Why doesn't my RichTextBox change the text when I type it?

Question

I have a RichTextbox and now I am typing some text. The text is also changed in the view, but if I now want to get to the text in the code behind, it always gives me the placeholder text and not the one I entered.

Which means that first look(PlaceHolder):

Placeholder

Code from The RichTextBox:

<Grid Grid.Row="2">
    <RichTextBox x:Name="rtb1" IsHitTestVisible="True" HorizontalAlignment="Right" 
            TextChanged="OnDocumentChanged" BorderThickness="0" FontSize="40"
            Background="Transparent" Panel.ZIndex="2">                  
        <FlowDocument TextAlignment="Center" >
            <Paragraph >
                <Run Text="Hallo" />
            </Paragraph>
        </FlowDocument>
    </RichTextBox>
    <TextBox x:Name="tb1" Style="{StaticResource tb1}" Text="Eingabe"
        FontSize="40" TextWrapping="Wrap" Panel.ZIndex="1"
        TextAlignment="Center" Foreground="DarkGray">
    </TextBox>
</Grid>

Then my change in the View:

ViewChange

And then I try to get the Text From Code behind:

string richText = new TextRange(rtb1.Document.ContentStart, rtb1.Document.ContentEnd).Text;
MessageBox.Show(richText);

But the Output is this:

Output

How Can I get that what I have written in Code Behind?

Answer 1

I adjusted your script a bit by removing the <FlowDocument/> and replacing it with manual Width and Height.

Try this:

<Grid Grid.Row="2">
    <RichTextBox x:Name="rtb1" IsHitTestVisible="True" HorizontalAlignment="Center" 
        TextChanged="rtb1_TextChanged" BorderThickness="0" FontSize="40"
        Background="Transparent" Panel.ZIndex="2" Width="400" Height="100" 
        VerticalAlignment="Top" Cursor="Arrow"/>
    <TextBox x:Name="tb1" Text="Eingabe" FontSize="40" TextWrapping="Wrap" 
    Panel.ZIndex="1" TextAlignment="Center" Foreground="DarkGray"/>
</Grid>

And I added a try-catch to the script so you can debug easier:

try
{
    string richText = new TextRange(rtb1.Document.ContentStart, rtb1.Document.ContentEnd).Text;
    Console.WriteLine(richText);
    MessageBox.Show(richText);
} 
catch (System.Windows.Markup.XamlParseException ex)
{
    Console.WriteLine(ex.StackTrace);
}

It works for me