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C# WPF The global style not working in some parts of the code [duplicate]

I am trying to learn something about WPF and I am quite amazed by its flexibility.
However, I have hit a problem with Styles and DataTemplates, which is little bit confusing.
I have defined below test page to play around a bit with styles etc and found that the Styles defined in <Page.Resources> for Border and TextBlock are not applied in the DataTemplate, but Style for ProgressBar defined in exactly the same way is applied.
Source code (I just use Kaxaml and XamlPadX to view the result)
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Page.Resources>
<Style TargetType="{x:Type Border}">
<Setter Property="Background" Value="SkyBlue"/>
<Setter Property="BorderBrush" Value="Black"/>
<Setter Property="BorderThickness" Value="2"/>
<Setter Property="CornerRadius" Value="5"/>
</Style>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="FontWeight" Value="Bold"/>
</Style>
<Style TargetType="{x:Type ProgressBar}">
<Setter Property="Height" Value="10"/>
<Setter Property="Width" Value="100"/>
<Setter Property="Foreground" Value="Red"/>
</Style>
<XmlDataProvider x:Key="TestData" XPath="/TestData">
<x:XData>
<TestData xmlns="">
<TestElement>
<Name>Item 1</Name>
<Value>25</Value>
</TestElement>
<TestElement>
<Name>Item 2</Name>
<Value>50</Value>
</TestElement>
</TestData>
</x:XData>
</XmlDataProvider>
<HierarchicalDataTemplate DataType="TestElement">
<Border Height="45" Width="120" Margin="5,5">
<StackPanel Orientation="Vertical" Margin="5,5" VerticalAlignment="Center" HorizontalAlignment="Center">
<TextBlock HorizontalAlignment="Center" Text="{Binding XPath=Name}"/>
<ProgressBar Value="{Binding XPath=Value}"/>
</StackPanel>
</Border>
</HierarchicalDataTemplate>
</Page.Resources>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
<StackPanel Orientation="Vertical" VerticalAlignment="Center">
<Border Height="45" Width="120" Margin="5,5">
<StackPanel Orientation="Vertical" VerticalAlignment="Center" HorizontalAlignment="Center">
<TextBlock HorizontalAlignment="Center" Text="Item 1"/>
<ProgressBar Value="25"/>
</StackPanel>
</Border>
<Border Height="45" Width="120" Margin="5,5">
<StackPanel Orientation="Vertical" VerticalAlignment="Center" HorizontalAlignment="Center">
<TextBlock HorizontalAlignment="Center" Text="Item 2"/>
<ProgressBar Value="50"/>
</StackPanel>
</Border>
</StackPanel>
<ListBox Margin="10,10" Width="140" ItemsSource="{Binding Source={StaticResource TestData}, XPath=TestElement}"/>
</StackPanel>
</Page>
I suspect it has something to do with default styles etc, but more puzzling is why some Styles are applied and some not. I cannot find an easy explanation for above anywhere and thus would like to ask if someone would be kind enough to explain this behaviour in lamens' terms with possible links to technical description, i.e. to MSDN or so.
Thanks in advance for you support!

I discovered a simple workaround for this. For any elements that are not able to search outside the data template encapsulation boundary (i.e. are not being implicitly styled), you can just declare an empty style within the data template for that element type and use the BasedOn attribute of the style to find the correct implicit style outside the data template to apply.
In the example below, the TextBox is able to search outside the data template encapsulation boundary (because it inherits from Control?), but the TextBlock is not able to, so I declare the empty style for it which can search outside the data template.
<ItemsControl.ItemTemplate>
<DataTemplate>
<DataTemplate.Resources>
<Style TargetType="TextBlock" BasedOn="{StaticResource {x:Type TextBlock}}" />
</DataTemplate.Resources>
<DockPanel>
<TextBlock Text="{Binding Name}" />
<TextBox Text="{Binding Value}" />
</DockPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>

This is actually by design. Elements that do not derive from Control will not pick up implicit Styles, unless they are in the application resources.
This link explains this in more detail, or you can view the Connent bug report.

I've looked into this also, and I personally think it's a bug. I've noticed that the style is set if you name your styles like so:
<Style x:Key="BorderStyle" TargetType="{x:Type Border}">
etc...
and explicitly set your DataTemplate to use those styles:
<HierarchicalDataTemplate DataTemplate="TestElement">
<Border Height="45" Width="120" Margin="5,5", Style="{StaticResource BorderStyle}">
I think that it's possible that for DataTemplates (and maybe ControlTemplates), they default to having a null style, unless you explicitly set them.
That to me is not meant to happen - it's not a logical way of WPF working...

