How to bottom align text in WPF RichTextBox - wpf

Question

How I can bottom align text in RichTextBox? It seems that control doesn't support it directly. So I am looking for ways to emulate it. Ideally I would have the boundary of the control fixed and end of text aligned with the bottom.

Answer 1

The text comes from a ScrollViewer named PART_ContentHost inside the default control template for the TextBoxBase which is wrapped by the RichTextBox. You should override the control template and either have the ScrollViewer declare its VerticalAlignment to be Bottom, or have it template bind to the VerticalContentAlignment.
Below, I've done the latter. This is a modified version of the default control template as pulled from Blend. The only change I've made is to add VerticalAlignment="{TemplateBinding VerticalAlignment}" to the ScrollViewer.
(Also note that it references Microsoft_Windows_Themes which is defined as xmlns:Microsoft_Windows_Themes="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero"
I am unsure how this will work if Aero is not on the user's machine)
<Style x:Key="BottomAlignedTextBoxBaseStyle"
TargetType="TextBoxBase"
BasedOn="{StaticResource {x:Type TextBoxBase}}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBoxBase}">
<Microsoft_Windows_Themes:ListBoxChrome x:Name="Bd"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}"
Background="{TemplateBinding Background}"
RenderMouseOver="{TemplateBinding IsMouseOver}"
RenderFocused="{TemplateBinding IsKeyboardFocusWithin}" SnapsToDevicePixels="true">
<ScrollViewer x:Name="PART_ContentHost"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}" />
</Microsoft_Windows_Themes:ListBoxChrome>
<ControlTemplate.Triggers>
<Trigger Property="IsEnabled"
Value="false">
<Setter Property="Background"
TargetName="Bd"
Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
<Setter Property="Foreground"
Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Then, to use it, simply say:
<RichTextBox Style="{StaticResource BottomAlignedTextBoxBaseStyle}"
VerticalContentAlignment="Bottom" />