeyProperty.OverrideMetadata(
typeof(MyTreeView),
new FrameworkPropertyMetadata(typeof(TreeView)));
}
// Register a routed event, note this event uses RoutingStrategy.Tunnel. per msdn docs
// all "Preview" events should use tunneling.
// http://msdn.microsoft.com/en-us/library/system.windows.routedevent.routingstrategy.aspx
public static RoutedEvent PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent(
"PreviewSelectedItemChanged",
RoutingStrategy.Tunnel,
typeof(CancelEventHandler),
typeof(MyTreeView));
// give CLR access to routed event
public event CancelEventHandler PreviewSelectedItemChanged
{
add
{
AddHandler(PreviewSelectedItemChangedEvent, value);
}
remove
{
RemoveHandler(PreviewSelectedItemChangedEvent, value);
}
}
// override PreviewMouseDown
protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
{
// determine which item is going to be selected based on the current mouse position
object itemToBeSelected = this.GetObjectAtPoint<TreeViewItem>(e.GetPosition(this));
// selection doesn't change if the target point is null (beyond the end of the list)
// or if the item to be selected is already selected.
if (itemToBeSelected != null && itemToBeSelected != SelectedItem)
{
bool shouldCancel;
// call our new event
OnPreviewSelectedItemChanged(out shouldCancel);
if (shouldCancel)
{
// if we are canceling the selection, mark this event has handled and don't
// propogate the event.
e.Handled = true;
return;
}
}
// otherwise we want to continue normally
base.OnPreviewMouseDown(e);
}
protected virtual void OnPreviewSelectedItemChanged(out bool shouldCancel)
{
CancelEventArgs e = new CancelEventArgs( );
if (PreviewSelectedItemChangedEvent != null)
{
// Raise our event with our custom CancelRoutedEventArgs
RaiseEvent(new CancelRoutedEventArgs(PreviewSelectedItemChangedEvent, e));
}
shouldCancel = e.Cancel;
}
}
some extension methods to support the TreeView finding the object under the mouse.
public static class ItemContainerExtensions
{
// get the object that exists in the container at the specified point.
public static object GetObjectAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
// ItemContainer - can be ListViewItem, or TreeViewItem and so on(depends on control)
ItemContainer obj = GetContainerAtPoint<ItemContainer>(control, p);
if (obj == null)
return null;
// it is worth noting that the passed _control_ may not be the direct parent of the
// container that exists at this point. This can be the case in a TreeView, where the
// parent of a TreeViewItem may be either the TreeView or a intermediate TreeViewItem
ItemsControl parentGenerator = obj.GetParentItemsControl( );
// hopefully this isn't possible?
if (parentGenerator == null)
return null;
return parentGenerator.ItemContainerGenerator.ItemFromContainer(obj);
}
// use the VisualTreeHelper to find the container at the specified point.
public static ItemContainer GetContainerAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
HitTestResult result = VisualTreeHelper.HitTest(control, p);
DependencyObject obj = result.VisualHit;
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemContainer))
{
obj = VisualTreeHelper.GetParent(obj);
}
// Will return null if not found
return obj as ItemContainer;
}
// walk up the visual tree looking for the nearest ItemsControl parent of the specified
// depObject, returns null if one isn't found.
public static ItemsControl GetParentItemsControl(this DependencyObject depObject)
{
DependencyObject obj = VisualTreeHelper.GetParent(depObject);
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemsControl))
{
obj = VisualTreeHelper.GetParent(obj);
}
// will return null if not found
return obj as ItemsControl;
}
}
and last, but not least the custom EventArgs that leverage the RoutedEvent subsystem.
public class CancelRoutedEventArgs : RoutedEventArgs
{
private readonly CancelEventArgs _CancelArgs;
public CancelRoutedEventArgs(RoutedEvent #event, CancelEventArgs cancelArgs)
: base(#event)
{
_CancelArgs = cancelArgs;
}
// override the InvokeEventHandler because we are going to pass it CancelEventArgs
// not the normal RoutedEventArgs
protected override void InvokeEventHandler(Delegate genericHandler, object genericTarget)
{
CancelEventHandler handler = (CancelEventHandler)genericHandler;
handler(genericTarget, _CancelArgs);
}
// the result
public bool Cancel
{
get
{
return _CancelArgs.Cancel;
}
}
}
Instead of selecting for Selected/Unselected, a better route might be to hook into PreviewMouseDown. The preblem with handling a Selected and Unselected event is that the event has already occurred when you receive the notification. There is nothing to cancel because it's already happened.