This is because ListBox is a logical parent of your datatemplate items, now remember, all properties those are "inheritable" like font, forecolor etc, are derived from the logical parent and ListBox already overrides it in its own default style, thats why this will not work. However in this case, you can use named styles as Mr. Dave has suggested, but I think if it does not work then this is a known problem in case of List Box etc, you can refere to my question here, i had similar problem in listbox, and the answers in my question are in more detail.

ListView items from an ObservableCollection that need to prepare themselves for realization

I have a ListView which is supposed to display a rather large number of items comprised of a "Name", a "Thumbnail" and a "AnimationPosition" property. A background task in each item's type is in charge of switching the thumbnails in order to animate them.
Now it goes without saying that this is a rather heavy operation and should be limited to as few items as possible e.g. to visible/realizing items of a Virtualized ListView. Now I already have set the DataContext of my ListView to the ObeservableCollection instance and have bound it to the properties of its type. Here's a peek into my XAML code for that.
<TabControl Grid.Row="0" Grid.Column="2">
<TabControl.Resources>
<Style x:Key="MediaItemStyle" TargetType="{x:Type ListViewItem}">
<Setter Property="Margin" Value="5,5,5,5"/>
<Setter Property="Padding" Value="0,0,0,0"/>
<Setter Property="HorizontalAlignment" Value="Left"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ListViewItem}">
<Grid HorizontalAlignment="Left" VerticalAlignment="Top" Height="Auto" >
<Border x:Name="border" BorderBrush="{x:Null}" BorderThickness="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" CornerRadius="2.5"/>
<StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<ContentPresenter/>
</StackPanel>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style TargetType="custom:MediaContainerListView">
<Setter Property="ItemsSource" Value="{Binding}"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Disabled"/>
<Setter Property="ItemContainerStyle" Value="{StaticResource MediaItemStyle}"/>
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<WrapPanel/>
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
<Setter Property="ItemTemplate">
<Setter.Value>
<DataTemplate>
<DockPanel Width="256">
<Image DockPanel.Dock="Top" Height="144" StretchDirection="Both"
Stretch="Fill" Source="{Binding Thumbnail.Source,Mode=OneWay}"/>
<ProgressBar DockPanel.Dock="Top" Height="2"
Minimum="0" Maximum="{Binding Thumbnail.AnimationPosition.Length}"
Value="{Binding Thumbnail.AnimationPosition.Position}"
Visibility="{Binding Thumbnail.AnimationPosition.Visibility}"/>
<TextBlock DockPanel.Dock="Bottom" Height="40"
TextWrapping="Wrap" TextTrimming="CharacterEllipsis"
TextAlignment="Center" Text="{Binding Name}"/>
</DockPanel>
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
</TabControl.Resources>
<TabItem Header="">
<custom:MediaContainerListView x:Name="MediaContainerView"></custom:MediaContainerListView>
</TabItem>
</TabControl>
Basically, I have two methods that start/stop the animation for each individual item.
public async void StartAnimation()
{
if( Count > 1 )
{
Task thumbnailAnimationTask = AnimationTask( AnimationCancellationToken.Token );
await thumbnailAnimationTask;
}
}
public void StopAnimation()
{
AnimationCancellationToken.Cancel();
}
I have two issues here.
The ListView seems to realize all the items rather than only those visible or within the realization range. I suspect my XAML somehow kills the Virtualization and have tried many solutions with no success. Mind you I need my ListView to be scalable to the MainWindow's dimensions and not be of fixed hight and width.
I need to call StartAnimation when an item is about to be realized and StopAnimation when it has left the view.
Even though my ListView is not correctly Virtualized, if my understanding of how ObservableCollections work is correct, it's only the UI representation of the items that are managed by the Virtualization and not the items themselves i.e. calling the StartAnimation/StopAnimation from the Constructor/Destructor of the items don't help much as they are called for every single item at the time of creation anyway.
Is there a neat way to somehow inform each item that they are about to be realized or leave the ListView view?
Update:
The issue of virtualizing not working correctly was related to the WrapPanel and once I switched to VirtualizingStackPanel it started to work correctly. Unfortunately it's not exactly the same as a WrapPanel and since .NET framework does not offer a VirtualizingWrapPanel, I chose to use the one from here. It's not perfect but it does the job.

