Create Wizard with MVVM Pattern - Databinding and GUI Update not working - mvvm

Question

I am creating a Wizard for automatic Report generating. Therefore the user enters a couple of Issues to the Mainwindow and after he finished, he can create an automatically filled report by clicking a button. Also he need to switch between the entered Issuses (Therefore I put the issues to a list of the Type "Compliant".
The MainWindow contains different controls, in which the user can enter some information.
All controls are binded to the Model like this way (example for a textbox):
Text="{Binding Path=SingleCompliant.Text, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
"SingleCompliant" is an object of the ViewModel of the type "Compliant" (part of the Model), which contains all attributes needed for one Issue.
When I load the Application for the first time, everything works fine.
But when I click on "SaveCompliantAndNext", the binding between "SingleCompliant" Object gets lost and the GUI is not updating. In this Method (raised by a command) I create a new SingleCompliant Object.
What do I need to do for getting a new Object with an empty gui, so the user can continue entereing the next Issue?
This is the ViewModel with implemented "PropertyChanged" Handling:
public class Compliant_ViewModel : ObservableCollection<Compliant> //INotifyPropertyChanged
{
/// <summary>
/// MainWindow Controls are binded to Attributes of this object
/// </summary>
private Compliant _SingleCompliant;
public ObservableCollection<Compliant> CompliantListReport
{
get { return _CompliantListReport; }
private set { _CompliantListReport = value; }
}
/// <summary>
/// Beandstandungs-Objekt
/// </summary>
public Compliant SingleCompliant
{
get { return _SingleCompliant; }
set
{ _SingleCompliant = value;
OnPropertyChanged("SingleCompliant");
}
}
/// <summary>
/// Load next Compliant to the GUI
/// </summary>
public NextCompliant_Command NextCompliant_command { get; private set; }
/// <summary>
/// Load previous Compliant to the GUI
/// </summary>
public PreviousCompliant_Command PreviousCompliant_Command { get; private set; }
/// <summary>
/// Constructor
/// </summary>
public Compliant_ViewModel()
{
SingleCompliant = new Compliant();
CompliantListReport = new ObservableCollection<Compliant>();
NextCompliant_command = new NextCompliant_Command(SaveCompliantAndNext);
PreviousCompliant_Command = new PreviousCompliant_Command(LoadPreviousCompliant);
CreateReport_Command = new CreateReport_Command(CreateReport);
}
public void SaveCompliantAndNext()
{
CompliantListReport.Add(SingleCompliant);
// >>>>> Not working - databinding get lost and gui not updating
SingleCompliant = new Compliant();
}
public void LoadPreviousCompliant()
{
if (this.SingleCompliant.CompliantID > 0)
{ this.SingleCompliant = this.CompliantListReport[this.SingleCompliant.CompliantID - 1]; }
else
{ this.SingleCompliant = this.CompliantListReport[0]; }
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyname)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{ handler(this, new PropertyChangedEventArgs(propertyname)); }
}
}
This is the Model:
public class Compliant : INotifyPropertyChanged
{
public string _Text;
public string Text
{
get { return _Text; }
private set
{
_Text = value;
OnPropertyChanged("Text");
}
}
#region Konstruktoren
public Compliant()
{ }
#region Interface
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyname)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyname));
}
}
#endregion Interface
}
XAML:
Example for one Textbox:
<TextBox Text="{Binding Path=SingleCompliant.Text, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" x:Name="Text" />
XAML Buttons to switch between the Compliants (Issues):
<!--Previous Compliant (Issue)-->
<Button x:Name="BtnBack_Compliant" Content="{DynamicResource Back}" Command="{Binding PreviousCompliant_Command}"/>
<!--Next Compliant (Issue)-->
<Button x:Name="BtnForeward_Compliant" Content="{DynamicResource Foreward}" Command="{Binding NextCompliant_command}" />
What do I make wrong?