How to make the StackPanel or DockPanel stretch to fit their containers in WPF?

Question

I have a Grid as a root container with two columns defined (There\'s only one row).
The first column has flexible width and second column has 300px fixed width.

Answer 1

You can make the Content of every ListBoxItem stretch by setting HorizontalContentAlignment in the ItemContainerStyle

<ListBox ...>
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
        </Style>
    </ListBox.ItemContainerStyle>