WinForms RichTextBox - InvalidOperationException: Cannot load the text - happens only in .Net 6

WPF-Learner 106

I'm using System.Windows.Forms.RichTextBox, and have the following code:

var testRichTextBox = new System.Windows.Forms.RichTextBox();
var testText = @"{\rtf1\ansi\deff0{\fonttbl{\f0 Courier New;}}{\colortbl\red0\green0\blue0;}\fs20{\cf0 \ud{\u160}}\line }";
testRichTextBox.Rtf = testText;

This same code works perfectly in .Net 4.7.2.

When trying to run it in .Net 6, the following exception is produced:

System.InvalidOperationException: Cannot load the text.
   at System.Windows.Forms.RichTextBox.StreamIn(Stream data, SF flags)
   at System.Windows.Forms.RichTextBox.StreamIn(String str, SF flags)
   at System.Windows.Forms.RichTextBox.set_Rtf(String value)

Couldn't find any documentation about it in the WinForms breaking changes in .Net 6 on MSDN, what can be the cause for that?

David Lowndes 4,711 Reputation points

2022-02-01T16:51:29.037+00:00

I can reproduce the same with your RTF string, however, with a different one there's no problem, so is that RTF strictly correct (I don't know)?
Is it perhaps something that you got away with under .NET FW?
WPF-Learner 106 Reputation points

2022-02-01T17:40:44.253+00:00
I think it's related to the \ud{\u160}
I can see the following code when building the RTF text:

if (rtfChar[i] > 127) sb.Append("\\ud{\\u" + (int)rtfChar[i] + "}");

I believe it was added because

Note that while RTF escapes (\'xx) are valid for all characters, the only characters that have to be escaped are these three characters: {, }, and \, plus all the characters over code 127.

https://www.oreilly.com/library/view/rtf-pocket-guide/9781449302047/ch04.html
David Lowndes 4,711 Reputation points

2022-02-01T17:53:51.08+00:00

Yes, I've also found that:
\u160?
works even though \u160 causes the exception.

I'd be inclined to submit a bug report on it on the grounds that it works in .NET FW - if only to see what MS's official response is.
If you do submit a bug report on it, please post a link to your report here and I'll confirm it.

Accepted answer

Viorel 112.9K Reputation points

2022-02-01T17:55:58.213+00:00

To use this form of \ud, try adding \uc0 (after \ansi, for example).
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David Lowndes 4,711 Reputation points

2022-02-01T17:57:37.03+00:00

Yes, that works for me too.

WPF-Learner 106 Reputation points

2022-02-01T18:21:16.053+00:00

@Viorel Thank you, this now works on .Net 6:

var testRichTextBox = new System.Windows.Forms.RichTextBox(); var testText = @"{\rtf1\ansi\uc0\deff0{\fonttbl{\f0 Courier New;}}{\colortbl\red0\green0\blue0;}\fs20{\cf0 \ud{\u160}}\line }"; testRichTextBox.Rtf = testText;

Could you please explain a bit why the \uc0 is required? I really appreciate your help, thank you!

Viorel 112.9K Reputation points

2022-02-01T18:33:07.423+00:00

If your characters will not be always representable and you want to replace ‘\u160’ with some other text, ‘XY’ for example, then you can specify ‘\uc2’ and write ‘\u160XY’. But if you do not need such replacements, then use ‘\uc0’ and ‘\u160’. It seems that it is ‘\uc1’ by default, therefore ‘}’ from ‘{\u160}’ is interpreted as replacement, which results in unbalanced ‘{ }’.

WPF-Learner 106 Reputation points

2022-02-01T21:17:15.47+00:00

@Viorel I'm also wondering why wasn't it required in the .Net framework, but only now, in .Net6 (I mean, wasn't this situation with unbalanced ‘{ }’ caused also in .Net framework?).

Thank you!

Viorel 112.9K Reputation points

2022-02-01T22:31:59.963+00:00

Probably the previous Rich Edit control was tolerant to some kinds of RTF inconsistencies. For example, the old LoadFile function seems to accept files that do not contain the final ‘}’.
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WinForms RichTextBox - InvalidOperationException: Cannot load the text - happens only in .Net 6

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