Why does my TextBox with custom control template not have a visible text cursor?

Question

I have a custom control template which is set via the style property on a TextBox. The visual poperties are set correctly, even typing to the textbox works, but there is no insertion cursor (the | symbol) visible which makes editing challenging for our users.

How does the control template need changing to get the traditional TextBox behavior back?

<Style x:Key="DemandEditStyle" TargetType="TextBox">
    <EventSetter Event="LostFocus" Handler="DemandLostFocus" />
    <Setter Property="HorizontalAlignment" Value="Stretch" />
    <Setter Property="VerticalAlignment" Value="Stretch" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate>
                <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="1" />
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="*" />
                        <RowDefinition Height="1" />
                    </Grid.RowDefinitions>
                    <Grid.Background>
                        <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                            <GradientStop Color="White" Offset="0" />
                            <GradientStop Color="White" Offset="0.15" />
                            <GradientStop Color="#EEE" Offset="1" />
                        </LinearGradientBrush>
                    </Grid.Background>
                    <Border Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" Background="Black" />
                    <Border Grid.Row="0" Grid.Column="1" Grid.RowSpan="2" Background="Black" />
                    <Grid Grid.Row="0" Grid.Column="0" Margin="2">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="1" />
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="1" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="1" />
                            <RowDefinition Height="*" />
                            <RowDefinition Height="1" />
                        </Grid.RowDefinitions>
                        <Border Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3" Background="Black" />
                        <Border Grid.Row="0" Grid.Column="0" Grid.RowSpan="3" Background="Black" />
                        <Border Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="3" Background="#CCC" />
                        <Border Grid.Row="0" Grid.Column="2" Grid.RowSpan="3" Background="#CCC" />
                        <TextBlock Grid.Row="1" Grid.Column="1"
                               TextAlignment="Right" HorizontalAlignment="Center" VerticalAlignment="Center" 
                               Padding="3 0 3 0" Background="Yellow"
                               Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Text}"
                               Width="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Grid}, AncestorLevel=1}, Path=ActualWidth}" />
                    </Grid>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Update: Replacing the inner-most TextBox with a ScrollViewer and naming it PART_ContentHost indeed shows the text insertion cursor.

Answer 1

I suppose the reason is that your template lacks an element called PART_ContentElement. As stated here, an element with that name is used to display the content of the TextBox. However, in the v3.5 version of this document, the element is called PART_ContentHost and is further restricted to be a ScrollViewer or an AdornerDecorator.

Answer 2

You should base your Style on the old Style of TextBox:

<Style x:Key="DemandEditStyle" TargetType="TextBox" BasedOn="{StaticResource {x:Type TextBox}}">