App does not start - ViewModel problem?

Hey there. I found some example Code for ViewModel which does not work for me. My problem is that when I start the app it is about to launch and then just closes itself. I get no errors from Visual Studio besides the notification that there is something wrong with XamarinFormsPrevieweriOS.

This is my Code:

SimpleMultiplierViewModel.cs:

namespace BookCodedotNet2
{
    class SimpleMultiplierViewModel : INotifyPropertyChanged
    {
        double multiplicand, multiplier, product;

        public event PropertyChangedEventHandler PropertyChanged;

        public double Multiplicand
        {
            set
            {
                if (multiplicand != value)
                {
                    multiplicand = value;
                    OnPropertyChanged("Multiplicand");
                    UpdateProduct();
                }
            }

            get
            {
                return Multiplicand;
            }
        }

        public double Multiplier
        {
            set
            {
                if (multiplier != value)
                {
                    multiplier = value;
                    OnPropertyChanged("Multiplier");
                    UpdateProduct();
                }
            }

            get
            {
                return multiplier;
            }
        }

        public double Product
        {
            protected set
            {
                if (product != value)
                {
                    product = value;
                    OnPropertyChanged("Product");
                }
            }

            get
            {
                return product;
            }
        }

        void UpdateProduct()
        {
            Product = Multiplicand * Multiplier;
        }

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if(handler != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        public SimpleMultiplierViewModel()
        {
        }
    }
} 

SimpleMultiplierPage.xaml:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="BookCodedotNet2.SimpleMultiplierPage"
             xmlns:local="clr-namespace:BookCodedotNet2"
             Padding="10,0">

    <ContentPage.Resources>
        <ResourceDictionary>
            <local:SimpleMultiplierViewModel x:Key="viewModel"/>

            <Style TargetType="Label">
                <Setter Property="FontSize" Value="Large"/>
            </Style>
        </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout BindingContext="{StaticResource viewModel}">
        <StackLayout VerticalOptions="CenterAndExpand">
            <Slider Value="{Binding Multiplicand}"/>
            <Slider Value="{Binding Multiplier}"/>
        </StackLayout>

        <StackLayout Orientation="Horizontal"
                     Spacing="0"
                     VerticalOptions="CenterAndExpand"
                     HorizontalOptions="Center">
            <Label Text="{Binding Multiplicand, StringFormat='{0:F3}'}"/>
            <Label Text="{Binding Multiplier, StringFormat=' x {0:F3}'}"/>
            <Label Text="{Binding Product, StringFormat=' = {0:F3}'}"/>
        </StackLayout>
    </StackLayout>

</ContentPage>