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Custom ComboBox Style not showing SelectedItem

I am styling a ComboBox, I just copy-paste the default style and changes some stuff already. The problem I have is that the SelectedItem is not being shown.
Maybe a xaml Guru can help me out to find th error.
The combobox will not be editable, so I guess the problem is in the ContentSite but I am not pretty sure how I can make it work.
Thanks in advance!
EDIT:
I have already check that there is a SelectedItem, if I use a normal ComboBox, the item is shown.
CurrentStyle:
<ControlTemplate x:Key="ToggleButton"
TargetType="{x:Type ToggleButton}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="50" />
</Grid.ColumnDefinitions>
<Border x:Name="Border"
Grid.ColumnSpan="2"
Background="{StaticResource ColorMagnoscoGreen}"
BorderBrush="#FF97A0A5"
BorderThickness="1"
CornerRadius="0" />
<Border Grid.Column="0"
Margin="1"
Background="White"
BorderThickness="1"
CornerRadius="0" />
<Path x:Name="Arrow"
Grid.Column="1"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M0,0 L0,2 L4,6 L8,2 L8,0 L4,4 z"
Fill="White" />
</Grid>
</ControlTemplate>
<ControlTemplate x:Key="ComboBoxTextBox"
TargetType="{x:Type TextBox}">
<Border x:Name="PART_ContentHost"
BorderThickness="1"
Focusable="False">
</Border>
</ControlTemplate>
<Style x:Key="{x:Type ComboBox}"
TargetType="{x:Type ComboBox}">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.CanContentScroll" Value="true" />
<Setter Property="MinWidth" Value="120" />
<Setter Property="MinHeight" Value="40" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<ContentPresenter x:Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="3,3,23,3"
VerticalAlignment="Stretch"
HorizontalAlignment="Left">
</ContentPresenter>
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Bottom"
Margin="3,3,23,3"
Focusable="True"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}" />
<Popup Name="Popup"
AllowsTransparency="False"
Focusable="False"
IsOpen="{TemplateBinding IsDropDownOpen}"
Placement="Bottom"
PopupAnimation="Slide">
<Grid Name="DropDown"
Background="White"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}"
SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder"
BorderBrush="#888888"
BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6"
SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True"
KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
<ToggleButton Name="ToggleButton"
Grid.Column="2"
ClickMode="Press"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
Template="{StaticResource ComboBoxToggleButton}" />
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95" />
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#888888" />
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false" />
</Trigger>
<Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
<Setter TargetName="DropDownBorder" Property="CornerRadius" Value="0" />
<Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0" />
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false" />
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible" />
<Setter TargetName="ContentSite" Property="Visibility" Value="Hidden" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="{x:Type ComboBoxItem}"
TargetType="{x:Type ComboBoxItem}">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="Foreground" Value="Black" />
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="FontSize" Value="16"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBoxItem}">
<Border Name="Border"
Padding="2"
SnapsToDevicePixels="true">
<ContentPresenter />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsHighlighted" Value="true">
<Setter TargetName="Border" Property="Background" Value="{StaticResource ColorMagnoscoGreen}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

The ToggleButton hides the ContentPresenter in the ControlTemplate. Move the ContentPresenter below the ToggleButton:
<Grid>
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Bottom"
Margin="3,3,23,3"
Focusable="True"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}" />
<Popup Name="Popup"
AllowsTransparency="False"
Focusable="False"
IsOpen="{TemplateBinding IsDropDownOpen}"
Placement="Bottom"
PopupAnimation="Slide">
<Grid Name="DropDown"
Background="White"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}"
SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder"
BorderBrush="#888888"
BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
<ToggleButton Name="ToggleButton"
Grid.Column="2"
ClickMode="Press"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
Template="{StaticResource ComboBoxToggleButton}" />
<ContentPresenter x:Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="3,3,23,3"
VerticalAlignment="Stretch"
HorizontalAlignment="Left">
</ContentPresenter>
</Grid>