You said it was 1/2
Look for a call to GetHashcode
I think it calls it GetHashcode just to find it
By accident I discovered it is called when the item is virtualized
Have an animation that terminates (does not loop)

I finally solved the problem myself. I knew it wouldn't have to be so complicated and it really isn't. Since I already had created my own ListView inherited class called MediaContainerListView, I could override a few of its virtual methods. Two of them proved to be just what I wanted.
protected override void PrepareContainerForItemOverride( DependencyObject element, object item )
which is called just before the item is about to appear, and
protected override void ClearContainerForItemOverride( DependencyObject element, Object item )
which is called just before the item is about to disappear. So I call the StartAnimation in the first one and the StopAnimation in the second one and it works flawlessly!

Using BasedOn and Trigger to manipulate nested property in parent Style

We have a file of standard styles. One style, SectionGroup, we use on all our GroupBox elements. It has a custom template which uses a Border to put an underline below the header, among other things.
On one page, we have a checkbox next to a GroupBox header; when the user unchecks the checkbox, the contents of the GroupBox hide (visibility collapsed) and the header remains. Unfortunately the underline under the header then looks ugly; we also want to hide this.
I've given it my best attempt, so the parent SectionGroup style now looks like this:
<Style x:Key="SectionGroup" TargetType="GroupBox">
<Style.Resources>
<Thickness x:Key="HeaderBorderThickness">0,0,0,1</Thickness>
</Style.Resources>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="GroupBox">
<Grid Margin="0">
...
<Border Grid.Row="0" BorderThickness="{DynamicResource HeaderBorderThickness}" >
<TextBlock Text="{Binding Header, RelativeSource={RelativeSource AncestorType=GroupBox}}"/>
</Border>
...
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
By defining the HeaderBorderThickness resource and using it as a DynamicResource, I can override it in my page (as explained in this answer):
<GroupBox>
<GroupBox.Style>
<Style TargetType="GroupBox" BasedOn="{StaticResource SectionGroup}">
<Style.Resources>
<Thickness x:Key="HeaderBorderThickness">0,0,0,0</Thickness>
</Style.Resources>
<!-- TODO triggers here.. -->
</Style>
</GroupBox.Style>
<GroupBox.Header>Section One</GroupBox.Header>
...contents...
</GroupBox>
So indeed, by redefining a Thickness of the same key, the DynamicResource works as expected and there is no underline on the header.
Now I need to toggle it based on a trigger/binding. I'm pretty new to this, but elsewhere in this page I have figured out to do stuff like this:
<Grid Visibility="{Binding Path=FooBoolean, Converter={StaticResource BooleanToVisibility}}">
I think there's a little more magic involved in our viewmodel class (followed the example of existing bindings & properties), but it works.
Now the question is -- how do I bind the boolean value in FooBoolean, to the HeaderBorderThickness resource value? Or what other means can I use to accomplish my goal?

It seems to me that you could do this in a much more WPF way with a DataTrigger, perhaps something like this:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<TextBlock Text="{Binding Header, RelativeSource={RelativeSource AncestorType=
GroupBox}}"/>
<Rectangle Grid.Row="1" Height="1" Margin="0,2,0,0" Fill="Black">
<Rectangle.Style>
<Style>
<Setter Property="Rectangle.Visibility" Value="Visible" />
<Style.Triggers>
<DataTrigger Binding="{IsChecked, ElementName=YourCheckBox}"
Value="False">
<Setter Property="Rectangle.Visibility" Value="Collapsed" />
</DataTrigger>
</Style.Triggers>
</Style>
</Rectangle.Style>
</Rectangle>
</Grid>
This method enables you to set the Width, Height, Padding and whatever other properties of the line. If you can't access the CheckBox directly from the Style, then you could try adding a bool property to bind to both the Checkbox.IsChecked property and the DataTrigger.Binding property. Or just manage the Rectangle.Visibility in your own method.

Reusable way to put a bright red box around whatever element currently has focus?

I've got some windows with mainly comboboxes, textboxes, and checkboxes. When you click on one to get focus I need a way to have them be outlined with a colorful box (boss' orders). Is there a way to do this easier than overriding the default style of all of these controls? I've never done that before, so it would take a lot of mucking around on my part to figure it out.

