WPF

System.Windows.Controls.AutoCompleteBox

<Window x:Class="auotocomplitetrial.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:toolkit="clr-  namespace:System.Windows.Controls;assembly=System.Windows.Controls.Input.Toolkit"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <toolkit:AutoCompleteBox Name="autocompleteBox"  Height="50" Width="300"
                                 ItemsSource="{Binding MyList}"
                                 IsTextCompletionEnabled="True">
        </toolkit:AutoCompleteBox>
    </Grid>
</Window>

public partial class MainWindow : Window
 {
     private List<string> myList;

     public List<string> MyList
     {
         get { return myList; }
     }

     public MainWindow()
     {
         InitializeComponent();

         myList = new List<string>
                          {
                              "Macedonia",
                              "Madagascar",
                              "Malawi",
                              "Malaysia",
                              "Maldives",
                              "Mali",
                              "Malta",
                              "Marshall Islands",
                              "Mauritania",
                              "Mauritius",
                              "Mexico",
                              "Micronesia",
                              "Moldova",
                              "Monaco",
                              "Mongolia",
                              "Montenegro",
                              "Morocco",
                              "Mozambique",
                              "Myanmar"
                          };
         //autocompleteBox.ItemsSource = myList;
     }
 }

//autocompleteBox.ItemsSource = myList;

ItemsSource="{Binding MyList}"

private void loadView(View View, _ArgsBase Args = null)
{
    ViewInfo tabInfo = new ViewInfo { View = View, EntityId = 0};

    // If the view is already open, then activate its tab
    if (TabManager.IsTabOpen(tabInfo))
    {
        TabManager.ActivateTab(tabInfo);
    }
    else
    {
        // Create an instance of the view and VM
        _DataEntryViewModelBase vm = null;
        UserControl view = null;
        string headerText = string.Empty;

        switch (View)
        {
            case View.Dashboard:
                headerText = "Dashboard";
                vm = new DashboardViewModel();
                view = new DashboardView();
                break;

            case View.JobCenter:
                headerText = "Job Center";
                vm = new JobCenterViewModel();
                view = new JobCenterView();
                break;

            case View.CompanyCenter:
                headerText = "Company Center";
                vm = new CompanyCenterViewModel();
                view = new CompanyCenterView();
                break;

            case View.MaterialsCenter:
                headerText = "Materials Center";
                vm = new MaterialsCenterViewModel();
                view = new MaterialsCenterView();
                break;
        }

        if (vm == null)
        {
            return;
        }

        // Load the vm's data and assign it to the view
        vm.Load(Args);
        view.DataContext = vm;

        // Cretae a tab and assign the view to it
        TabItem tabItem = new TabItem();

        tabItem.Header = headerText;
        tabItem.Content = view;
        tabItem.Tag = tabInfo;

        // Add the tab and activate it
        TabManager.AddTab(tabItem);
    }
}

    internal void ExpandAll(TreeViewItem tvi)
    {
        if (tvi.IsExpanded)
        {
            for (int nIndex = 0; nIndex < tvi.Items.Count; nIndex++)
            {
                TreeViewItem tviCurrent = tvi.ItemContainerGenerator.ContainerFromIndex(nIndex) as TreeViewItem;

                if ((object)tviCurrent != null)
                    ExpandAll(tviCurrent);
            }
        }
        else
        {
            if (tvi.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
            {
                EventHandler handler = null;

                handler = new EventHandler(delegate
                {
                    if (tvi.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
                    {
// ONLY GETS IN HERE ONCE                       tvi.ItemContainerGenerator.StatusChanged -= handler;
                        ExpandAll(tvi);
                    }
                });

                tvi.ItemContainerGenerator.StatusChanged += handler;
            }

            tvi.SetCurrentValue(TreeViewItem.IsExpandedProperty, true);
        }
    }