MVVM/WPF: DataTemplate is not changed in Wizard

Question

Hello,

I wonder why my contentcontrol(headeredcontentcontrol) does not change the datatemplates when I press the previous/next button. While debugging everything seems ok means I jump forth and back the collection of wizardpages but always the first page is shown and its header text not the usercontrol is visible.

What do I have forgotten?

I do not have code-behind code.

namespace TBM.ViewModel { public class WizardMainViewModel {
WizardPageViewModelBase _currentPage; ReadOnlyCollection _pages;

    RelayCommand _moveNextCommand;
    RelayCommand _movePreviousCommand;     

    public WizardMainViewModel()
    {            
        this.CurrentPage = this.Pages[0];           
    }        

    public RelayCommand MoveNextCommand      { get { return _moveNextCommand ?? (_moveNextCommand = new RelayCommand(() => this.MoveToNextPage(), () => this.CanMoveToNextPage)); } }  
    public RelayCommand MovePreviousCommand  { get { return _movePreviousCommand ?? (_movePreviousCommand = new RelayCommand( () => this.MoveToPreviousPage(), () => this.CanMoveToPreviousPage)); } }        

    bool CanMoveToPreviousPage
    {
        get { return 0 < this.CurrentPageIndex; }
    }      

    bool CanMoveToNextPage
    {
        get { return this.CurrentPage != null && this.CurrentPage.IsValid(); }
    }

    void MoveToPreviousPage()
    {           
        this.CurrentPage = this.Pages[this.CurrentPageIndex - 1];
    }

    void MoveToNextPage()
    {
        if (this.CurrentPageIndex < this.Pages.Count - 1)
            this.CurrentPage = this.Pages[this.CurrentPageIndex + 1];                      
    }             

    /// <summary>
    /// Returns the page ViewModel that the user is currently viewing.
    /// </summary>
    public WizardPageViewModelBase CurrentPage
    {
        get { return _currentPage; }
        private set
        {
            if (value == _currentPage)
                return;

            if (_currentPage != null)
                _currentPage.IsCurrentPage = false;

            _currentPage = value;

            if (_currentPage != null)
                _currentPage.IsCurrentPage = true;

            this.OnPropertyChanged("CurrentPage");
            this.OnPropertyChanged("IsOnLastPage");
        }
    }


    public bool IsOnLastPage
    {
        get { return this.CurrentPageIndex == this.Pages.Count - 1; }
    }

    /// <summary>
    /// Returns a read-only collection of all page ViewModels.
    /// </summary>
    public ReadOnlyCollection<WizardPageViewModelBase> Pages
    {
        get { return _pages ?? CreatePages(); }            
    } 

    ReadOnlyCollection<WizardPageViewModelBase> CreatePages()
    {
        WizardPageViewModelBase welcomePage = new WizardWelcomePageViewModel();
        WizardPageViewModelBase schoolclassPage = new WizardSchoolclassSubjectPageViewModel();
        WizardPageViewModelBase lessonPage = new WizardLessonTimesPageViewModel();
        WizardPageViewModelBase timetablePage = new WizardTimeTablePageViewModel();
        WizardPageViewModelBase finishPage = new WizardFinishPageViewModel();

        var pages = new List<WizardPageViewModelBase>();
        pages.Add(welcomePage);
        pages.Add(schoolclassPage);
        pages.Add(lessonPage);
        pages.Add(timetablePage);
        pages.Add(finishPage);

        return _pages = new ReadOnlyCollection<WizardPageViewModelBase>(pages);
    }

    int CurrentPageIndex
    {
        get
        {
            if (this.CurrentPage == null)
            {
                Debug.Fail("Why is the current page null?");
                return -1;
            }
            return this.Pages.IndexOf(this.CurrentPage);
        }
    } 

    public event PropertyChangedEventHandler PropertyChanged;
    void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }      
}

}

<UserControl x:Class="TBM.View.WizardMainView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:ViewModel="clr-namespace:TBM.ViewModel"
         xmlns:View="clr-namespace:TBM.View"
         mc:Ignorable="d" 
         >

<UserControl.Resources>

    <DataTemplate DataType="{x:Type ViewModel:WizardWelcomePageViewModel}">
        <View:WizardWelcomePageView />
    </DataTemplate>

    <DataTemplate DataType="{x:Type ViewModel:WizardSchoolclassSubjectPageViewModel}">
        <View:WizardSchoolclassSubjectPageView />
    </DataTemplate>

    <DataTemplate DataType="{x:Type ViewModel:WizardLessonTimesPageViewModel}">
        <View:WizardLessonTimesPageView />
    </DataTemplate>

    <DataTemplate DataType="{x:Type ViewModel:WizardTimeTablePageViewModel}">
        <View:WizardTimeTablePageView />
    </DataTemplate>

    <DataTemplate DataType="{x:Type ViewModel:WizardFinishPageViewModel}">
        <View:WizardFinishPageView />
    </DataTemplate>

    <!-- This Style inherits from the Button style seen above. -->
    <Style BasedOn="{StaticResource {x:Type Button}}" TargetType="{x:Type Button}" x:Key="moveNextButtonStyle">
        <Setter Property="Content" Value="Next" />
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=IsOnLastPage}" Value="True">
                <Setter Property="Content" Value="Finish}" />
            </DataTrigger>
        </Style.Triggers>
    </Style>

    <ViewModel:WizardMainViewModel x:Key="WizardMainViewModelID" />      

</UserControl.Resources>

<Grid DataContext="{Binding ., Source={StaticResource WizardMainViewModelID}}" >
    <Grid.RowDefinitions>
        <RowDefinition Height="310*" />
        <RowDefinition Height="51*" />
    </Grid.RowDefinitions>

    <!-- CONTENT -->
    <Grid  Grid.Row="0" Background="LightGoldenrodYellow">
        <HeaderedContentControl Content="{Binding CurrentPage}" Header="{Binding Path=CurrentPage.DisplayName}"  />
    </Grid>

    <!-- NAVIGATION BUTTONS -->
    <Grid Grid.Row="1" Background="Aquamarine">
        <StackPanel HorizontalAlignment="Center" Orientation="Horizontal">
            <Button Command="{Binding MovePreviousCommand}" Content="Previous" />
            <Button Command="{Binding MoveNextCommand}" Style="{StaticResource moveNextButtonStyle}" Content="Next" />
            <Button Command="{Binding CancelCommand}" Content="Cancel" />
        </StackPanel>
    </Grid>
</Grid>