You can set HorizontalAlignment
to Left, set your MaxWidth
and then bind Width
to the ActualWidth
of the parent element:
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<StackPanel Name="Container">
<TextBox Background="Azure"
Width="{Binding ElementName=Container,Path=ActualWidth}"
Text="Hello" HorizontalAlignment="Left" MaxWidth="200" />
</StackPanel>
</Page>