Odd Scrollbar behaviour in WPF control - wpf

Question

I have made the following simple control, which I add to another window as a popup (starts hidden, gets changed to visible on a button click)
<UserControl x:Class="AddGroupsCtrl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:ASManager2017"
mc:Ignorable="d" d:DesignWidth="255" Height="413">
<GroupBox x:Name="groupBox" Header=" Active Directory Groups" HorizontalAlignment="Stretch" Margin="0,0,0,0" VerticalAlignment="Stretch" Height="350" Width="233" BorderBrush="{DynamicResource {x:Static SystemColors.ActiveBorderBrushKey}}">
<Grid Height="auto">
<ListBox x:Name="grouplistBox" HorizontalAlignment="Stretch" Height="auto" Margin="0,0,0,0" VerticalAlignment="Stretch" Width="auto" SelectionMode="Extended" ScrollViewer.VerticalScrollBarVisibility="Visible" Background="{DynamicResource fadeBrush}"/>
<Button x:Name="addButton" Content="Add" HorizontalAlignment="Right" Margin="0,0,22,0" VerticalAlignment="Bottom" Width="75"/>
<Button x:Name="button" Content="X" HorizontalAlignment="Right" Margin="0,0,22,0" VerticalAlignment="Top" Width="20" Height="20" Background="{DynamicResource {x:Static SystemColors.ControlLightLightBrushKey}}"/>
</Grid>
</GroupBox>
In the code behind this I have the following fragment....
For Each grp As String In gsList
grouplistBox.Items.Add(grp)
Next
Everything seems to work fine, apart from the scroll bar at the side of the listbox. This starts at about half the height of the entire control, and when trying to slide it down the list doesn't scroll, but the scroller shrinks in size until it gets to a small bar, and then starts scrolling to contents of the window. Likewise dragging the bar back up: the listbox will get to the top of the list when the bar is about halfway up the scroll-area, and then the bar will expand.
Can anyone help me correct this behaviour/explain what I am doing wrong?
Thanks.
Pete.
After more experimenting, things are getting weirder....
Imports AshbyTools
Imports System.DirectoryServices.AccountManagement
Imports System.ComponentModel
Public Class AddGroupsCtrl
Dim _domainString As String
Dim _ouString As String
Public Event addClicked(ByVal glist As List(Of String))
<Description("ouString"), DisplayName("OU String"), Category("Data")>
Public Property ouString As String
Get
Return _ouString
End Get
Set(value As String)
_ouString = value
End Set
End Property
<Description("domainString"), DisplayName("Domain String"), Category("Data")>
Public Property domainString As String
Get
Return _domainString
End Get
Set(value As String)
_domainString = value
End Set
End Property
Private Sub button_Click(sender As Object, e As RoutedEventArgs) Handles button.Click
Me.Visibility = Visibility.Hidden
End Sub
Public Sub loadGroups()
grouplistBox.Items.Clear()
Dim groupCTX As PrincipalContext = ADTools.getConnection(domainString, ouString)
Dim gList As List(Of GroupPrincipal) = ADTools.getManagedGroups(groupCTX)
Dim gsList As New List(Of String)
For Each grp As GroupPrincipal In gList
If Not (grp.DistinguishedName.Contains("Staff Groups") Or grp.DistinguishedName.Contains("Subject Groups") Or grp.DistinguishedName.Contains("Tutor Groups")) Then
gsList.Add(grp.DisplayName)
End If
Next
'For n As Integer = 1 To 70
' grouplistBox.Items.Add("item" & n)
'Next
gsList.Sort()
For Each grp As String In gsList
grouplistBox.Items.Add(grp)
Next
End Sub
Private Sub addButton_Click(sender As Object, e As RoutedEventArgs) Handles addButton.Click
Dim ret As New List(Of String)
For Each grp In grouplistBox.SelectedItems
ret.Add(grp.ToString)
Next
RaiseEvent addClicked(ret)
End Sub
End Class
Upon loadGroups() if I replace the
For Each grp As String In gsList
grouplistBox.Items.Add(grp)
Next
with the commented out code, the scrollbar works perfectly.
With the list of strings from gsList, I get the odd behaviour.
I could post the entire project, but since it is hard-coded for our active directory structure it wouldn't compile on another system. (also, as I am just using this to learn WPF and it's an internal tool, I've hard-coded numerous passwords)

Answer 1

Ok, I have solved the issue. And the answer is even more confusing. Turns out that in the code, where I got the DisplayName of the group to add to the list of string, it was returning 'Nothing' for each of them. Yet somehow displayed the list correctly (although with a screwy scrollbar). Now I have changed it to return grp.name rather than displayname, and EVERYTHING works as I'd expect.