Data binding into textblock from sqlite database on windows store app

I'm trying to bind my data from sqlite.net database into textblock. I've searched a lot about it, but I still have a few problems: 1) anoying exception occurs where in the Additional Information is: "Constraint" and nothing else. The problem is also that it doesn't appear every time I run the app. 2) I cannot see my Binding data into the textblock.

I've composed me code according to this example: Windows Store App writing sqlite query into the listview's textblocks

I've tried also this select data from sqlite database and binding values to listbox item in windows phone 8 apps but none of this solving my problem.

Here is my XAML code:

    <Grid>
    <Grid.Background>
        <ImageBrush ImageSource="/Assets/rankingTlo.png"/>
    </Grid.Background>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="1*"/>
        <ColumnDefinition Width="5*"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="1*"/>
        <RowDefinition Height="4*"/>
    </Grid.RowDefinitions>
    <TextBlock Grid.Column="1" HorizontalAlignment="Center"  Text="Pytanie" VerticalAlignment="Top" FontFamily="Arial" FontSize="20" Margin="-83,71,0,0" Foreground="#FF353535" FontWeight="Bold"/>
    <TextBlock Grid.Column="1" HorizontalAlignment="Center" Text="2" VerticalAlignment="Top" Foreground="#FFB41019" Margin="17,59,0,0" FontFamily="Arial" FontWeight="Bold" FontSize="33" />
    <TextBlock Grid.Column="1" HorizontalAlignment="Center" Text="z" VerticalAlignment="Top" Foreground="#FF353535" Margin="56,71,0,0" FontFamily="Arial" FontWeight="Bold" FontSize="20" />
    <TextBlock Grid.Column="1" HorizontalAlignment="Center" Text="14" VerticalAlignment="Top" Foreground="#FF353535" Margin="109,59,0,0" FontFamily="Arial" FontWeight="Bold" FontSize="33" />
    <TextBlock Grid.Column="1" HorizontalAlignment="Center"  Text="poziom" VerticalAlignment="Top" FontFamily="Arial" FontSize="16" Margin="-88,96,0,0" Foreground="#FF353535" FontWeight="Bold"/>
    <TextBlock Grid.Column="1" HorizontalAlignment="Center"  Text="licealista" VerticalAlignment="Top" FontFamily="Arial" FontSize="16" Margin="47,96,0,0" Foreground="#FFB41019" FontWeight="Bold"/>

    <ListView Name="listView1" Grid.Column="1" Grid.Row="1" >
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextBlock Width="Auto" Height="50" HorizontalAlignment="Left" TextWrapping="Wrap" Text="{Binding tresc_pytania}" VerticalAlignment="Top" Foreground="Black" FontFamily="Arial" FontSize="24"/>                   
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

class pytania
{
    [PrimaryKey]
    public int id_pytania { get; set; }
    public string tresc_pytania { get; set; }
    public int poziom_trudnosci { get; set; }        
    public string odpowiedz1 { get; set; }
    public string odpowiedz2 { get; set; }
    public string odpowiedz3 { get; set; }
    public string odpowiedz4 { get; set; }
    public int dobra_odpowiedz { get; set; }

}

    private void Page_Loaded(object sender, RoutedEventArgs e)
    {
        string dbPath = Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path, "baza.ext");

        using (var dbConn = new SQLite.SQLiteConnection(dbPath))
        {
            var query = dbConn.Table<pytania>();
            listView1.ItemsSource = query.ToList();
        }
    }

Hope to hear from you some piece of advice. Best regards, Tomas