How to get a ListBox ItemTemplate to stretch horizontally the full width of the ListBox?

I found another solution here, since I ran into both post...

This is from the Myles answer:

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

This worked for me.

I'm sure this is a duplicate, but I can't find a question with the same answer.

Add HorizontalContentAlignment="Stretch" to your ListBox. That should do the trick. Just be careful with auto-complete because it is so easy to get HorizontalAlignment by mistake.

If your items are wider than the ListBox, the other answers here won't help: the items in the ItemTemplate remain wider than the ListBox.

The fix that worked for me was to disable the horizontal scrollbar, which, apparently, also tells the container of all those items to remain only as wide as the list box.

Hence the combined fix to get ListBox items that are as wide as the list box, whether they are smaller and need stretching, or wider and need wrapping, is as follows:

<ListBox HorizontalContentAlignment="Stretch" 
         ScrollViewer.HorizontalScrollBarVisibility="Disabled">

(credits for the scroll bar idea)