[chenjt2001]

What does the pull request do?

Fixes incorrect caret positioning in TextBox when TextAlignment is set to Center and the final arranged width differs from the width used during measure.

Adds a regression test covering the case where the TextLayout is recreated during arrange.

What is the current behavior?

<Window xmlns="https://github.com/avaloniaui"
        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"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="TextBoxCaretRepro.MainWindow"
        Title="TextBoxCaretRepro">
    <StackPanel Margin="40" Spacing="20">

        <TextBlock Text="Type into the centered TextBox:" FontSize="18" />

        <TextBox Width="400"
                 FontSize="32"
                 TextAlignment="Center"
                 HorizontalAlignment="Center" />

    </StackPanel>
</Window>

TextBoxCaretRepro.2026-09-29.11-00-59.mp4

What is the updated/expected behavior with this PR?

The caret position is recalculated against the same TextLayout that is used to render the text.

As a result, the caret remains correctly positioned when the text is centered, including after the layout is recreated with a different arranged width.

How was the solution implemented (if it's not obvious)?

TextPresenter already marks the caret bounds as dirty whenever a new TextLayout is created.

Previously, when ArrangeOverride invalidated and recreated the layout due to a changed final width, the dirty caret bounds were not recalculated before the caret was rendered.

The fix ensures that the caret bounds are recalculated against the newly created layout after the arranged width changes.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

None.

Obsoletions / Deprecations

None.

Fixed issues

Regression introduced by PR #22176.

[Gillibald]

LGTM with some small nit mentioned in the comments

[github-actions]

NuGet packages

The packages for this pull request have been published (workflow run):

• Version: 12.2.999-cibuild0100255-alpha
• Feed URL: https://nuget-feed-all.avaloniaui.net/v3/index.json

[fholmquist]

Thanks for this. The same regression from AvaloniaUI/Avalonia#22176 shows up with left-aligned, wrapped text too (TextWrapping="Wrap"), not only centered text. When a line's last word fits in Math.Ceiling(finalWidth) but not in the measure width, the drawn layout and the caret's layout wrap differently. Every caret on the following lines is then drawn a word to the right, and Up/Down move from the wrong spot. Seen on 12.1.3 on Windows, with a TextBox inside a LayoutTransformControl at 0.85 scale and 225% DPI: a caret at the start of line 2 was drawn after the first word. Re-placing the caret on the drawn layout after layout (what this PR does in ArrangeOverride) fixes it in our app. We'd welcome the 12.1.x backport.

[cla-avalonia]

• All contributors have signed the CLA.

[chenjt2001]

@cla-avalonia agree