How to check if I delete (Backspace, Delete or "Cut") UIElement in RichTextBox?

Question

I have RichTextBoxone that should contain some buttons that should be removed properly (processed) when the user edits the content in it. I can check if I am deleting (Backspace, Delete or Cut) text (characters) but not the control <Button>.

The attached code that I used:

XAML:

<RichTextBox x:Name="tRTB"
             HorizontalAlignment="Left"
             Keyboard.PreviewKeyDown="tRTB_PreviewKeyDown"
             PreviewTextInput="tRTB_PreviewTextInput">
   <local:EnabledFlowDocument x:Name="tFD">
      <Paragraph x:Name="tP"/>                 
   </local:EnabledFlowDocument>
</RichTextBox>

WITH#:

public void AppendNewButton(int i)
{
    Button addB = new Button();
    addB.Content = i;
    addB.HorizontalAlignment = HorizontalAlignment.Left;

    tP.Inlines.Add(addB);
    tP.Inlines.Add("Bk" + i.ToString()); //appends a button and text in RTB
}

and event:

private void tRTB_PreviewKeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Back)
    {
        var start = tRTB.CaretPosition;
        var t = start.GetTextInRun(LogicalDirection.Backward);
        var end = start.GetNextContextPosition(LogicalDirection.Backward);
        var t1 = end.GetTextInRun(LogicalDirection.Backward);

        tRTB.Selection.Select(start, end);
        tRTB.Selection.ApplyPropertyValue(TextElement.ForegroundProperty, Brushes.Black);
        tRTB.Selection.Select(start, start);

        //should handle deletion of button here
        /* if (button is before cursor) */
        /* e.Handled=true; */
    }
}

I understand that it only start.GetTextInRungets the text, and I get the value "" ( null) when the button is clicked back. But I also tried start.GetAdjacentElement, but I was not able to get <Button>in the same condition.

Answer 1

(), Backspace, RichTextBox PreviewKeyDown. , , , . :

<Window x:Class="WpfApplication4.MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="MainWindow" Height="350" Width="525">
  <Grid>
    <RichTextBox 
      x:Name="tRTB"
      HorizontalAlignment="Left"
      Keyboard.PreviewKeyDown="tRTB_PreviewKeyDown">
    </RichTextBox>
  </Grid>
</Window>

...

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    public void AppendNewButton(int i)
    {
        Button addB = new Button();
        addB.Content = i;
        addB.HorizontalAlignment = HorizontalAlignment.Left;

        var insertionPosition = tRTB.CaretPosition.GetInsertionPosition(LogicalDirection.Forward);

        var inline = new InlineUIContainer(addB);
        insertionPosition.Paragraph.Inlines.InsertAfter(
            (Inline)insertionPosition.Parent,
            inline);

        tRTB.CaretPosition = tRTB.CaretPosition.GetNextInsertionPosition(LogicalDirection.Forward);
    }

    public void tRTB_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.B)
        {
            AppendNewButton(7);
            e.Handled = true;
        }
    }
}