TabControl.VerticalAlignment = Stretch doesn't do anything

Question

I am trying to make a TabControl to auto resize according to the its outer space(it's in a StackPanel):

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Height="100">
    <Grid>
        <StackPanel>
            <TabControl 
                BorderBrush="Red" 
                BorderThickness="2" 
                VerticalAlignment="Stretch" 
                VerticalContentAlignment="Stretch">

                <TabItem Header="Tab1"/>
                <TabItem Header="Tab2"/>
            </TabControl>
        </StackPanel>
    </Grid>
</Window>

The snippet above produces the following window, whilst I want the red border to reach the bottom of the window:

Answer 1

The problem is your StackPanel. StackPanels won't stretch their children.

Instead, use a DockPanel: The last child will be stretched to fill the remaining space (see LastChildFill, which defaults to true).

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Height="100">
    <Grid>
        <DockPanel>
            <TabControl BorderBrush="Red" BorderThickness="2">
                <TabItem Header="Tab1"/>
                <TabItem Header="Tab2"/>
            </TabControl>
        </DockPanel>
    </Grid>
</Window>

Explicitly setting VerticalAlignment is not necessary, since its default value is already Stretch.

Related Link: Panels Overview on MSDN

Answer 2

You can bind the height to parent window's actual height.

<TabControl 
    BorderBrush="Red" 
    BorderThickness="2"
    Height="{Binding Path=ActualHeight,
         RelativeSource={RelativeSource Mode=FindAncestor,
            AncestorType={x:Type Window}}}">
    <TabItem Header="Tab1"/>
    <TabItem Header="Tab2"/>
</TabControl>