Question

The right-aligned label doesn’t reach the right border:

<StackPanel Orientation="Horizontal" HorizontalAlignment="Stretch">
    <Label Content="Left Align" HorizontalAlignment="Left"/>
    <Label Content="Right Align" HorizontalAlignment="Right" />
</StackPanel>

It seems that both labels don’t take up full available width even though I’ve specified HorizontalAlignment=”Stretch” . What is the cause of it?

Answer 1

You should use a DockPanel instead of a StackPanel for that.

See also Align items in a stack panel? or

<DockPanel LastChildFill="False">
    <Label Content="Left Align" DockPanel.Dock="Left"/>
    <Label Content="Right Align" DockPanel.Dock="Right" />
</DockPanel>

And @santosc described here why the alignment with StackPanel doesn’t work as you expected:

A stackpanel, no matter how you stretch it, will collapse around the
children. you can’t make it grow more than that.