HorizontalAlignment="Stretch" not working in TreeViewItem

Here's an example where it is not working:
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApplication2"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<TreeView HorizontalAlignment="Stretch">
<TreeViewItem Header="Stuff" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch">
<Grid HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0">Some random text</Label>
<TextBox Grid.Column="1"></TextBox>
</Grid>
</TreeViewItem>
</TreeView>
</Window>
I want the text box to stretch to the width of the window, but instead you get this:
The textbox expands as you type, which is not what I want.
I am thinking now it might be possible to set a binding on the width of the 2nd column to the width of the TreeViewItem but I'm not sure how to do that.
I've tried putting the grid in assorted panels, but that doesn't work either. I have also set the HorizontalAlignment and HorizontalContentAlignment to Stretch on the textbox itself, but that also doesn't work.
Is this some limitation of the Grid control? Putting a textbox in a tree view by itself will make it expand as I want, but I need the label to be next to it and if there are multiple fields it looks MUCH better if all the textboxes are aligned.
UPDATE
Using a different ControlTemplate allows headers to stretch but contents still don't stretch.
<TreeView HorizontalAlignment="Stretch">
<TreeViewItem Style="{DynamicResource StretchableTreeViewItemTemplate}" HorizontalAlignment="Stretch" Header="Stuff">
<Grid HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0">Some random text</Label>
<TextBox Grid.Column="1" HorizontalAlignment="Stretch"></TextBox>
</Grid>
</TreeViewItem>
</TreeView>
<Style x:Key="StretchableTreeViewItemTemplate" TargetType="TreeViewItem"
BasedOn="{StaticResource {x:Type TreeViewItem}}">
<Setter Property="HorizontalContentAlignment"
Value="Center" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TreeViewItem">
<StackPanel>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"
MinWidth="19" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<!--
Note that the following do not work, but I believe the top 2 should?!
<ToggleButton IsChecked="{TemplateBinding IsExpanded}" ClickMode="Press" Name="Expander">
<ToggleButton IsChecked="{TemplateBinding Property=IsExpanded}" ClickMode="Press" Name="Expander">
<ToggleButton IsChecked="{TemplateBinding Path=IsExpanded}" ClickMode="Press" Name="Expander">
-->
<ToggleButton IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"
Name="Expander">
<ToggleButton.Style>
<Style TargetType="ToggleButton">
<Setter Property="UIElement.Focusable"
Value="false" />
<Setter Property="FrameworkElement.Width"
Value="16" />
<Setter Property="FrameworkElement.Height"
Value="16" />
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="5,5,5,5"
Background="#00FFFFFF"
Width="16"
Height="16">
<Path Fill="#00FFFFFF"
Stroke="#FF989898"
Name="ExpandPath">
<Path.Data>
<PathGeometry Figures="M0,0L0,6L6,0z" />
</Path.Data>
<Path.RenderTransform>
<RotateTransform Angle="135"
CenterX="3"
CenterY="3" />
</Path.RenderTransform>
</Path>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="UIElement.IsMouseOver"
Value="True">
<Setter TargetName="ExpandPath"
Property="Shape.Stroke"
Value="#FF1BBBFA" />
<Setter TargetName="ExpandPath"
Property="Shape.Fill"
Value="#00FFFFFF" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked"
Value="True">
<Setter TargetName="ExpandPath"
Property="UIElement.RenderTransform">
<Setter.Value>
<RotateTransform Angle="180"
CenterX="3"
CenterY="3" />
</Setter.Value>
</Setter>
<Setter TargetName="ExpandPath"
Property="Shape.Fill"
Value="#FF595959" />
<Setter TargetName="ExpandPath"
Property="Shape.Stroke"
Value="#FF262626" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
</ToggleButton>
<Border x:Name="Bd"
HorizontalAlignment="Stretch"
BorderThickness="{TemplateBinding Border.BorderThickness}"
BorderBrush="{TemplateBinding Border.BorderBrush}"
Padding="{TemplateBinding Control.Padding}"
Background="{TemplateBinding Panel.Background}"
SnapsToDevicePixels="True"
Grid.Column="1">
<ContentPresenter x:Name="PART_Header"
Content="{TemplateBinding HeaderedContentControl.Header}"
ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}"
ContentStringFormat="{TemplateBinding HeaderedItemsControl.HeaderStringFormat}"
ContentTemplateSelector="{TemplateBinding HeaderedItemsControl.HeaderTemplateSelector}"
ContentSource="Header"
HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
</Border>
<ItemsPresenter x:Name="ItemsHost"
Grid.Column="1"
Grid.Row="1" />
</Grid>
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="TreeViewItem.IsExpanded"
Value="False">
<Setter TargetName="ItemsHost"
Property="UIElement.Visibility"
Value="Collapsed" />
</Trigger>
<Trigger Property="ItemsControl.HasItems"
Value="False">
<Setter TargetName="Expander"
Property="UIElement.Visibility"
Value="Hidden" />
</Trigger>
<Trigger Property="TreeViewItem.IsSelected"
Value="True">
<Setter TargetName="Bd"
Property="Panel.Background"
Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}" />
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="TreeViewItem.IsSelected"
Value="True" />
<Condition Property="Selector.IsSelectionActive"
Value="False" />
</MultiTrigger.Conditions>
<Setter TargetName="Bd"
Property="Panel.Background"
Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" />
</MultiTrigger>
<Trigger Property="UIElement.IsEnabled"
Value="False">
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Results:
Trying with Pikoh's solution:
<local:StretchingTreeView HorizontalAlignment="Stretch">
<local:StretchingTreeViewItem HorizontalAlignment="Stretch" Header="Stuff">
<Grid HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0">Some random text</Label>
<TextBox Grid.Column="1" HorizontalAlignment="Stretch"></TextBox>
</Grid>
</local:StretchingTreeViewItem>
</local:StretchingTreeView>

