mój kod strony .xaml:

<phone:PhoneApplicationPage
    x:Class="MVVM1Test.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:converter="clr-namespace:MVVM1Test.Resources.Converters"
    mc:Ignorable="d"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">

    <phone:PhoneApplicationPage.Resources>
        <converter:NotConverter x:Name="not"></converter:NotConverter>
    </phone:PhoneApplicationPage.Resources>

    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="LayoutRoot" Background="Gray">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
    </Grid>

</phone:PhoneApplicationPage>

notconverter.cs

namespace MVVM1Test.Resources.Converters
{
    public class NotConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return !(bool)value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return !(bool)value;
        }
    }
}

to pokazuje błąd

„nazwa NotConverter nie istnieje w przestrzeni nazw clr-namespace: MVVM1Test.Resources.Converters”

Ale dodałem również klasę konwertera do rozwiązania.