Handle transient GDI+ ExternalException in SplitContainer.RepaintSplitterRect during display-session transition#14565
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…tterRect during display-session transition
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Pull request overview
This pull request prevents intermittent crashes in WinForms SplitContainer during display-session transitions (e.g., Windows lock/unlock) by handling transient GDI+ failures that can occur when repainting the splitter during layout.
Changes:
- Wrap
SplitContainer.RepaintSplitterRect()immediate GDI+ drawing in atry/catch (ExternalException). - Suppress transient GDI+ repaint failures so layout/painting can recover on subsequent paint cycles.
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ricardobossan
approved these changes
May 28, 2026
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Fixes #14562
Root Cause
SplitContainer.RepaintSplitterRect()performs immediate GDI+ drawing during layout (CreateGraphicsInternal+FillRectangle).During display-session transitions (for example, Windows lock/unlock), the graphics context can become transiently invalid and GDI+ may throw
ExternalException(A generic error occurred in GDI+).This exception was previously unhandled in this path and could bubble up as an unhandled exception.
Proposed changes
SplitContainer.RepaintSplitterRect():try/catch (ExternalException).Customer Impact
SplitContainerRegression?
Risk
Screenshots
Sample project: WinFormsApp5.zip
Before
When a window containing
SplitContaineris opened and the machine is locked before layout completes, unlocking can trigger an unhandled error dialog (“A generic error occurred in GDI+”).After
Under the same lock/unlock timing, users no longer see the GDI+ error dialog and the app does not crash from this path.
The window opens and continues rendering normally after unlock, with no new UI changes in normal scenarios.
Test methodology
Test environment(s)
Microsoft Reviewers: Open in CodeFlow