Try something like this:
<TextBox Grid.Column="1" Width="{Binding Path=ActualWidth, RelativeSource={RelativeSource AncestorType={x:Type Grid}}, Mode=OneWay}"></TextBox>
Edit
Ok,i've found one solution Here. It basically creates a new class inheriting Treeview:
class StretchingTreeView : TreeView
{
protected override DependencyObject GetContainerForItemOverride()
{
return new StretchingTreeViewItem();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is StretchingTreeViewItem;
}
}
class StretchingTreeViewItem : TreeViewItem
{
public StretchingTreeViewItem()
{
this.Loaded += new RoutedEventHandler(StretchingTreeViewItem_Loaded);
}
private void StretchingTreeViewItem_Loaded(object sender, RoutedEventArgs e)
{
// The purpose of this code is to stretch the Header Content all the way accross the TreeView.
if (this.VisualChildrenCount > 0)
{
Grid grid = this.GetVisualChild(0) as Grid;
if (grid != null && grid.ColumnDefinitions.Count == 3)
{
// Remove the middle column which is set to Auto and let it get replaced with the
// last column that is set to Star.
grid.ColumnDefinitions.RemoveAt(1);
}
}
}
protected override DependencyObject GetContainerForItemOverride()
{
return new StretchingTreeViewItem();
}
protected override bool IsItemItsOwnContainerOverride(object item)
{
return item is StretchingTreeViewItem;
}
}
Example usage:
<Window x:Class="WpfApplication2.Window2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication2"
Title="Window2" Height="300" Width="300">
<Grid>
<local:StretchingTreeView HorizontalAlignment="Stretch" >
<local:StretchingTreeViewItem Header="Stuff" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch" >
<Grid HorizontalAlignment="Stretch" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0">Some random text</Label>
<TextBox Grid.Column="1" ></TextBox>
</Grid>
</local:StretchingTreeViewItem>
</local:StretchingTreeView>
</Grid>

The core of the issue (and the way to fix it) is described here:
The default ControlTemplate for the TreeViewItem uses a grid of 3 columns x 2 rows, defined such that the content cannot stretch horizontally. The author also gives a modified style, that changes the grid so that the content can stretch.
Note that the modified style sets the HorizontalContentAlignment of TreeViewItem to Center, and that the ControlTemplate uses this property for aligning the content.
To achieve the desired effect, either set HorizontalContentAlignment to Stretch in the modified style, or override just that property on the TreeView (or specific TreeViewItems).
Missing the BasedOn="{StaticResource {x:Type TreeViewItem}}" part causes the TreeViewItem to revert to using the default ControlTemplate, with the non-stretchable grid.
<Style TargetType="TreeViewItem" BasedOn="{StaticResource {x:Type TreeViewItem}}">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
</Style>
In a HierarchicalDataTemplate, the effect would be achieved by using the ItemContainerStyle property.
#pikoh's method of deriving from TreeView and TreeViewItem achieves the same, by modifying the grid from code.
Complete example:
<Window x:Class="WpfApp1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.Resources>
<Style TargetType="TreeViewItem" BasedOn="{StaticResource {x:Type TreeViewItem}}">
<Setter Property="HorizontalContentAlignment" Value="Center" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TreeViewItem">
<StackPanel>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"
MinWidth="19" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<!-- Note that the following do not work, but I believe the top 2 should?! -->
<ToggleButton IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press" Name="Expander">
<ToggleButton.Style>
<Style TargetType="ToggleButton">
<Setter Property="UIElement.Focusable" Value="false" />
<Setter Property="FrameworkElement.Width" Value="16" />
<Setter Property="FrameworkElement.Height" Value="16" />
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="5,5,5,5" Background="#00FFFFFF" Width="16" Height="16">
<Path Fill="#00FFFFFF" Stroke="#FF989898" Name="ExpandPath">
<Path.Data>
<PathGeometry Figures="M0,0L0,6L6,0z" />
</Path.Data>
<Path.RenderTransform>
<RotateTransform Angle="135" CenterX="3" CenterY="3" />
</Path.RenderTransform>
</Path>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="UIElement.IsMouseOver" Value="True">
<Setter TargetName="ExpandPath" Property="Shape.Stroke" Value="#FF1BBBFA" />
<Setter TargetName="ExpandPath" Property="Shape.Fill" Value="#00FFFFFF" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="True">
<Setter TargetName="ExpandPath" Property="UIElement.RenderTransform">
<Setter.Value>
<RotateTransform Angle="180" CenterX="3" CenterY="3" />
</Setter.Value>
</Setter>
<Setter TargetName="ExpandPath" Property="Shape.Fill" Value="#FF595959" />
<Setter TargetName="ExpandPath" Property="Shape.Stroke" Value="#FF262626" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
</ToggleButton>
<Border x:Name="Bd"
HorizontalAlignment="Stretch"
BorderThickness="{TemplateBinding Border.BorderThickness}"
BorderBrush="{TemplateBinding Border.BorderBrush}"
Padding="{TemplateBinding Control.Padding}"
Background="{TemplateBinding Panel.Background}"
SnapsToDevicePixels="True"
Grid.Column="1">
<ContentPresenter x:Name="PART_Header"
Content="{TemplateBinding HeaderedContentControl.Header}"
ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}"
ContentStringFormat="{TemplateBinding HeaderedItemsControl.HeaderStringFormat}"
ContentTemplateSelector="{TemplateBinding HeaderedItemsControl.HeaderTemplateSelector}"
ContentSource="Header"
HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
</Border>
<ItemsPresenter x:Name="ItemsHost" Grid.Column="1" Grid.Row="1" />
</Grid>
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="TreeViewItem.IsExpanded" Value="False">
<Setter TargetName="ItemsHost" Property="UIElement.Visibility" Value="Collapsed" />
</Trigger>
<Trigger Property="ItemsControl.HasItems" Value="False">
<Setter TargetName="Expander" Property="UIElement.Visibility" Value="Hidden" />
</Trigger>
<Trigger Property="TreeViewItem.IsSelected" Value="True">
<Setter TargetName="Bd" Property="Panel.Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
<Setter Property="TextElement.Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}" />
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="TreeViewItem.IsSelected" Value="True" />
<Condition Property="Selector.IsSelectionActive" Value="False" />
</MultiTrigger.Conditions>
<Setter TargetName="Bd" Property="Panel.Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />
<Setter Property="TextElement.Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" />
</MultiTrigger>
<Trigger Property="UIElement.IsEnabled" Value="False">
<Setter Property="TextElement.Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<TreeView HorizontalAlignment="Stretch">
<TreeView.Resources>
<Style TargetType="TreeViewItem" BasedOn="{StaticResource {x:Type TreeViewItem}}">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
</Style>
</TreeView.Resources>
<TreeViewItem Header="Stuff" HorizontalAlignment="Stretch">
<Grid HorizontalAlignment="Stretch">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0">Some random text</Label>
<TextBox Grid.Column="1"></TextBox>
</Grid>
</TreeViewItem>
</TreeView>
</Window>

