<Window x:Class="MainWindow"
 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 Title="MainWindow" Height="350" Width="525">
  <StackPanel>
    <ComboBox
        Name="cmbTest"
        IsEditable="True"
        SelectionChanged="ComboBox_SelectionChanged">
    </ComboBox>
  </StackPanel>
</Window>