<UserControl x:Class="SilverlightApplication9.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <Grid x:Name="LayoutRoot" Background="White">
        <sdk:TabControl Height="234" HorizontalAlignment="Left" Margin="52,44,0,0" Name="tabControl1" VerticalAlignment="Top" Width="326">
            <sdk:TabItem Header="tabItem1" Name="tabItem1">
                <Grid>
                    <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="74,44,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
                </Grid>
            </sdk:TabItem>
            <sdk:TabItem Header="tabItem2" Name="tabItem2">
                <Grid>
                    <sdk:DataGrid ItemsSource="{Binding strs}" RowBackground="White" AutoGenerateColumns="False" Height="141" HorizontalAlignment="Left" Margin="36,12,0,0" Name="dataGrid1" VerticalAlignment="Top" Width="199">
                        <sdk:DataGrid.Columns>
                            <sdk:DataGridTextColumn Binding="{Binding}" CanUserReorder="True" CanUserResize="True" CanUserSort="True" Width="Auto" />
                        </sdk:DataGrid.Columns>
                    </sdk:DataGrid>
                </Grid>
            </sdk:TabItem>
        </sdk:TabControl>
    </Grid>
</UserControl>

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Collections.ObjectModel;

namespace SilverlightApplication9
{
    public partial class MainPage : UserControl
    {
        private ObservableCollection<string> _strs = new ObservableCollection<string>();
        public ObservableCollection<string> strs { get { return _strs; } set { _strs = value; } }
        public MainPage()
        {
            this.DataContext = this;
            InitializeComponent();
            strs.Add("1");
            strs.Add("2");
            strs.Add("3");
            strs.Add("4");
            strs.Add("5");
        }
        private void button1_Click(object sender, RoutedEventArgs e)
        {
            dataGrid1.SelectedIndex = 2;
        }
    }

}