WPF Combobox: Autocomplete

Question

Hi, I have implemented a Autocomplete enabled Combobox in WPF. It is like below...

    private void cbxSession_Loaded(object sender, RoutedEventArgs e)
{
    cbxSession.ApplyTemplate();

    TextBox textBox = cbxSession.Template.FindName("PART_EditableTextBox", cbxSession) as TextBox;
    textBox.IsReadOnly = false;
    if (textBox != null)
    {
        textBox.KeyUp += new KeyEventHandler(textBox_KeyUp);
        textBox.KeyUp += delegate
        {
            ///open the drop down and start filtering based on what the user types into the combobox
            cbxSession.IsDropDownOpen = true;
            cbxSession.Items.Filter += a =>
            {
                if (a.ToString().ToUpper().Contains(textBox.Text.ToUpper()))
                    return true;
                else
                    return false;
            };
        };
    }

}

void textBox_KeyUp(object sender, KeyEventArgs e)
{
    if ((e.Key == System.Windows.Input.Key.Up) || (e.Key == System.Windows.Input.Key.Down))
    {
        e.Handled = true;
    }
    else if (e.Key == System.Windows.Input.Key.Enter)
    {
        e.Handled = true;
        cbxSession.IsDropDownOpen = false;
    }
}

void textBox_KeyDown(object sender, KeyEventArgs e)
{
    cbxSession.SelectionChanged -= cbxSession_SelectionChanged;
    if (e.Key == System.Windows.Input.Key.Enter)
    {
        e.Handled = true;
        cbxSession.SelectionChanged += cbxSession_SelectionChanged;
    }
    if ((e.Key == System.Windows.Input.Key.Up) || (e.Key == System.Windows.Input.Key.Down))
    {
        e.Handled = true;
    }

}

private void cbxSession_DropDownClosed(object sender, EventArgs e)
{
    if (cbxSession.Text != "")
    {
        TextBox textBox = cbxSession.Template.FindName("PART_EditableTextBox", cbxSession) as TextBox;
        if (!cbxSession.Items.Contains(textBox.Text))
        {
            textBox.Text = cbxSession.Text;
        }
    }

}

private void cbxSession_DropDownOpened(object sender, EventArgs e)
{
    cbxSession.Items.Filter += a =>
    {
        return true;
    };
}



 <ComboBox x:Name="cbxSession" Width="260" Canvas.Top="5" Canvas.Left="79" Height="25" Visibility="Visible" SelectionChanged="cbxSession_SelectionChanged" MaxDropDownHeight="200" IsTextSearchEnabled="False" IsEditable="True" IsReadOnly="True" Loaded="cbxSession_Loaded" DropDownClosed="cbxSession_DropDownClosed" StaysOpenOnEdit="True" DropDownOpened="cbxSession_DropDownOpened">
  <ComboBox.ItemsPanel>
   <ItemsPanelTemplate>
    <VirtualizingStackPanel IsVirtualizing="True" IsItemsHost="True"/>
   </ItemsPanelTemplate>
  </ComboBox.ItemsPanel>
 </ComboBox>

1. But, the problem I am facing is... When I try searching, the first character goes missing.

And this happens only once.

1. Secondly, When I am using Arrow buttons to the filtered items, the ComboboxSelectionChanged event is fired. Is there any way to make it fire only on the click of 'Enter'