Read-only Run elements in a WPF RichTextBox?

.net-3.5, richtextbox, wpf, xaml

Solution

Alright, I've come up with a solution that works for my case - but may not work for everyone who wants something like this. It's messy, but it does the job.

I'm not going to accept my own answer for a few days, just in case someone else has a better way of accomplishing this.

Here we go, first, the XAML:

<Window x:Class="WpfApplication1.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1"
        Height="500"
        Width="600">
    <DockPanel LastChildFill="True">
        <RichTextBox x:Name="rtb"
                     FontFamily="Courier New"
                     FontSize="14"
                     PreviewKeyDown="rtb_PreviewKeyDown">
            <FlowDocument>
                <Paragraph>
                    <InlineUIContainer Unloaded="InlineUIContainer_Unloaded">
                        <TextBlock FontFamily="Courier New" FontSize="14">This line of text is not editable.</TextBlock>
                    </InlineUIContainer>
                    <Run Foreground="Blue">But this is editable.</Run>
                </Paragraph>
            </FlowDocument>
        </RichTextBox>
    </DockPanel>
</Window>

And the code behind:

using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void InlineUIContainer_Unloaded(object sender, RoutedEventArgs e)
        {
            (sender as InlineUIContainer).Unloaded -= new RoutedEventHandler(InlineUIContainer_Unloaded);

            TextBlock tb = new TextBlock();
            tb.FontFamily = new FontFamily("Courier New");
            tb.FontSize = 14;
            tb.Text = "This line of text is not editable.";

            TextPointer tp = rtb.CaretPosition.GetInsertionPosition(LogicalDirection.Forward);
            InlineUIContainer iuic = new InlineUIContainer(tb, tp);
            iuic.Unloaded += new RoutedEventHandler(InlineUIContainer_Unloaded);
        }

        private void rtb_PreviewKeyDown(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Enter)
            {
                var newPointer = rtb.Selection.Start.InsertLineBreak();
                rtb.Selection.Select(newPointer, newPointer);

                e.Handled = true;
            }
        }
    }
}

My solution relies on the fact that when an `InlineUIContainer` is removed from the UI, it's `Unloaded()` method is called. At that point, I simply reinsert the deleted `InlineUIContainer` at the current caret position.

As with any hack, there are a bunch of disadvantages. The disadvantages I'm finding are the following:

- The text I want to be read-only needs to be wrapped in a `InlineUIContainer`. That is a little limiting for this solution.

- I have to capture the 'Enter' key and insert line breaks manually, otherwise, `InlineUIContainer.Unloaded()` keeps firing everytime the Enter key is pressed. Not fun, but it works for my case.

It's not a great solution, but I think it will work for me. Like I said, I'm not going to mark this as an answer to my own question yet - hopefully someone else will have a better way of doing this.

Problem

Original source