On the other hand, Preview events are cancelable. It's not the exact event you want but it does give you the oppuritunity to prevent the user from selecting a different node.
You can't cancel the event like you can, for example, a Closing event. But you can undo it if you cache the last selected value. The secret is you have to change the selection without re-firing the SelectionChanged event. Here's an example:
private object _LastSelection = null;
private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (IsUpdated)
{
MessageBoxResult result = MessageBox.Show("The current record has been modified. Are you sure you want to navigate away? Click Cancel to continue editing. If you click OK all changes will be lost.", "Warning", MessageBoxButton.OKCancel, MessageBoxImage.Hand);
switch (result)
{
case MessageBoxResult.Cancel:
e.Handled = true;
// disable event so this doesn't go into an infinite loop when the selection is changed to the cached value
PersonListView.SelectionChanged -= new SelectionChangedEventHandler(OnSelectionChanged);
PersonListView.SelectedItem = _LastSelection;
PersonListView.SelectionChanged += new SelectionChangedEventHandler(OnSelectionChanged);
return;
case MessageBoxResult.OK:
// revert the object to the original state
LocalDataContext.Persons.GetOriginalEntityState(_LastSelection).CopyTo(_LastSelection);
IsUpdated = false;
Refresh();
break;
default:
throw new ApplicationException("Invalid response.");
}
}
// cache the selected item for undo
_LastSelection = PersonListView.SelectedItem;
}
CAMS_ARIES:
XAML:
code :
private bool ManejarSeleccionNodoArbol(Object origen)
{
return true; // with true, the selected nodo don't change
return false // with false, the selected nodo change
}
private void Arbol_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled = ManejarSeleccionNodoArbol(e.Source);
}
}
private void Arbol_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled=ManejarSeleccionNodoArbol(e.Source);
}
}
Since the SelectedItemChanged event is triggered after the SelectedItem has already changed, you can't really cancel the event at this point.
What you can do is listen for mouse-clicks and cancel them before the SelectedItem gets changed.
You could create your custom control that derives from TreeView and then override the OnSelectedItemChanged method.
Before calling the base, you could first fire a custom event with a CancelEventArgs parameter. If the parameter.Cancel become true, then don't call the base, but select the old item instead (be careful that the OnSelectedItemChanged will be called again).
Not the best solution, but at least this keeps the logic inside the tree control, and there is not chance that the selection change event fires more than it's needed. Also, you don't need to care if the user clicked the tree, used the keyboard or maybe the selection changed programatically.
I solved this problem for 1 tree view and display of 1 document at a time. This solution is based on an attachable behavior that can be attached to a normal treeview:
<TreeView Grid.Column="0"
ItemsSource="{Binding TreeViewItems}"
behav:TreeViewSelectionChangedBehavior.ChangedCommand="{Binding SelectItemChangedCommand}"
>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}"
ToolTipService.ShowOnDisabled="True"
VerticalAlignment="Center" Margin="3" />
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
and the code for the behavior is this:
/// <summary>
/// Source:
/// http://stackoverflow.com/questions/1034374/drag-and-drop-in-mvvm-with-scatterview
/// http://social.msdn.microsoft.com/Forums/de-DE/wpf/thread/21bed380-c485-44fb-8741-f9245524d0ae
///
/// Attached behaviour to implement the SelectionChanged command/event via delegate command binding or routed commands.
/// </summary>
public static class TreeViewSelectionChangedBehavior
{
#region fields
/// <summary>
/// Field of attached ICommand property
/// </summary>
private static readonly DependencyProperty ChangedCommandProperty = DependencyProperty.RegisterAttached(
"ChangedCommand",
typeof(ICommand),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(null, OnSelectionChangedCommandChange));
/// <summary>
/// Implement backing store for UndoSelection dependency proeprty to indicate whether selection should be
/// cancelled via MessageBox query or not.
/// </summary>
public static readonly DependencyProperty UndoSelectionProperty =
DependencyProperty.RegisterAttached("UndoSelection",
typeof(bool),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(false, OnUndoSelectionChanged));
#endregion fields
#region methods
#region ICommand changed methods
/// <summary>
/// Setter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <param name="value"></param>
public static void SetChangedCommand(DependencyObject source, ICommand value)
{
source.SetValue(ChangedCommandProperty, value);
}
/// <summary>
/// Getter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <returns></returns>
public static ICommand GetChangedCommand(DependencyObject source)
{
return (ICommand)source.GetValue(ChangedCommandProperty);
}
#endregion ICommand changed methods
#region UndoSelection methods
public static bool GetUndoSelection(DependencyObject obj)
{
return (bool)obj.GetValue(UndoSelectionProperty);
}
public static void SetUndoSelection(DependencyObject obj, bool value)
{
obj.SetValue(UndoSelectionProperty, value);
}
#endregion UndoSelection methods
/// <summary>
/// This method is hooked in the definition of the <seealso cref="ChangedCommandProperty"/>.
