<ComboBox Canvas.Left="92" Canvas.Top="150"
		x:Name="MyComboBox" 
		Header="My Combo Box" 
	></ComboBox>

	//----- SET UP COMBO BOXES -----
	MyComboBox.Items.Clear();
	MyComboBox.Items.Add("A");
	MyComboBox.Items.Add("B");
	MyComboBox.Items.Add("C");
	MyComboBox.SelectedIndex = 0;

Styled Example

  <ComboBox Canvas.Left="92" Canvas.Top="150" x:Name="MyComboBox" Style="{StaticResource cmbSetupRelays}" />

In App.xaml

        <!-- COMBO BOX SETUP RELAYS -->
        <Style x:Key="cmbSetupRelays" TargetType="ComboBox">
            <Setter Property="Width" Value="178" />
            <Setter Property="Height" Value="28" />
            <Setter Property="Background" Value="LightGray" />
            <Setter Property="Foreground" Value="#460000"/>
            <Setter Property="BorderBrush" Value="{ThemeResource SystemControlForegroundTransparentBrush}" />
            <Setter Property="BorderThickness" Value="{ThemeResource ButtonBorderThemeThickness}" />
            <Setter Property="Padding" Value="0,0,0,0" />
            <Setter Property="HorizontalAlignment" Value="Center" />
            <Setter Property="VerticalAlignment" Value="Center" />
            <Setter Property="FontFamily" Value="Arial" />
            <Setter Property="FontWeight" Value="Bold" />
            <Setter Property="FontSize" Value="13" />
            <Setter Property="UseSystemFocusVisuals" Value="True" />
        </Style>

Function call

<ComboBox Canvas.Left="92" Canvas.Top="150" x:Name="MyComboBox" SelectionChanged="EditComboBox_SelectionChanged" />

	private async void EditComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
	{
		try
		{
			//Get combobox name
			var PageObject = sender as ComboBox;

			// = PageObject.SelectedIndex;

		}
		catch (Exception ex)
		{
			System.Diagnostics.Debug.WriteLine("Exception: " + ex.Message);
		}
	}