Fix RichTextBox flooding AT channel with entire document on focus#14675
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trypsynth wants to merge 1 commit into
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Fix RichTextBox flooding AT channel with entire document on focus#14675trypsynth wants to merge 1 commit into
trypsynth wants to merge 1 commit into
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Removes the explicit UIA automation notification from OnGotFocus that was sending the full Text of the control to assistive technology on every focus event. For large documents this caused NVDA and JAWS to freeze, and produced a double-announcement (the native MSAA focus event already reads the current line correctly). The pass-through override is kept to satisfy the shipped public API surface. Closes dotnet#14671
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Pull request overview
This PR addresses an accessibility/performance issue in RichTextBox where focusing the control could flood assistive technology with the entire document text via a UIA automation notification, leading to freezes (notably NVDA/JAWS) and duplicate announcements.
Changes:
- Removes the UIA automation notification emission from
RichTextBox.OnGotFocus, leaving a pass-through override to preserve the existing API surface. - Updates the unit test to assert that focusing no longer triggers
InternalRaiseAutomationNotification.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/System.Windows.Forms/System/Windows/Forms/Controls/RichTextBox/RichTextBox.cs | Removes focus-time UIA notification behavior while keeping an override that delegates to base. |
| src/test/unit/System.Windows.Forms/System/Windows/Forms/RichTextBoxTests.cs | Updates/renames the focus test to verify no automation notification is raised on focus. |
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| public void RichTextBox_OnGotFocus_DoesNotRaiseAutomationNotification(EventArgs eventArgs) | ||
| { | ||
| // NVDA and JAWS already announce the focused line via native MSAA on focus; an additional | ||
| // UIA automation notification caused the line to be read twice. The correct behaviour is |
| [WinFormsTheory] | ||
| [NewAndDefaultData<EventArgs>] | ||
| public void RichTextBox_OnGotFocus_RaisesAutomationNotification_WithText(EventArgs eventArgs) | ||
| public void RichTextBox_OnGotFocus_DoesNotRaiseAutomationNotification(EventArgs eventArgs) |
| Text); | ||
| } | ||
| } | ||
| protected override void OnGotFocus(EventArgs e) => base.OnGotFocus(e); |
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Fixes #14671
Proposed changes
Removes the explicit UIA automation notification from OnGotFocus that was sending the full Text of the control to assistive technology on every focus event. For large documents this caused NVDA and JAWS to freeze, and produced a double-announcement (the native MSAA focus event already reads the current line correctly). The pass-through override is kept to satisfy the shipped public API surface.
Customer Impact
Any rich text box with a lot of content in it risks freezing user's assistive technologies.
Regression?
Risk
Test methodology
Created a basic winforms app, created a RichTextBox inside it, gave it 6 lines, tested without my custom assembly and with, my custom version fixes the bug.
Accessibility testing
Tested with NVDA on Windows 11 24H2.
Test environment(s)
.NET SDK:
Version: 10.0.202
Commit: 1e7d5a8ae3
Workload version: 10.0.200-manifests.f96d7f23
MSBuild version: 18.3.3+1e7d5a8ae
Runtime Environment:
OS Name: Windows
OS Version: 10.0.26100
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\10.0.202\
.NET workloads installed:
There are no installed workloads to display.
Configured to use workload sets when installing new manifests.
No workload sets are installed. Run "dotnet workload restore" to install a workload set.
Host:
Version: 10.0.6
Architecture: x64
Commit: 47fb725acf
.NET SDKs installed:
10.0.202 [C:\Program Files\dotnet\sdk]
.NET runtimes installed:
Microsoft.AspNetCore.App 10.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 10.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 10.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Other architectures found:
None
Environment variables:
Not set
global.json file:
Not found
Learn more:
https://aka.ms/dotnet/info
Download .NET:
https://aka.ms/dotnet/download
Microsoft Reviewers: Open in CodeFlow