/// It is called whenever the attached property changes - in our case the event of binding
/// and unbinding the property to a sink is what we are looking for.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnSelectionChangedCommandChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.SelectedItemChanged -= Selection_Changed;
var command = e.NewValue as ICommand;
if (command != null)
{
// the property is attached so we attach the Drop event handler
uiElement.SelectedItemChanged += Selection_Changed;
}
}
}
/// <summary>
/// This method is called when the selection changed event occurs. The sender should be the control
/// on which this behaviour is attached - so we convert the sender into a <seealso cref="UIElement"/>
/// and receive the Command through the <seealso cref="GetChangedCommand"/> getter listed above.
///
/// The <paramref name="e"/> parameter contains the standard EventArgs data,
/// which is unpacked and reales upon the bound command.
///
/// This implementation supports binding of delegate commands and routed commands.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void Selection_Changed(object sender, RoutedPropertyChangedEventArgs<object> e)
{
var uiElement = sender as TreeView;
// Sanity check just in case this was somehow send by something else
if (uiElement == null)
return;
ICommand changedCommand = TreeViewSelectionChangedBehavior.GetChangedCommand(uiElement);
// There may not be a command bound to this after all
if (changedCommand == null)
return;
// Check whether this attached behaviour is bound to a RoutedCommand
if (changedCommand is RoutedCommand)
{
// Execute the routed command
(changedCommand as RoutedCommand).Execute(e.NewValue, uiElement);
}
else
{
// Execute the Command as bound delegate
changedCommand.Execute(e.NewValue);
}
}
/// <summary>
/// Executes when the bound boolean property indicates that a user should be asked
/// about changing a treeviewitem selection instead of just performing it.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnUndoSelectionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.PreviewMouseDown -= uiElement_PreviewMouseDown;
var command = (bool)e.NewValue;
if (command == true)
{
// the property is attached so we attach the Drop event handler
uiElement.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
}
/// <summary>
/// Based on the solution proposed here:
/// Source: http://stackoverflow.com/questions/20244916/wpf-treeview-selection-change
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void uiElement_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
// first did the user click on a tree node?
var source = e.OriginalSource as DependencyObject;
while (source != null && !(source is TreeViewItem))
source = VisualTreeHelper.GetParent(source);
var itemSource = source as TreeViewItem;
if (itemSource == null)
return;
var treeView = sender as TreeView;
if (treeView == null)
return;
bool undoSelection = TreeViewSelectionChangedBehavior.GetUndoSelection(treeView);
if (undoSelection == false)
return;
// Cancel the attempt to select an item.
var result = MessageBox.Show("The current document has unsaved data. Do you want to continue without saving data?", "Are you really sure?",
MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No);
if (result == MessageBoxResult.No)
{
// Cancel the attempt to select a differnet item.
e.Handled = true;
}
else
{
// Lets disable this for a moment, otherwise, we'll get into an event "recursion"
treeView.PreviewMouseDown -= uiElement_PreviewMouseDown;
// Select the new item - make sure a SelectedItemChanged event is fired in any case
// Even if this means that we have to deselect/select the one and the same item
if (itemSource.IsSelected == true )
itemSource.IsSelected = false;
itemSource.IsSelected = true;
// Lets enable this to get back to business for next selection
treeView.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
#endregion methods
}
In this example I am showing a blocking message box in order to block the PreviewMouseDown event when it occurs. The event is then handled to signal that selection is cancelled or it is not handled to let the treeview itself handle the event by selecting the item that is about to be selected.
The behavior then invokes a bound command in the viewmodel if the user decides to continue anyway (PreviewMouseDown event is not handled by attached behavior and bound command is invoked.
I guess the message box showing could be done in other ways but I think its essential here to block the event when it happens since its otherwise not possible to cancel it(?). So, the only improve I could possible think off about this code is to bind some strings to make the displayed message configurable.
I have written an article that contains a downloadable sample since this is otherwise a difficult area to explain (one has to make many assumptions about missing parts that and the may not always be shared by all readers)
Here is an article that contains my results:
http://www.codeproject.com/Articles/995629/Cancelable-TreeView-Navigation-for-Documents-in-WP
Please comment on this solution and let me know if you see room for improvement.

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