Due to an odd design decision by Microsoft when creating WPF, tree items can't stretch without replacing the control template.
See http://leecampbell.blogspot.com/2009/01/horizontal-stretch-on-treeviewitems.html
The required style is:
<Style TargetType="TreeViewItem"
BasedOn="{StaticResource {x:Type TreeViewItem}}">
<Setter Property="HorizontalContentAlignment"
Value="Center" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TreeViewItem">
<StackPanel>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"
MinWidth="19" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<!--
Note that the following do not work, but I believe the top 2 should?!
<ToggleButton IsChecked="{TemplateBinding IsExpanded}" ClickMode="Press" Name="Expander">
<ToggleButton IsChecked="{TemplateBinding Property=IsExpanded}" ClickMode="Press" Name="Expander">
<ToggleButton IsChecked="{TemplateBinding Path=IsExpanded}" ClickMode="Press" Name="Expander">
-->
<ToggleButton IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"
Name="Expander">
<ToggleButton.Style>
<Style TargetType="ToggleButton">
<Setter Property="UIElement.Focusable"
Value="false" />
<Setter Property="FrameworkElement.Width"
Value="16" />
<Setter Property="FrameworkElement.Height"
Value="16" />
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="5,5,5,5"
Background="#00FFFFFF"
Width="16"
Height="16">
<Path Fill="#00FFFFFF"
Stroke="#FF989898"
Name="ExpandPath">
<Path.Data>
<PathGeometry Figures="M0,0L0,6L6,0z" />
</Path.Data>
<Path.RenderTransform>
<RotateTransform Angle="135"
CenterX="3"
CenterY="3" />
</Path.RenderTransform>
</Path>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="UIElement.IsMouseOver"
Value="True">
<Setter TargetName="ExpandPath"
Property="Shape.Stroke"
Value="#FF1BBBFA" />
<Setter TargetName="ExpandPath"
Property="Shape.Fill"
Value="#00FFFFFF" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked"
Value="True">
<Setter TargetName="ExpandPath"
Property="UIElement.RenderTransform">
<Setter.Value>
<RotateTransform Angle="180"
CenterX="3"
CenterY="3" />
</Setter.Value>
</Setter>
<Setter TargetName="ExpandPath"
Property="Shape.Fill"
Value="#FF595959" />
<Setter TargetName="ExpandPath"
Property="Shape.Stroke"
Value="#FF262626" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
</ToggleButton>
<Border x:Name="Bd"
HorizontalAlignment="Stretch"
BorderThickness="{TemplateBinding Border.BorderThickness}"
BorderBrush="{TemplateBinding Border.BorderBrush}"
Padding="{TemplateBinding Control.Padding}"
Background="{TemplateBinding Panel.Background}"
SnapsToDevicePixels="True"
Grid.Column="1">
<ContentPresenter x:Name="PART_Header"
Content="{TemplateBinding HeaderedContentControl.Header}"
ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}"
ContentStringFormat="{TemplateBinding HeaderedItemsControl.HeaderStringFormat}"
ContentTemplateSelector="{TemplateBinding HeaderedItemsControl.HeaderTemplateSelector}"
ContentSource="Header"
HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
</Border>
<ItemsPresenter x:Name="ItemsHost"
Grid.Column="1"
Grid.Row="1" />
</Grid>
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="TreeViewItem.IsExpanded"
Value="False">
<Setter TargetName="ItemsHost"
Property="UIElement.Visibility"
Value="Collapsed" />
</Trigger>
<Trigger Property="ItemsControl.HasItems"
Value="False">
<Setter TargetName="Expander"
Property="UIElement.Visibility"
Value="Hidden" />
</Trigger>
<Trigger Property="TreeViewItem.IsSelected"
Value="True">
<Setter TargetName="Bd"
Property="Panel.Background"
Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}" />
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="TreeViewItem.IsSelected"
Value="True" />
<Condition Property="Selector.IsSelectionActive"
Value="False" />
</MultiTrigger.Conditions>
<Setter TargetName="Bd"
Property="Panel.Background"
Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" />
</MultiTrigger>
<Trigger Property="UIElement.IsEnabled"
Value="False">
<Setter Property="TextElement.Foreground"
Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

It seems like Grid's HorizontalAlignment Issue. I've tried it in .Net Framework 4 and it all works fine. Seems like in 4.5 even though you specify HorizontalAlignment as Stretch, it actually doesn't stretch it. So you can do a binding like below:
<Grid HorizontalAlignment="Stretch"
Width="{Binding RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}},Path=ActualWidth,Mode=OneTime}"
>
Cause you can see in the run time that TreeViewItem has Width expected but Grid doesn't.

