Polling active directory, Trying to update UI each time - wpf

Question

My interface displays a list of AD users, and a pair of buttons next to each name to disable/enable that user. Each button is bound to an appropriate DelegateCommand. Clicking the 'enable' button disables that button and enables the other one. Users could be getting enabled/disabled by other means by other users, and I'd like this to be reflected in my app.
What I've tried:
RaisePropertyChangedEvent("CommandEnable");
RaisePropertyChangedEvent("CommandDisable");
I'm using a MVVM.
I've got a Dispatch timer set to trigger the above lines every second.
EDIT: I seem to have solved this issue by updating the whole user list, and re-assigning it as the ItemSource for my ListBox.
I can't help but feel this is messy. Is there a way to only trigger an update for the users for which their enabled property has changed? In my Model
public class UserItem //The model
{
private UserPrincipal _User;
public string SamAccountName {
get
{
return _User.SamAccountName;
}
}
public UserItem(UserPrincipal user)
{
_User = user;
}
public bool Enabled
{
get
{
if (_User.Enabled != null)
{
return (bool)_User.Enabled;
} else
{
return false;
}
}
set
{
_User.Enabled = value;
_User.Save();
}
}
}
And in my ViewModel:
public class UserVM : ObservableObject, IComparable //ViewModel
{
private UserItem _userItem;
private ISet<String> _Groups = new HashSet<String>();
public string SamAccountName
{
get
{
return _userItem.SamAccountName;
}
}
public UserVM(UserPrincipal user, ISet<String> groups)
{
_userItem = new UserItem(user);
_Groups = groups;
}
public bool IsInGroup(String groupName)
{
return (_Groups.Contains(groupName)) ? true : false;
}
public bool Enabled
{
get
{
return _userItem.Enabled;
}
set
{
_userItem.Enabled = value;
RaisePropertyChangedEvent("Enabled");
RaisePropertyChangedEvent("CommandEnable");
RaisePropertyChangedEvent("CommandDisable");
}
}
private void EnableUser(object state)
{
Enabled = true;
}
private bool CanEnable(object state)
{
return !Enabled;
}
private void DisableUser(object state)
{
Enabled = false;
}
private bool CanDisable(object state)
{
return Enabled;
}
public int CompareTo(object comp)
{
return this._userItem.SamAccountName.CompareTo(((UserVM)comp).SamAccountName);
}
public ICommand CommandEnable
{
get {
return new DelegateCommand(EnableUser, CanEnable);
}
}
public ICommand CommandDisable
{
get { return new DelegateCommand(DisableUser, CanDisable); }
}
}
My XML:
<Window x:Class="Toggle.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Toggle"
mc:Ignorable="d"
Title="MainWindow" Height="512" Width="339">
<Window.Resources>
</Window.Resources>
<Grid Margin="10">
<ListBox Name="lbUserList" HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch" Margin="0,22,0,0">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid Margin="0,2">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="50"/>
<ColumnDefinition Width="50"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding SamAccountName}" />
<Button Name="btnEnable" Grid.Column="1" Content="Enable" Background="Green" Command="{Binding CommandEnable}"/>
<Button Name="btnDisable" Grid.Column="2" Content="Disable" Background="Red" Command="{Binding CommandDisable}"/>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<ComboBox Name="cbGroupList" SelectedIndex="0" DropDownClosed="ComboBox_DropDownClosed" HorizontalAlignment="Stretch" VerticalAlignment="Top" Width="Auto"/>
</Grid>
</Window>
Also, this polling is interfering with the user clicking of the button. If the UI update happens at the exact same time that the user clicks the button, the button click doesn't register. My gut tells me that this is a non-resolvable race condition (user-writer conflict), but I'm hopeful that I am wrong.