Why is the template binding not refreshing?

Question

I made this itemtemplate for a combobox:
<DataTemplate x:Key="EO_CategoryItemTemplate">
<Grid>
<Line
Stroke="Gray"
StrokeThickness="1"
VerticalAlignment="Center"
X1="0"
X2="{Binding ActualWidth, ElementName=cat1}"
Visibility="{Binding Active, Converter={StaticResource EO_BooleanToVisibility}, ConverterParameter=Reverse}"
/>
<TextBlock
x:Name="cat1"
Text="{Binding Name}"
ToolTipService.ToolTip="{Binding InactiveTooltip}"
VerticalAlignment="Center"
HorizontalAlignment="Left"
/>
</Grid>
</DataTemplate>
The problem is the line.  It seems to only get set in the combobox's main text ONCE.  On the first SelectedItem change.  After that, its length is still that of the first item.
In the popup listbox, it is fine.  Each item has a different length line.
Is there something I can do so that the combobox text has a line through the actual characters?

Answer 1

I spent some time looking at this and I'm afraid I have nothing but bad news.
My markup
<Grid x:Name="LayoutRoot" Background="White">
<Grid.Resources>
<DataTemplate x:Key="TestTemplate">
<Border HorizontalAlignment="Left">
<Grid VerticalAlignment="Center">
<TextBlock x:Name="NameTb"
Text="{Binding Name}" Foreground="Gray" />
<Line StrokeThickness="1"
VerticalAlignment="Center"
X1="1"
X2="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Border}}"
Stroke="Black" />
</Grid>
</Border>
</DataTemplate>
</Grid.Resources>
<ComboBox ItemsSource="{Binding Items}"
ItemTemplate="{StaticResource TestTemplate}" Height="30" Width="200" SelectionChanged="ComboBox_SelectionChanged"
/>
Code behind
private T FindControlByType<T>(DependencyObject container, string name) where T : DependencyObject
T foundControl = null;
//for each child object in the container
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(container); i++)
//is the object of the type we are looking for?
if (VisualTreeHelper.GetChild(container, i) is T && (VisualTreeHelper.GetChild(container, i).GetValue(FrameworkElement.NameProperty).Equals(name) || name == null))
foundControl = (T)VisualTreeHelper.GetChild(container, i);
break;
//if not, does it have children?
else if (VisualTreeHelper.GetChildrenCount(VisualTreeHelper.GetChild(container, i)) > 0)
//recursively look at its children
foundControl = FindControlByType<T>(VisualTreeHelper.GetChild(container, i), name);
if (foundControl != null)
break;
return foundControl;
private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
ComboBox cbo = sender as ComboBox;
if (cbo.SelectedItem != null)
int ix = cbo.Items.IndexOf(cbo.SelectedItem);
ComboBoxItem cboI = cbo.ItemContainerGenerator.ContainerFromIndex(ix) as ComboBoxItem;
Line ln = FindControlByType<Line>(cboI, null);
if (ln != null)
ln.Visibility = Visibility.Collapsed;
// ln.Visibility = Visibility.Visible;
// Debug.WriteLine(ln.X2.ToString());
//BindingExpression be = ln.GetBindingExpression(Line.X2Property);
//be.UpdateSource();
As you can see, I'm obtaining a reference to the line object.
When I  then:
explicitly updatesource on the binding, no effect.
debug writeline X2 - gives correct length, matching the item but not what you see in the selection.
I also tried invalidating and forcing arrange and measure and all that lark on the combo.
No joy.
This one is the weirdest.
If you set visibility to collapsed on the line you still see the "wrong" line visible in the selection part of the combo.
Despite the fact that the item in the combo has  no line.
Once that thing gets a line, it's keeping hold of it.
My conclusion is that this is a bug.
I would guess your chances of getting it fixed for Silverlight 4 are vanishingly slim though.
A work round I can think of, would be to maybe draw the text and image onto a bitmap.
Present those in the combo.
If your line visibility is actually dynamic that's not going to work.
Hope that helps.
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