All you need to do is add Grid.ColumnSpan='2' to the ControlTemplate of the TreeViewItem as shown below.
Thats it!
Explanation:
The default ControlTemplate places the Header Content in a Grid column that does not stretch. The Grid.ColumnSpan='2' instructs the Header content to span to the rest of the Grid.

Add Controllers to <Style> from Code-Behind (WPF)

I'm a beginner in WPF. It's hard as hell just so you know!
ok, i have a little style for my application (Actually i copied it, and really don't know whats happening in the middle so...)
i wanted to add some Hyperlinks and Buttons to header of application. so i edited the style and added those from there.
but now i want to change content of those from code-behind, but as you already know that's not happening!
This is my style in Application.Resources:
<BooleanToVisibilityConverter x:Key="bool2VisibilityConverter" />
<Color x:Key="WindowBackgroundColor">#FF2D2D30</Color>
<Color x:Key="HighlightColor">Orange</Color>
<Color x:Key="BlueColor">AntiqueWhite</Color>
<Color x:Key="ForegroundColor">#FFF4F4F5</Color>
<SolidColorBrush x:Key="WindowBackgroundColorBrush" Color="{StaticResource WindowBackgroundColor}"/>
<SolidColorBrush x:Key="HighlightColorBrush" Color="{StaticResource HighlightColor}"/>
<SolidColorBrush x:Key="BlueColorBrush" Color="{StaticResource BlueColor}"/>
<SolidColorBrush x:Key="ForegroundColorBrush" Color="{StaticResource ForegroundColor}"/>
<Style x:Key="WindowButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Foreground" Value="{DynamicResource ForegroundColorBrush}" />
<Setter Property="Background" Value="Transparent" />
<Setter Property="HorizontalContentAlignment" Value="Center" />
<Setter Property="VerticalContentAlignment" Value="Center" />
<Setter Property="Padding" Value="1" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Grid Background="{TemplateBinding Background}">
<ContentPresenter x:Name="contentPresenter"
HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
Margin="{TemplateBinding Padding}"
RecognizesAccessKey="True" />
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="{StaticResource HighlightColorBrush}" />
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Background" Value="{DynamicResource BlueColorBrush}" />
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter TargetName="contentPresenter" Property="Opacity" Value=".5" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="{x:Type Hyperlink}" TargetType="Hyperlink">
<Setter Property="TextDecorations" Value="{x:Null}"/>
<Setter Property="Foreground" Value="#FFF4F4F5"/>
<Setter Property="FontSize" Value="14"/>
</Style>
<Style x:Key="MyWindowStyle" TargetType="local:MainWindow">
<Setter Property="Foreground" Value="{DynamicResource ForegroundColorBrush}" />
<Setter Property="Background" Value="{DynamicResource WindowBackgroundBrush}"/>
<Setter Property="ResizeMode" Value="NoResize" />
<Setter Property="UseLayoutRounding" Value="True" />
<Setter Property="TextOptions.TextFormattingMode" Value="Display" />
<Setter Property="WindowChrome.WindowChrome">
<Setter.Value>
<WindowChrome CornerRadius="0" GlassFrameThickness="1" UseAeroCaptionButtons="False"/>
</Setter.Value>
</Setter>
<Setter Property="WindowChrome.IsHitTestVisibleInChrome" Value="True"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:MainWindow">
<Border x:Name="WindowBorder" Margin="{Binding Source={x:Static SystemParameters.WindowNonClientFrameThickness}}" Background="{StaticResource WindowBackgroundColorBrush}">
<Grid>
<Border BorderThickness="1">
<AdornerDecorator>
<Grid x:Name="LayoutRoot">
<Grid.RowDefinitions>
<RowDefinition Height="27" />
<RowDefinition Height="*" />
<RowDefinition Height="15" />
</Grid.RowDefinitions>
<ContentPresenter Grid.Row="1" Grid.RowSpan="2" Margin="7"/>
<Image Width="30" Height="30" />
<!-- This is where i want put those Hyperlinks and the Button -->
<TextBlock Margin="50,5,0,0">
<Hyperlink NavigateUri="SupportPage.xaml" RequestNavigate="Hyperlink_Support">Support</Hyperlink>
</TextBlock>
<TextBlock Margin="122,5,0,0">
<Hyperlink NavigateUri="HelpPage.xaml" RequestNavigate="Hyperlink_Help">Support</Hyperlink>
</TextBlock>
<Button Name="btCustom" Content="btThatIWantChangeItsContent" VerticalAlignment="Bottom" HorizontalAlignment="Left"/>
<TextBlock Margin="220,5,0,0">
<Hyperlink NavigateUri="AboutPage.xaml" RequestNavigate="Hyperlink_About">About</Hyperlink>
</TextBlock>
<!-- to here -->
<Rectangle Mouse.MouseDown="rectangleMoveWindow_MouseDown" Margin="300,0,0,0" x:Name="HeaderBackground" Height="25" Fill="{DynamicResource WindowBackgroundColorBrush}" VerticalAlignment="Top" Grid.Row="0"/>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Right" VerticalAlignment="Top" WindowChrome.IsHitTestVisibleInChrome="True" Grid.Row="0">
<Button Command="{Binding Source={x:Static SystemCommands.MinimizeWindowCommand}}" ToolTip="minimize" Style="{StaticResource WindowButtonStyle}">
<Button.Content>
<Grid Width="30" Height="25" RenderTransform="1,0,0,1,0,1">
<Path Data="M0,6 L8,6 Z" Width="8" Height="7" VerticalAlignment="Center" HorizontalAlignment="Center"
Stroke="{Binding Foreground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Button}}" StrokeThickness="2" />
</Grid>
</Button.Content>
</Button>
<Grid Margin="1,0,1,0">
<Button x:Name="Restore" Command="{Binding Source={x:Static SystemCommands.RestoreWindowCommand}}" ToolTip="restore" Visibility="Collapsed" Style="{StaticResource WindowButtonStyle}">
<Button.Content>
<Grid Width="30" Height="25" UseLayoutRounding="True" RenderTransform="1,0,0,1,.5,.5">
<Path Data="M2,0 L8,0 L8,6 M0,3 L6,3 M0,2 L6,2 L6,8 L0,8 Z" Width="8" Height="8" VerticalAlignment="Center" HorizontalAlignment="Center"
Stroke="{Binding Foreground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Button}}" StrokeThickness="1" />
</Grid>
</Button.Content>
</Button>
<Button x:Name="Maximize" Command="{Binding Source={x:Static SystemCommands.MaximizeWindowCommand}}" ToolTip="maximize" Style="{StaticResource WindowButtonStyle}">
<Button.Content>
<Grid Width="31" Height="25">
<Path Data="M0,1 L9,1 L9,8 L0,8 Z" Width="9" Height="8" VerticalAlignment="Center" HorizontalAlignment="Center"
Stroke="{Binding Foreground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Button}}" StrokeThickness="2" />
</Grid>
</Button.Content>
</Button>
</Grid>
<Button Command="{Binding Source={x:Static SystemCommands.CloseWindowCommand}}" ToolTip="close" Style="{StaticResource WindowButtonStyle}">
<Button.Content>
<Grid Width="30" Height="25" RenderTransform="1,0,0,1,0,1">
<Path Data="M0,0 L8,7 M8,0 L0,7 Z" Width="8" Height="7" VerticalAlignment="Center" HorizontalAlignment="Center"
Stroke="{Binding Foreground, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Button}}" StrokeThickness="1.5" />
</Grid>
</Button.Content>
</Button>
</StackPanel>
<Grid Grid.Row="2">
<Path x:Name="ResizeGrip" Visibility="Collapsed" Width="12" Height="12" Margin="1" HorizontalAlignment="Right"
Stroke="{StaticResource BlueColorBrush}" StrokeThickness="1" Stretch="None" Data="F1 M1,10 L3,10 M5,10 L7,10 M9,10 L11,10 M2,9 L2,11 M6,9 L6,11 M10,9 L10,11 M5,6 L7,6 M9,6 L11,6 M6,5 L6,7 M10,5 L10,7 M9,2 L11,2 M10,1 L10,3" />
</Grid>
</Grid>
</AdornerDecorator>
</Border>
<Border BorderBrush="{StaticResource BlueColorBrush}" BorderThickness="1" Visibility="{Binding IsActive, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Converter={StaticResource bool2VisibilityConverter}}" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="WindowState" Value="Maximized">
<Setter TargetName="Maximize" Property="Visibility" Value="Collapsed" />
<Setter TargetName="Restore" Property="Visibility" Value="Visible" />
<Setter TargetName="LayoutRoot" Property="Margin" Value="7" />
</Trigger>
<Trigger Property="WindowState" Value="Normal">
<Setter TargetName="Maximize" Property="Visibility" Value="Visible" />
<Setter TargetName="Restore" Property="Visibility" Value="Collapsed" />
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="ResizeMode" Value="CanResizeWithGrip" />
<Condition Property="WindowState" Value="Normal" />
</MultiTrigger.Conditions>
<Setter TargetName="ResizeGrip" Property="Visibility" Value="Visible" />
</MultiTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
so i don't know how change content of Hyperlinks or even i could replace them with Button if that is necessary. just tell me how i could change those content. of course i have to say i tried FindResource but couldn't find that Hyperlinks or Buttons. Thanks in advance guys.

