Scrolling of a listbox inside another listbox - wpf

Question

I have a listbox (with normal vertical orientation), each element of which is a listbox with horizontal orientation.
I want to have a ScrollBar inside of internal listbox. So, my problem is how to set width of internal listbox according to real current width of external.
My current code is:
<Window.Resources>
<HierarchicalDataTemplate x:Key="ItemTemplateSchedule">
<ListBox>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBoxItem>My-Very-Long-Item-Nimber-1___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-2___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-3___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-4___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-5___</ListBoxItem>
</ListBox>
</HierarchicalDataTemplate>
</Window.Resources>
<Grid>
<ListBox ItemTemplate="{StaticResource ItemTemplateSchedule}" >
>
</ListBox>
</Grid>
Current screenshot:
.
UPD1
Ok, answer to my question is setting of width for internal listbox, thanks to #sa_ddam213:
Width="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ListBox}, Path=ActualWidth}"
Now I want add some new control in each row of external listbox:
<HierarchicalDataTemplate x:Key="ItemTemplateSchedule">
<StackPanel Orientation="Horizontal" Width="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ListBox}, Path=ActualWidth}">
<TextBlock Text="This is Text in a TextBlock"/>
<ListBox >
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBoxItem>My-Very-Long-Item-Number-1___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Number-2___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Number-3___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Number-4___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Number-5___</ListBoxItem>
</ListBox>
</StackPanel>
</HierarchicalDataTemplate>
And it doesn't work now! Is it possible to solve this problem? Current screenshot:

Answer 1

You can use a FindAncestor to bind to the parent ListBox ActualWidth
Example:
<Window.Resources>
<HierarchicalDataTemplate x:Key="ItemTemplateSchedule">
<ListBox Width="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ListBox}, Path=ActualWidth}" >
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBoxItem>My-Very-Long-Item-Nimber-1___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-2___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-3___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-4___</ListBoxItem>
<ListBoxItem>My-Very-Long-Item-Nimber-5___</ListBoxItem>
</ListBox>
</HierarchicalDataTemplate>
</Window.Resources>
Result: