Enabling SpellChecker in RichTextEditor causes text to become invisible [WPF]

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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I found an interesting problem for which I'm unable to find a fix for. Enabling the spellchecker in the RichTextBox component causes text to disappear randomly, sometimes whilst scrolling, sometimes whilst writing. The text is still there, it's just invisible. The invisible text can be selected, the caret can be placed in it, and writing causes it to become visible and sometimes the next line then becomes invisible. The code to reproduce is quite simple, all that is required is the RTB component with the spellchecker enabled. I was unable to find anything similar to this problem, is this a known issue? Is there a workaround?

 Code to reproduce (xaml): 

<Window x:Class="WpfTestRtb.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfTestRtb"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
        <Grid>
          <Grid.ColumnDefinitions>
              <ColumnDefinition Width="*"/>
          </Grid.ColumnDefinitions>
          <Grid.RowDefinitions>
              <RowDefinition Height="*"/>
          </Grid.RowDefinitions>
          <RichTextBox Grid.Column="0" Grid.Row="0" SpellCheck.IsEnabled="True" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" VerticalScrollBarVisibility="Auto" />
      </Grid>
</Window>

Code to reproduce (cs):

usingSystem;
usingSystem.Collections.Generic;
usingSystem.Linq;usingSystem.Text;
usingSystem.Threading.Tasks;
usingSystem.Windows;
usingSystem.Windows.Controls;
usingSystem.Windows.Data;
usingSystem.Windows.Documents;
usingSystem.Windows.Input;
usingSystem.Windows.Media;
usingSystem.Windows.Media.Imaging;
usingSystem.Windows.Navigation;
usingSystem.Windows.Shapes;
namespace WpfTestRtb
{     
       /// <summary>     
       /// Interaction logic for MainWindow.xaml     
       /// </summary>     
       publicpartialclassMainWindow:Window     
      {         
              publicMainWindow()         
              {             
                   InitializeComponent();        
              }     
      }
}

It's important to note that this error doesn't occur immediately, sometimes you have to write for a while for it to show up, but it does show up. One solution that I have found is that putting the RTB in a ScrollViewer causes the problem to go away. This is not something I can do, however, as from my understanding the scrollviewer breaks virtualization in the editor which slows the RTB down when there's a lot of text. I need the editor to retain its speed whilst showing spelling errors. A closing note, this happens in .NET version >= 4.0, I tested on 3.x and the error did not occur.

Example image #1, invisible text:

Image:92997-example-01.png

Example #2, the invisible text is selected:

Image:92998-example-02.png

Example #3, writing in the selection causes some of the lines to become visible:

Image:92999-example-03.png

I will also include sample RTF that causes this error:

rtf.zip

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Original Comments

Nathan Kawalec on 9/13/2019, 03:00 PM:

I found another question with the same problem, the question is old and I don't think any workarounds were found (apart from not using the RTB).

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Original Solutions

(no solutions)

[nathankawalec]

I'm available for brainstorming if anyone has any ideas :)
I've spent many hours on this specific error, I would love to see it die.

[weltkante]

It should be possible to debug this once the render engine becomes available.

[nathankawalec]

Ok, is there an expected timeline for that?

[weltkante]

I think someone mentioned the current plans somewhere in the preview update posts, but the roadmap document doesn't commit to any timeline. Note that I'm just commenting and not involved with Microsoft or the repository. Right now their priorities are with the upcoming 3.0 release next week, so I just wanted to drop a note that regardless of whether someone from Microsoft takes a look, once the render engine is committed to the repo anyone can debug and fix this (at least for the .NET Core build of WPF)

[nathankawalec]

I understand, thanks for the info :)
I'll be monitoring the repo -- once the render engine gets committed I'll be more than happy to debug this.

[Krudonix]

Hi,

Is there any update or work around on this ? We are getting hit pretty hard.

I tried the above on net8 will same issue.

Regards,

[Kuldeep-MS]

Hi @Krudonix,

We weren't able to look at the issue yet. But will take a look at it soon.

Meanwhile if you can share any details, which is not already shared on the thread, that will be helpful for us to kick start our investigation.

[ashish-chawda]

Hi,

Is there any update or work around on this ? We are getting hit pretty hard.

I tried the above on net8 will same issue.

Regards,

HI All, I am attaching a sample app where the issue is easily replicated, please use attached text file for the paste contents.
TextForPasting.txt
RTESpellCheckIssue.zip

Its uploaded here as well - https://github.com/ashish-chawda/RTERenderingIssue/tree/main/RTESpellCheckIssue

After pasting the text, you can see some lines are invisible or distorted.

[miloush]

Doesn't look like I can reproduce the issue on .NET 8, 125% DPI:

Can you share a screenshot?

[ashish-chawda]

Doesn't look like I can reproduce the issue on .NET 8, 125% DPI:

Can you share a screenshot?

[ashish-chawda]

Any update on above please