Problem z prostym progremem - Visual 17

<Window x:Class="Hello.MainWindow"
        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"
        xmlns:local="clr-namespace:Hello"
        mc:Ignorable="d"
        Title="Okno startowe" Height="350" Width="525">
    <Grid>

        <TextBlock x:Name="x" HorizontalAlignment="Center" Margin="58,70,54,214" TextWrapping="Wrap" Width="405" Text="Podaj imię" FontSize="24"/>
        <TextBox x:Name="userName" HorizontalAlignment="Left" Margin="55,114,0,0" TextWrapping="Wrap" Text="userName" VerticalAlignment="Top" Height="34" Width="262" FontSize="14"/>
        <Button x:Name="ok" Content="OK" HorizontalAlignment="Left" Margin="337,110,0,0" VerticalAlignment="Top" Width="78" Height="34" Click="okClick"/>


    </Grid>
</Window>

using System.Windows;

namespace Hello
{
    /// <summary>
    /// Logika interakcji dla klasy MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void okClick(object sender, RoutedEventArgs e)
        {
            MessageDialog msg = new MessageDialog ("Hello" + userName.Text);
            msg.ShowAsync();
        }
    }
}