RichTextBox will not redraw the last pixel column on resize about winforms HOT 11 CLOSED

Is it something that can be tested with MFC? That would isolate it, wouldn't it?

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@Nora-Zhou01 Interesting! I was not able to reproduce it with .NET Framework 4.5.2 (our current target framework version), but did not try it with .NET Framework 4.8 tho.

It looks like the bug was introduced between .NET Framework 4.5.2 and 4.8.

Also I was able to reproduce the bug with an last letter of "a" and a initial width of 292.

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@merriemcgaw @elachlan @SteffenSchwaiger we can add below quirk in App.config file to disable richedit30.dll for RichTextBox control when project target to .NET Framework 4.8 or 4.8.1.

	<runtime>
		<AppContextSwitchOverrides value="Switch.System.Windows.Forms.DoNotLoadLatestRichEditControl=true"/>
	</runtime>

In .NET Project, we can create a new RichTextBox2 class to use the richedit20.dll version. Like below code snippet:

    public class RichTextBox2 : RichTextBox
    {
        protected override CreateParams CreateParams
        {
            get
            {
                if (moduleHandle == IntPtr.Zero)
                {
                    moduleHandle = LoadLibrary("Riched20.dll");
                    if ((long)moduleHandle < 0x20) throw new Win32Exception(Marshal.GetLastWin32Error(), "Could not load Riched20.dll");
                }
                var cp = base.CreateParams;
                cp.ClassName = "RichEdit20W";
                return cp;
            }
        }
        private static IntPtr moduleHandle;

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        static extern IntPtr LoadLibrary(string lpFileName);
    }

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Excellent bug report! Thank your for the image diff.

@Olina-Zhang can your team please test this?

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This issue is reproduced in both .NET framework4.8.1 projects and .NET Core projects, if there is a rendering, it will disappear after adjusting the size of the form.the results are as follows:

Trying to change the last character "r" to other characters does not reproduce this issue.
The issue is not reproduced in the TextBox control. After clicking the resize button, the character line does not change and no rendering occurs,the results are as follows:

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We updated the version of riched20.dll that we wrapped sometime around 4.6 if memory serves. @Tanya-Solyanik do you recall? I wouldn't be surprised if this is more of a Windows/Richedit issue than something WinForms is able to control directly.

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@Olina-Zhang can your team go ahead and test this in MFC?
@KlausLoeffelmann - you said you were touching the RichTextBox potentially so keep this in mind when you do.

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@John-Qiao can you please test MFC to verify it is indeed a newer richedit version issue?

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@elachlan I'm not familiar with MFC project, I will try to create a MFC project and test it, but I'm not sure if it will work.

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Maybe @Olina-Zhang can help?

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@SteffenSchwaiger this bug is about which version of the Rich Text Box control is loaded at runtime by WinForms. @John-Qiao has provided instructions above to reference the earlier versions, which may not produce this issue. This is something that would need a fix from the Office team and Windows to take the fix. I would recommend following @John-Qiao's approach instead.

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