Navigation MVVM whit IocContainers and INotifyPropertyChanged

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C#

MVVM

I'll made an universal Windows 10 application with MVVM. But now I will navigate from ShowWeatherPage to ShowWeatherDetailPage when I click on an item. I will give that item to that new page. The problem is now, when I raise the PropertyChangedEventHandler from the ApplicationViewModel, is this null. How comes that?


Based on this question on Stack Overflow, I have made this code:

IocContainer

public class IocContainer
{
    static IocContainer()
    {
        SimpleIoc.Default.Register<ApplicationViewModel>(false);
        SimpleIoc.Default.Register<ShowWeatherViewModel>(false);
        SimpleIoc.Default.Register<ShowWeatherPage>(false);
        SimpleIoc.Default.Register<ShowWeatherDetailPage>(false);
        SimpleIoc.Default.Register<ShowWeatherDetailViewModel>(false);
    }

    public static IocContainer Ioc
    {
        get { return App.Current.Resources["ioc"] as IocContainer; }
    }

    public ShowWeatherPage ShowWeatherPage
    {
        get { return SimpleIoc.Default.GetInstance<ShowWeatherPage>(); }
    }

    public ShowWeatherViewModel ShowWeatherViewModel
    {
        get { return SimpleIoc.Default.GetInstance<ShowWeatherViewModel>(); }
    }

    public ApplicationViewModel ApplicationViewModel
    {
        get { return SimpleIoc.Default.GetInstance<ApplicationViewModel>(); }
    }

    public ShowWeatherDetailPage ShowWeatherDetailPage
    {
        get { return SimpleIoc.Default.GetInstance<ShowWeatherDetailPage>(); }
    }

    public ShowWeatherDetailViewModel ShowWeatherDetailViewModel
    {
        get { return SimpleIoc.Default.GetInstance<ShowWeatherDetailViewModel>(); }
    }
}

ApplicationViewModel

public class ApplicationViewModel : ViewModelBaseClass
{
    private Page _currentPage = IocContainer.Ioc.ShowWeatherPage;

    public Page CurrentPage
    {
        get
        {
            return _currentPage;
        }
        set
        {
            if (_currentPage != value)
            {
                _currentPage = value;
            }
        }
    }

    public void Navigate(Type sourcePageType)
    {
        if (sourcePageType.Equals(typeof(ShowWeatherDetailPage)))
        {
            IocContainer.Ioc.ShowWeatherDetailViewModel.Item = 
                                  IocContainer.Ioc.ShowWeatherViewModel.SelectedVillage;
            CurrentPage = IocContainer.Ioc.ShowWeatherDetailPage;
        }

        OnPropertyChanged(nameof(CurrentPage));
    }
}

ShowWeatherViewModel

public class ShowWeatherViewModel: ViewModelBaseClass
{
    public Item SelectedVillage
    {
        get
        {
            return _selectedVillage;
        }
        set
        {
            if (_selectedVillage != value)
            {
                _selectedVillage = value;
                ShowDetailPage();
            }
        }
    }

    private void ShowDetailPage()
    {
        ApplicationViewModel appVm = new ApplicationViewModel();
        appVm.Navigate(typeof(ShowWeatherDetailPage));
    }
}

ShowWeatherDetailViewModel

public class ShowWeatherDetailViewModel: ViewModelBaseClass
{
    private Item _item;

    public Item Item
    {
        get { return _item; }
        set { _item = value; }
    }
}

ViewModelBaseClass

public class ViewModelBaseClass: INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        else
        {
            Debug.WriteLine("PropertyChanged is null");
        }
    }
}

MainPage

<Page
    x:Class="BALaboVoorbeeld.UWP.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:BALaboVoorbeeld.UWP"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    DataContext="{Binding Source={StaticResource ioc}, Path=ApplicationViewModel}"
    mc:Ignorable="d">

    <Grid removed="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Page Content="{Binding CurrentPage, Mode=TwoWay}" />
    </Grid>
</Page>

ShowWeatherPage

<Page
    x:Class="BALaboVoorbeeld.UWP.Pages.ShowWeatherPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:BALaboVoorbeeld.UWP.Pages"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    DataContext="{Binding Source={StaticResource ioc}, Path=ShowWeatherViewModel}"
    mc:Ignorable="d" Width="450">

    <Grid removed="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="100" />
            <ColumnDefinition Width="240" />
            <ColumnDefinition Width="60" />
            <ColumnDefinition Width="1*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="1" />
            <RowDefinition Height="40" />
            <RowDefinition Height="1*" />
            <RowDefinition Height="40" />
        </Grid.RowDefinitions>
        <TextBlock Text="Village:" 
                   HorizontalAlignment="Right" Margin="4" VerticalAlignment="Center"
                   Grid.Row="1" Grid.Column="0" />
        <TextBox HorizontalAlignment="Stretch" Margin="4" VerticalAlignment="Center"
                 Grid.Row="1" Grid.Column="1" Text="{Binding Village, Mode=TwoWay}" />
        <Button  HorizontalAlignment="Stretch" Margin="4" VerticalAlignment="Center"
                 Grid.Row="1" Grid.Column="2" Command="{Binding ShowWeahter}" >
            <SymbolIcon Symbol="Find" />
        </Button>
        <ListBox Grid.Row="2" Grid.Column="0"  Grid.ColumnSpan="3"
                 ItemContainerStyle="{StaticResource lstidflt}" SelectedItem="{Binding SelectedVillage, Mode=TwoWay}"
                 ItemTemplate="{StaticResource weatheritemdt}" ItemsSource="{Binding VillageList}" />
    </Grid>
</Page>