try this:
1. create a new WpfApplication project
2. remove MainWindow.xaml
3. add pages: startup.xaml, page1.xaml or more, and set diff background
4. change StartupUri="startup.xaml" in App.xaml
5. add NavigationWindow Style in App.xaml
<Style TargetType="{x:Type NavigationWindow}">
<Setter Property="OverridesDefaultStyle" Value="True"/>
<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type NavigationWindow}">
<Border Background="{TemplateBinding Background}">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<AdornerDecorator Grid.Row="1">
<ContentPresenter Name="PART_NavWinCP" ClipToBounds="true" />
</AdornerDecorator>
<StackPanel Grid.Row="0" Margin="20" Orientation="Horizontal">
<Label>
<Hyperlink NavigateUri="Page1.xaml">Page1</Hyperlink>
</Label>
</StackPanel>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

<StackPanel x:Name="panel" xmlns:sys="clr-namespace:System;assembly=mscorlib">
<StackPanel.Resources>
<sys:String x:Key="help">Support</sys:String>
</StackPanel.Resources>
<Label DataContext="{StaticResource help}">
<Hyperlink><TextBlock Text="{DynamicResource help}"/></Hyperlink>
</Label>
<Button Content="OK" Click="button_Click"/>
</StackPanel>
private void button_Click(object sender, RoutedEventArgs e)
{
panel.Resources["help"] = "Help";
}

