public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class MainViewModel : ViewModelBase
{
    private CurrentTimeViewModel _currentTime;

    public CurrentTimeViewModel CurrentTime
    {
        get { return _currentTime; }
        set
        {
            _currentTime = value;
            OnPropertyChanged();
        }
    }
}

public class CurrentTimeViewModel : ViewModelBase
{
    private string _currentTimeTicks;

    public string CurrentTimeTicks
    {
        get { return _currentTimeTicks; }
        set
        {
            _currentTimeTicks = value;
            OnPropertyChanged();
        }
    }

    public CurrentTimeViewModel()
    {
        Update();
    }

    public void Update()
    {
        CurrentTimeTicks = DateTime.Now.Ticks.ToString();
    }
}

<Page x:Class="CompiledBindings2.MainPage"
      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:local="using:CompiledBindings2"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>

        <StackPanel Margin="12">
            <TextBlock Style="{StaticResource CaptionTextBlockStyle}" Text="Current Time Ticks (Binding)" />
            <TextBlock Style="{StaticResource BodyTextBlockStyle}" Text="{Binding CurrentTime.CurrentTimeTicks}" />

            <TextBlock Style="{StaticResource CaptionTextBlockStyle}" Text="Current Time Ticks (x:Bind)" />
            <TextBlock Style="{StaticResource BodyTextBlockStyle}" Text="{x:Bind ViewModel.CurrentTime.CurrentTimeTicks, Mode=OneWay}" />
        </StackPanel>

        <StackPanel Grid.Row="1">
            <Button HorizontalAlignment="Stretch"
                    Click="CreateChildViewModelButton_OnClick"
                    Content="Create CurrentTimeViewModel" />
            <Button HorizontalAlignment="Stretch"
                    Click="UpdateCurrentTimeViewModelButton_OnClick"
                    Content="Update CurrentTimeViewModel" />
            <Button HorizontalAlignment="Stretch"
                    Click="DestroyCurrentTimeViewModelButton_OnClick"
                    Content="Destroy CurrentTimeViewModel" />
        </StackPanel>
    </Grid>
</Page>

public sealed partial class MainPage : Page
{
    private readonly MainViewModel _viewModel;

    public MainPage()
    {
        this.InitializeComponent();

        _viewModel = new MainViewModel();

        this.DataContext = _viewModel;
    }

    public MainViewModel ViewModel
    {
        get { return _viewModel; }
    }

    private void CreateChildViewModelButton_OnClick(object sender, RoutedEventArgs e)
    {
        _viewModel.CurrentTime = new CurrentTimeViewModel();
    }

    private void UpdateCurrentTimeViewModelButton_OnClick(object sender, RoutedEventArgs e)
    {
        if (_viewModel.CurrentTime != null)
        {
            _viewModel.CurrentTime.Update();
        }
    }

    private void DestroyCurrentTimeViewModelButton_OnClick(object sender, RoutedEventArgs e)
    {
        _viewModel.CurrentTime = null;
    }
}