在ViewModel构造函数外部更改时，ContentControl视图不更新

Question

当我在构造函数中进行设置时，MainMenuView中的ContentControl将更新，但此后不会更新。我试图让它更改按钮单击。该命令似乎正在运行，并更改了CurrentPageViewModel的值。我正在遵循此代码示例来更改视图https://rachel53461.wordpress.com/2011/12/18/navigation-with-mvvm-2/。

MainMenuViewModel：

public MainMenuViewModel()
    {
        SelectViewCommand = new RelayCommand<IPageViewModel>(s => ChangeViewModel(s));
        PageViewModels.Add(new ClockViewModel());

        CurrentPageViewModel = PageViewModels[1];
    }
    private List<IPageViewModel> pageViewModels;
    public List<IPageViewModel> PageViewModels
    {
        get
        {
            if (pageViewModels == null)
                pageViewModels = new List<IPageViewModel>();

            return pageViewModels;
        }
    }

    private IPageViewModel currentPageViewModel;
    public IPageViewModel CurrentPageViewModel
    {
        get { return currentPageViewModel; }
        set { currentPageViewModel = value; OnPropertyChanged("currentPageViewModel"); }
    }

    public RelayCommand<IPageViewModel> SelectViewCommand { get; private set; }

    private void ChangeViewModel(IPageViewModel viewModel)
    {
        if (!PageViewModels.Contains(viewModel))
            PageViewModels.Add(viewModel);

        CurrentPageViewModel = PageViewModels
            .FirstOrDefault(vm => vm == viewModel);
    }

    private void OnPropertyChanged(string propertyName)
    {
        if (string.IsNullOrEmpty(propertyName))
            throw new ArgumentNullException("propertyName");

        var changed = PropertyChanged;
        if (changed != null)
        {
            changed(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;

MainMenuView：

<Window x:Class="TextApp.View.MainMenuView"
    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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:TextApp.View"
    xmlns:local1="clr-namespace:TextApp.ViewModel"
    mc:Ignorable="d"
    Title="MainMenuView" Height="450" Width="800">
<Window.Resources>
    <DataTemplate DataType="{x:Type local1:ClockViewModel}">
        <local:ClockView/>
    </DataTemplate>
    <DataTemplate DataType="{x:Type local1:IPageViewModel}">
        <local:IPageView/>
    </DataTemplate>
</Window.Resources>
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="0.3*"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <StackPanel Grid.Column="0">
        <ItemsControl ItemsSource="{Binding PageViewModels}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Button Content="{Binding Name}"
                            Command="{Binding DataContext.SelectViewCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
                            CommandParameter="{Binding}"
                            Margin="2,5"/>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </StackPanel>
    <ContentControl Grid.Column="1" Content="{Binding CurrentPageViewModel}"/> 
</Grid>