Combo box style not showing selected item

I have been given a WPF application despite not knowing much about WPF.
I have a style for a combo box that looks really good but the items appear in the drop down list but the selected item is not appearing in the main text box that is shown when the drop down list is not shown. This simply remains empty.
I am pretty sure I nee to put a content presenter somewhere but the question is where?
I believe this is all of the code relating to this style.
<ControlTemplate x:Key="SearchActionComboBoxToggleButton" TargetType="{x:Type ToggleButton}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="20" />
</Grid.ColumnDefinitions>
<Border x:Name="Border"
Grid.ColumnSpan="2"
Background="Green"
BorderBrush="Black"
BorderThickness="2"
CornerRadius="3" />
<Border Grid.Column="0"
Margin="1"
Background="White"
BorderBrush="Black"
BorderThickness="1"
CornerRadius="0" />
<Path x:Name="Arrow"
Grid.Column="1"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M0,0 L0,2 L4,6 L8,2 L8,0 L4,4 z"
Fill="White" />
</Grid>
</ControlTemplate>
<Style x:Key="SearchActionComboBoxMenu" TargetType="ComboBox">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.CanContentScroll" Value="true" />
<Setter Property="Foreground" Value="White" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<ToggleButton Name="ToggleButton"
Grid.Column="2"
ClickMode="Press"
Cursor="Hand"
Focusable="false"
Foreground="Black"
IsChecked="{Binding Path=IsDropDownOpen,
Mode=TwoWay,
RelativeSource={RelativeSource TemplatedParent}}"
Template="{StaticResource SearchActionComboBoxToggleButton}" />
<TextBox x:Name="PART_EditableTextBox"
Margin="3,3,23,3"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Background="White"
Focusable="True"
Foreground="Black"
IsReadOnly="{TemplateBinding IsReadOnly}"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
Visibility="Hidden" />
<Popup Name="Popup"
Width="200"
AllowsTransparency="True"
Focusable="False"
IsOpen="{TemplateBinding IsDropDownOpen}"
Placement="Bottom"
PopupAnimation="Slide">
<Grid Name="DropDown"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}"
SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder"
Background="White"
BorderBrush="Black"
BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95" />
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#888888" />
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false" />
</Trigger>
<Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
<Setter TargetName="DropDownBorder" Property="CornerRadius" Value="0" />
<Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0" />
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false" />
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers />
</Style>
Please let me know if you need any of the other code that may be called that I havent supplied.

You havent set contentpresenter in style
<Style x:Key="SearchActionComboBoxMenu" TargetType="ComboBox">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.CanContentScroll" Value="true" />
<Setter Property="Foreground" Value="White" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<ToggleButton Name="ToggleButton" Grid.Column="2" ClickMode="Press" Cursor="Hand" Focusable="false" Foreground="Black" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}" Template="{StaticResource SearchActionComboBoxToggleButton}" />
//added contentpresenter here
<ContentPresenter x:Name="ContentSite" IsHitTestVisible="False" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" Margin="3,3,23,3" TextElement.Foreground="Red" VerticalAlignment="Stretch" HorizontalAlignment="Left"/>
<TextBox x:Name="PART_EditableTextBox" Margin="3,3,23,3" HorizontalAlignment="Left" VerticalAlignment="Center" Background="White" Focusable="True" Foreground="Black" IsReadOnly="{TemplateBinding IsReadOnly}" Style="{x:Null}" Visibility="Hidden" />
<Popup Name="Popup" Width="200" AllowsTransparency="True" Focusable="False" IsOpen="{TemplateBinding IsDropDownOpen}" Placement="Bottom" PopupAnimation="Slide">
<Grid Name="DropDown" MinWidth="{TemplateBinding ActualWidth}" MaxHeight="{TemplateBinding MaxDropDownHeight}" SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder" Background="White" BorderBrush="Black" BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
........................
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers />
</Style>

