Width of child control should match width of parent container - wpf

Question

I'm pretty new to WPF. I often find my self struggling with getting a bunch of child controls combined width to match a given parent container.. As in the following:
<ListBox x:Name="BrugereListBox" Grid.Column="0" Grid.Row="3" DataContext="{DynamicResource Brugere}"
ItemsSource="{Binding}"
PreviewMouseLeftButtonDown="BrugereListBox_MouseLeftButtonDown"
PreviewMouseMove="BrugereListBox_PreviewMouseMove"
>
<ListBox.ItemTemplate >
<DataTemplate >
<Border BorderBrush="Black" BorderThickness="1" Margin="2">
<StackPanel Orientation="Vertical" IsEnabled="True"
PreviewMouseLeftButtonDown="StackPanel_PreviewMouseLeftButtonDown">
<StackPanel Orientation="Horizontal" >
<Label>Navn</Label>
<TextBox Text="{Binding Name}"></TextBox>
</StackPanel>
<StackPanel Orientation="Horizontal">
<Label>Password</Label>
<TextBox Text="{Binding Password}"></TextBox>
</StackPanel>
<StackPanel Orientation="Horizontal">
<Label>Email</Label>
<TextBox Text="{Binding Email}"></TextBox>
</StackPanel>
</StackPanel>
</Border>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
In this case I'm interested in getting the width of the children of the stackpanel:
<StackPanel Orientation="Horizontal" >
<Label>Navn</Label>
<TextBox Text="{Binding Name}"></TextBox>
</StackPanel>
to match the width of
<ListBox x:Name="BrugereListBox"
Any generic solution to scenarios like this?

Answer 1

turns out to be a dupe of:
wpf border control to span the width of listboxItem
and the answer given there:
This is probably more to do with the
ListBoxItems themselves not taking up
the full width of the ListBox. Add the
HorizontalContentAlignment="Stretch"
attribute to your ListBox and see if
it stretches the individual items to
fill the width.
so change to:
<ListBox x:Name="BrugereListBox" Grid.Column="0" Grid.Row="3" DataContext="{DynamicResource Brugere}"
ItemsSource="{Binding}"
PreviewMouseLeftButtonDown="BrugereListBox_MouseLeftButtonDown"
PreviewMouseMove="BrugereListBox_PreviewMouseMove"
HorizontalContentAlignment="Stretch"
>
but as Kent says, using a Grid would be better in my opinion.

Answer 2

Use the right panel and you'll be fine. StackPanel makes its own decisions about its width/height depending on its orientation and its children. Use a Grid and it will just take up the space it is given - no more, no less.