How to print a "page" from the mainwindow?

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C#

XAML

WPF

In my Program Ive got and Side Panel which is always display and on the left beside the Panel is space for the Pages which I display when I press the the button on the Side Panel of the Page I want to see.

But now Ive got a button which should Print the Page which is selected.

But for some reason the program didnt print what I have written in the RichTextBox, to understand I have an Richtextbox placeholder which looks like that:

<Grid Grid.Row="1" >
    <RichTextBox x:Name="rtb0" IsHitTestVisible="True"
             TextChanged="OnDocumentChanged" BorderThickness="0"
             Background="Transparent" Panel.ZIndex="2">
        <FlowDocument x:Name="fdoc" TextAlignment="Center"/>

        <RichTextBox.Style>
            <Style TargetType="RichTextBox">
                <Setter Property="FontSize" Value="60"/>
            </Style>
        </RichTextBox.Style>
    </RichTextBox>
    <TextBox x:Name="tb0" Style="{StaticResource tb0}" Text="{Binding TextBox1, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
                      TextWrapping="Wrap" Panel.ZIndex="1" TextAlignment="Center"
                     Foreground="DarkGray">

    </TextBox>
    <!--<Grid.Style>
        <Style TargetType="Grid">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition Binding="{Binding TextBox1}" Value=""/>
                        <Condition Binding="{Binding printcontrol}" Value="True"/>
                    </MultiDataTrigger.Conditions>
                    <Setter Property="Visibility" Value="Hidden"/>
                </MultiDataTrigger>
            </Style.Triggers>
        </Style>
    </Grid.Style>-->
</Grid>

and my Style for that:

<Style TargetType="{x:Type TextBox}" x:Key="tb0">
          <Setter Property="BorderThickness" Value="0"/>
          <Setter Property="FontSize" Value="40"/>
          <Style.Triggers>
              <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Page}}, Path=IsDocumentEmpty0}"
                               Value="False">
                  <Setter Property="Visibility" Value="Hidden"/>

              </DataTrigger>

          </Style.Triggers>
      </Style>

and my OnDocumentChange:

  public bool IsDocumentEmpty0
        {
            get { return (bool)GetValue(IsDocumentEmptyProperty0); }
            set { SetValue(IsDocumentEmptyProperty0, value); }
        }
public static readonly DependencyProperty IsDocumentEmptyProperty0 =
          DependencyProperty.Register("IsDocumentEmpty0", typeof(bool), typeof(A4Page), new PropertyMetadata(false));

 private void OnDocumentChanged(object sender, TextChangedEventArgs e)
        {
            if (sender is RichTextBox richText)
            {
                if (richText.Name == "rtb0")
                {
                    int size = rtb0.Document.ContentStart.GetOffsetToPosition(rtb0.Document.ContentEnd);
                    IsDocumentEmpty0 = (size == 0 // The document has not blocks. Example, after Ctrl+A & Delete. 
                            || size == 2 // The document has 1 block without inlines. For example, 1 paragraph without inline(s).  
                            || size == 4); // The document has 1 block and 1 paragraph with empty inline. 
                }
               
            }
        }

Thats all for that I have an Placholder for an RichTextBox. Now when I print I want to hide all Placeholder that not be used. And thats working ( for that I have the printcontrol Property) but now when I want to print I always get the Page with the placeholder text and not with the text I wrote.

What I have tried:

For that I tried this on my MainWindow:

var vm = (ViewModel)this.DataContext;
           A4Page page = new A4Page();
           page.print();

And that On my Page the Print Method:

var vm = (ViewModel)this.DataContext;
            vm.printcontrol = true;
            PrintDialog printDlg = new PrintDialog();
            int i = 0;
            LocalPrintServer printServer = new LocalPrintServer();

            PrintQueueCollection printQueuesOnLocalServer = printServer.GetPrintQueues(new[] { EnumeratedPrintQueueTypes.Local, EnumeratedPrintQueueTypes.Connections });


            foreach (PrintQueue printer in printQueuesOnLocalServer)

            {
                printDlg.PrintQueue = new PrintQueue(new PrintServer(), printer.Name);
                //break;
                //if (printer.Name == "Kyocera ECOSYS P3045dn (2)")
                i++;
                if(i == 3)
                    break;
            }
            // printDlg.PrintQueue = new PrintQueue(new PrintServer(),vm.selected_printer);
            printDlg.PrintTicket.CopyCount = vm.PrintCount;

          

            printDlg.PrintTicket.PageMediaSize = new PageMediaSize(PageMediaSizeName.ISOA4); ///Setzt die Richtige Größe
            printDlg.PrintTicket.PageOrientation = PageOrientation.Portrait;///Setzt das Document auf Vertical Drucken

            printDlg.PrintVisual(PageA4, "Page Printing.");
            vm.printcontrol = false;

But For Some reason its always empty the Richtextbox when I press the print button on my Sidepanel.

I tried to get the text manuel from my RichTextBox with that:

string richText = new TextRange(rtb0.Document.ContentStart, rtb0.Document.ContentEnd).Text;

but for some reason Its always empty