Come aggiungere l'opzione "Tutti" a una casella combinata in WPF con associazione dal database

Question

Ho il seguente ComboBox in WPF. So che posso aggiungere l'opzione ALL con CompositeCollection, ma non so come. Sarebbe bello se qualcuno mi aiutasse con un breve tutorial.

<ComboBox SelectionChanged="ComboBoxOperatingPoints_SelectionChanged" 
      x:Name="ComboBoxOperatingPoints" 
      DropDownOpened="ComboBoxOperatingPoints_DropDownOpened_1" 
      FontSize="30" 
      HorizontalAlignment="Right" 
      Margin="40,40,0,0" 
      VerticalAlignment="Top" 
      Width="200" 
      Height="50" 
      IsSynchronizedWithCurrentItem="True" 
      ItemsSource="{Binding OperatingPoints}" 
      DisplayMemberPath="name" 
      SelectedValue="{Binding OperatingPointID,UpdateSourceTrigger=PropertyChanged,TargetNullValue=''}" 
      SelectedValuePath="operating_point_id"> 
</ComboBox> 

Answer 1

Prova questo (msdn):

<ComboBox x:Name="ComboBoxOperatingPoints" 
      SelectionChanged="ComboBoxOperatingPoints_SelectionChanged" 
      Width="200" Height="50" 
      IsSynchronizedWithCurrentItem="True" 
      DisplayMemberPath="name"   
      SelectedValuePath="operating_point_id"> 
    <ComboBox.Resources> 
     <CollectionViewSource x:Key="comboBoxSource" Source="{Binding Path=OperatingPoints}" /> 
    </ComboBox.Resources> 
    <ComboBox.ItemsSource> 
     <CompositeCollection> 
      <local:OpPoint name="all" operating_point_id="-1" /> 
      <CollectionContainer Collection="{Binding Source={StaticResource comboBoxSource}}" /> 
     </CompositeCollection> 
    </ComboBox.ItemsSource> 
</ComboBox>