private DataTable _dataSource = new DataTable( );

     
      SqlConnection connection = new SqlConnection( ConfigurationManager.ConnectionStrings[ "DSRFID_Provider" ].ConnectionString );
      SqlCommand command = new SqlCommand(
          "SELECT CAST(ROW_NUMBER() OVER(ORDER BY idn ASC ) as int) as id
            , idn, name_R, dbWtPowerEf, dbCable, dbAntenn
           from tb_Readers2"
        , connection );
      connection.Open( );
      SqlDataReader reader = command.ExecuteReader( );
      _dataSource.Load( reader );
      reader.Close( );
      connection.Close( );

       int id= (int)_dataSource.Select( "idn = " + idn.ToString( ) )[0][0];
        IdnSelected = id;
        listViewMain.SelectedIndex = IdnSelected-1;

SelectedValue=5;

<Page x:Class="DSRFID_test2.Samples_MWS.ListBox_SelectedValue"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      
      xmlns:sys="clr-namespace:System;assembly=mscorlib"
      
      mc:Ignorable="d" 
      Title="ListBox_select"
      >


    <StackPanel 
      Background="LightCyan" Margin="10,70,10,0" Height="472" VerticalAlignment="Top" Orientation="Vertical" >
      
      <!--по умолч источником данных является DataContext - этот член поэтому пропушен-->
      <ListBox Margin="15"
               ItemsSource="{Binding}"                
               SelectedValuePath="N" 
               DisplayMemberPath="Name"
               x:Name="list" 
               Padding="2"
               Background="LightCoral" Foreground="Black" />
      <!--Другие варианты-->
    <!--SelectedValuePath="Name"-->
    <!--DisplayMemberPath="Name"-->


    <TextBox Background="Yellow" Width="80" Height="30" Margin="10" 
          Text="{Binding SelectedValue, UpdateSourceTrigger=PropertyChanged, ElementName=list}" 
                 />
    <!--Text="{Binding SelectedValue, UpdateSourceTrigger=PropertyChanged, ElementName=list}"-->
    <!--Text="{Binding SelectedValue, ElementName=list}"-->

    <Label Background="Yellow" Width="80" Height="30" Margin="10" HorizontalAlignment="Left"
          Content="{Binding SelectedItem, ElementName=list}"
               />

      <Button Name="SelectedValue1" Content="SelectedValue1" Padding="5"
              HorizontalAlignment="Left" Margin="180,30,0,0" VerticalAlignment="Top" 
              Click="SelectedValue1_Click" Height="30" 
            />




      <!--=============-->
        <Label Name="a1" FontSize="12">
          <TextBlock TextWrapping="Wrap"  xml:space="preserve">
SelectedItem                   возвращает выбранный объект(типа Number),
а SelectedValue      возвращает значение SelectedValue.N (типа int).
Кроме того, каждый объект в ListBox ассоциируется со значением своего поля N.        
Задав значение SelectedValue будет выбран объект у которого свойство N равно SelectedValue,
если таких объектов окажется несколько,
в качестве SelectedItem будет установлен первый по порядку
            СМ http://kindelephant.blogspot.ru/2011/03/selectedvalue-selecteditem.html
          </TextBlock></Label>

    </StackPanel>

</Page>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace DSRFID_test2.Samples_MWS {

  public class ВшыздфнValue_and_Otherth : Page {
  }

    public partial class ListBox_SelectedValue : Page {

      //====== КЛАСС СТРАНИЦЫ ==================

    
    public ListBox_SelectedValue( ) {
      InitializeComponent( );
      //lis1.Items.Add( "line0" );
      //lis1.Items.Add( "line1" );
      //lis1.SelectedIndex = 1;
      DataContext = new Number[ ]{
        new Number(1, @"one"),  
        new Number(2, @"two"),   
        new Number(3, @"three"),   
        new Number(88, @"four"),   
        new Number(5, @"five")
      };
        

      System.Collections.ArrayList myAL = new System.Collections.ArrayList {"aa", "bbb", "cccc","ddD"};
      int i=myAL.IndexOf("cccc");

    }


    private void SelectedValue1_Click( object sender, RoutedEventArgs e ) {
      //list.SelectedIndex += 1;
      list.SelectedValue = 3;
      //list.SetValue(SelectedValue1,3)
    }
  }



  //====== КЛАСС Number ==================
  class Number {
  //class Number : System.Collections.ArrayList {


    public int N { get; set; }
    public String Name { get; set; }


    public override string ToString( ) {
      return String.Format( "{0} is {1}", N, Name );
    }


    public Number( int n, String name ) {
      N = n;
      Name = name;
    }
  }
}