You can try adding a FocusVisualStyle to the Controls that need different focus rectangle styles.
From above link
The second mechanism is to provide a separate style as the value of the FocusVisualStyle property; the "focus visual style" creates a separate visual tree for an adorner that draws on top of the control, rather than changing the visual tree of the control or other UI element by replacing it.
Something like this in your Window's Xaml
<Window.Resources>
<Style x:Key="NewFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border>
<Rectangle Stroke="Red" Margin="2" StrokeThickness="1" StrokeDashArray="1 2" />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
or your Application.Xaml file.
<Application.Resources>
<Style x:Key="NewFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border>
<Rectangle Stroke="Red" Margin="2" StrokeThickness="1" StrokeDashArray="1 2" />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Application.Resources>
Usage:
<ComboBox FocusVisualStyle="{StaticResource NewFocusVisual}" Height="23" HorizontalAlignment="Left" Margin="238,102,0,0" Name="ComboBox1" VerticalAlignment="Top" Width="120" />
<CheckBox FocusVisualStyle="{StaticResource NewFocusVisual}" Content="CheckBox" Height="16" HorizontalAlignment="Left" Margin="238,71,0,0" Name="CheckBox2" VerticalAlignment="Top" />
<TextBox FocusVisualStyle="{StaticResource NewFocusVisual}" Height="23" HorizontalAlignment="Left" Margin="238,144,0,0" Name="TextBox1" VerticalAlignment="Top" Width="120" />
If you want the Focus rectangle to change for every type of focus event Microsoft states that:
From Microsoft: Focus visual styles act exclusively for keyboard focus. As such, focus visual styles are a type of accessibility feature. If you want UI changes for any type of focus, whether via mouse, keyboard, or programmatically, then you should not use focus visual styles, and should instead use setters and triggers in styles or templates that are working from the value of general focus properties such as IsFocused or IsFocusWithin.
Give this a shot it works for a TextBox haven't checked your other Controls
<Application.Resources>
<Style TargetType="TextBox" >
<Style.Triggers>
<Trigger Property="IsFocused" Value="True">
<Setter Property="Control.BorderBrush" Value="Red" />
<Setter Property="Control.BorderThickness" Value="3" />
</Trigger>
</Style.Triggers>
</Style>
</Application.Resources>

WPF Custom control guidance - horizontal tree

I've been asked to create a new control for a feature that we need, I'm really struggling on how to best achieve this in a generic and flexible way.
basically the control is very similar to a tree view, where as you would click on a node and then its children would then appear underneath that node.
for this control, they want it like this - when you click on a node, its children are then displayed on the left of parents container and so on.
I've done a quick (super quick) diagram in paint... (please don't laugh, its terrible! :) )
So you should just start with a single list of items and then progressive through the children of the selected item..
so my question is really, where do you start on something like this.. ? I'm fine with the data side but the XAML is the bit that's really confusing me, it needs to be very generic so it could potential cope with 100's of children panels
any help would be brilliant.
cheers.
ste.

If you are after a usercontrol and known bindings at designtime - it would be easy, but as a custom control - i'm very interested in good answers
like i said this can easy be done if you know the collection bindings and the childlevel. but its maybe a start to get a custom control.
<UserControl>
<UserControl.Resources>
<Style x:Key="{x:Type ListBox}" TargetType="{x:Type ListBox}">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="BorderThickness" Value="0"/>
<Setter Property="ItemContainerStyle">
<Setter.Value>
<Style TargetType="ListBoxItem">
<Setter Property="VerticalContentAlignment" Value="Stretch"></Setter>
</Style>
</Setter.Value>
</Setter>
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<UniformGrid Columns="1"/>
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
</Style>
<DataTemplate DataType="{x:Type local:TreeItems}">
<Grid VerticalAlignment="Stretch">
<Border BorderBrush="Black" BorderThickness="1" >
<TextBlock Margin="5" Text="{Binding Name}"/>
</Border>
</Grid>
</DataTemplate>
</UserControl.Resources>
<StackPanel Orientation="Horizontal">
<ListBox x:Name="root" ItemsSource="{Binding}"></ListBox>
<ListBox x:Name="Lvl1" ItemsSource="{Binding ElementName=root, Path=SelectedItem.Childs}" />
<ListBox x:Name="Lvl2" ItemsSource="{Binding ElementName=Lvl1, Path=SelectedItem.Childs}" />
</StackPanel>
</UserControl>

This article from Josh Smith is a good starting point.
If all you need is a hierarchical data control, you better use a TreeView and not rolling your own control, as it is probably more complicated than you think (selection, keyboard navigation, etc.)