XAML ComboBox DataTemplate popup not showing on click

I have a custom ComboBox defined in a resource xaml file. Everything's working fine, but the drop down only shows if I focus on the combobox and then press alt-dn. I really want the popup to show when clicked as with standard comboboxes, but can't work out why my template is preventing this. Can anyone please help shed any light?
<ControlTemplate TargetType="ComboBox" x:Key="ComboBoxTemplate">
<Border Name="Border" BorderBrush="{DynamicResource ButtonBorder}" Background="{DynamicResource ButtonBackgroundBrush}" BorderThickness="2" CornerRadius="3"
TextBlock.FontFamily="{DynamicResource Font}" TextBlock.FontSize="{DynamicResource MainFontSize}" TextBlock.Foreground="{DynamicResource PlainTextColour}">
<Grid>
<Rectangle Name="Focus" Grid.ColumnSpan="2" Visibility="Hidden" Stroke="{DynamicResource FocusColor}" Margin="0" StrokeThickness="1" StrokeDashArray="2 1" SnapsToDevicePixels="True" />
<ContentPresenter Name="Content" Content="{TemplateBinding SelectedItem}" RecognizesAccessKey="True" Margin="5" VerticalAlignment="Center" HorizontalAlignment="Center" FocusVisualStyle="{x:Null}" />
<Path x:Name="Arrow" Grid.Column="1" Fill="{DynamicResource GlyphBrush}" HorizontalAlignment="Center" VerticalAlignment="Center" Data="M 0 0 L 4 4 L 8 0 Z"/>
<Popup x:Name="PART_Popup"
IsOpen="{TemplateBinding IsDropDownOpen}">
<Border x:Name="PopupBorder" Style="{DynamicResource CustomBorder}"
HorizontalAlignment="Stretch" Height="Auto"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}"
Background="{DynamicResource WindowBackground}">
<ScrollViewer x:Name="ScrollViewer" BorderThickness="0" Padding="1">
<ItemsPresenter/>
</ScrollViewer>
</Border>
</Popup>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition Width="10"/>
</Grid.ColumnDefinitions>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter TargetName="Border" Property="Background" Value="{DynamicResource MouseOverButtonBrush}"/>
<Setter TargetName="Border" Property="BorderBrush" Value="{DynamicResource MouseOverBorder}"/>
</Trigger>
<Trigger Property="IsKeyboardFocused" Value="True">
<Setter TargetName="Focus" Property="Visibility" Value="Visible"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter TargetName="Border" Property="TextBlock.Foreground" Value="{DynamicResource DisabledTextColour}"/>
<Setter TargetName="Border" Property="Background" Value="{DynamicResource DisabledButtonBackground}"/>
<Setter TargetName="Border" Property="BorderBrush" Value="{DynamicResource DiabledButtonBorder}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>

I think you need to implement in the template ToggleButton:
<ToggleButton Name="ToggleButton" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press" />
The property IsChecked responsible for showing Popup.
And use a Popup like this:
<Popup Name="Popup" Placement="Bottom" IsOpen="{TemplateBinding IsDropDownOpen}" ... />
A complete example of the style with ToggleButton:
<!-- Template for ToggleButton -->
<ControlTemplate x:Key="ComboBoxToggleButton" TargetType="ToggleButton">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="20" />
</Grid.ColumnDefinitions>
<Border x:Name="Border" Grid.ColumnSpan="2" CornerRadius="0" Background="#A6A6A6" BorderBrush="Gray" BorderThickness="1" />
<Border Grid.Column="0" CornerRadius="0" Margin="1" Background="White" BorderBrush="Gray" BorderThickness="0" />
<Path x:Name="Arrow" Grid.Column="1" Fill="White" HorizontalAlignment="Center" VerticalAlignment="Center" Data="M 0 0 L 4 4 L 8 0 Z"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsMouseOver" Value="True">
<Setter TargetName="Border" Property="Background" Value="Black" />
<Setter TargetName="Border" Property="Cursor" Value="Arrow" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="True">
<Setter TargetName="Border" Property="Background" Value="#D0D0D0" />
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter TargetName="Border" Property="Background" Value="{StaticResource DisabledBackgroundBrush}" />
<Setter TargetName="Border" Property="BorderBrush" Value="{StaticResource DisabledBorderBrush}" />
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
<Setter TargetName="Arrow" Property="Fill" Value="{StaticResource DisabledForegroundBrush}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<!-- Template for TextBox (in ComboBox) -->
<ControlTemplate x:Key="ComboBoxTextBox" TargetType="TextBox">
<Border x:Name="PART_ContentHost" Focusable="False" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" />
</ControlTemplate>
<!-- Main style for ComboBox -->
<Style x:Key="{x:Type ComboBox}" TargetType="ComboBox">
<Setter Property="SnapsToDevicePixels" Value="True" />
<Setter Property="OverridesDefaultStyle" Value="True" />
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
<Setter Property="ScrollViewer.CanContentScroll" Value="True" />
<Setter Property="MinWidth" Value="10" />
<Setter Property="MinHeight" Value="10" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<ToggleButton Name="ToggleButton" Template="{StaticResource ComboBoxToggleButton}" Grid.Column="2" Focusable="False" IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press" />
<ContentPresenter Name="ContentSite" IsHitTestVisible="False" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" Margin="3,3,23,3" VerticalAlignment="Center" HorizontalAlignment="Left" />
<TextBox x:Name="PART_EditableTextBox" Style="{x:Null}" Template="{StaticResource ComboBoxTextBox}" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="3,3,23,3" Focusable="True" Background="Transparent" Visibility="Hidden" IsReadOnly="{TemplateBinding IsReadOnly}" />
<Popup Name="Popup" Placement="Bottom" IsOpen="{TemplateBinding IsDropDownOpen}" AllowsTransparency="True" Focusable="False" PopupAnimation="Slide">
<Grid Name="DropDown" SnapsToDevicePixels="True" MinWidth="{TemplateBinding ActualWidth}" MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border x:Name="DropDownBorder" Background="White" BorderThickness="1" BorderBrush="Gray" />
<ScrollViewer Margin="2" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="False">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95" />
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}" />
</Trigger>
<Trigger Property="IsGrouping" Value="True">
<Setter Property="ScrollViewer.CanContentScroll" Value="False" />
</Trigger>
<Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="True">
<Setter TargetName="DropDownBorder" Property="CornerRadius" Value="0" />
<Setter TargetName="DropDownBorder" Property="Margin" Value="0" />
</Trigger>
<Trigger Property="IsEditable" Value="True">
<Setter Property="IsTabStop" Value="False" />
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible" />
<Setter TargetName="ContentSite" Property="Visibility" Value="Hidden" />
<Setter Property="Cursor" Value="IBeam" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Output