Fixes #4885. View.GetScheme() falls back gracefully instead of throwing when SchemeName is not found#4886
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tig merged 7 commits intogui-cs:developfrom Apr 8, 2026
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…etScheme()
Add SchemeManager.TryGetScheme() — a non-throwing scheme lookup that safely
handles uninitialized ConfigurationManager and missing Schemes in the current
theme (both cases that GetSchemesForCurrentTheme() throws for).
Refactor View.GetScheme() DefaultAction to use the full fallback chain in all
cases, removing the asymmetry where a SchemeName pointing to a missing scheme
threw KeyNotFoundException while no SchemeName gracefully fell back:
HasScheme (_scheme)
-> Named scheme via TryGetScheme(SchemeName)
-> SuperView.GetScheme()
-> 'Base' scheme
-> Hard-coded 'Base' (guaranteed last resort)
Add Logging.Warning() when SchemeName is set but not found, to aid debugging.
Add tests covering: TryGetScheme happy/sad paths, fallback to SuperView,
fallback to Base, and full chain traversal with missing scheme at every level.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
…k chain - Registers a custom 'CustomHighlight' scheme with TextStyle.Blink on the Default theme, making it visually distinct from built-in schemes - Shows a view with SchemeName = 'CustomHighlight' (found on Default, blinks) - Shows a view with SchemeName = 'NonExistentScheme' (never found, falls back) - Includes a theme selector: switching to a non-Default theme causes 'CustomHighlight' to also fall back, demonstrating both fallback cases live - The warning written to the debug log for missing scheme names is mentioned in the UI Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Excellent!
I effed up on an earlier merge to develop and introduced a bug to UICatalog. I pulled your branch down to review and noticed that. So I fixed it in your branch and pushed that and some code cleanup changes too.
…d didn't test... Refactor style, naming, and shortcut logic for consistency Refactored constant naming and string interpolation in ThemeFallback for clarity and consistency. Improved XML documentation formatting. Updated UICatalogRunnable shortcut key assignment to avoid conflicts and accept ignored keys. Fixed GetScheme logic in View to handle empty SchemeName correctly. Replaced var with explicit types and used collection expressions in tests. Improved lambda formatting and simplified event handler assignments. Applied project code style conventions throughout.
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Pull request overview
Implements a non-throwing scheme resolution path so View.GetScheme() gracefully falls back when SchemeName is missing from the active theme (Fixes #4885), while preserving existing throwing APIs for backwards compatibility.
Changes:
- Added
SchemeManager.TryGetScheme(string, out Scheme?)to safely resolve schemes without exceptions. - Updated
View.GetScheme()to useTryGetSchemeplus a fallback chain (SuperView → theme “Base” → hard-coded “Base”) and emit a warning when falling back. - Added/updated tests and introduced a new UICatalog scenario to demonstrate the fallback behavior live.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 8 comments.
Show a summary per file
| File | Description |
|---|---|
| Tests/UnitTestsParallelizable/ViewBase/Draw/SchemeTests.cs | Adds fallback-chain tests and refactors some locals/types. |
| Tests/UnitTestsParallelizable/Configuration/SourcesManagerTests.cs | Minor test refactors/cleanup unrelated to schemes. |
| Tests/UnitTestsParallelizable/Configuration/SchemeManagerTests.cs | Adds tests for TryGetScheme behavior. |
| Terminal.Gui/ViewBase/View.Drawing.Scheme.cs | Implements GetScheme() fallback chain + warning logging. |
| Terminal.Gui/Configuration/SchemeManager.cs | Adds TryGetScheme API and updates exception docs for GetScheme(string). |
| Examples/UICatalog/UICatalogRunnable.cs | Adjusts unbound F-key selection logic for StatusBar/menu usage. |
| Examples/UICatalog/Scenarios/ThemeFallback.cs | New scenario demonstrating missing-scheme fallback behavior across theme changes. |
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Apr 10, 2026
…g.md Document PR gui-cs#4886 functionality in config.md: - Add 'Custom Schemes for Individual Views' section showing View.SchemeName, SchemeManager.AddScheme(), and JSON config definition of custom schemes - Add 'Scheme Resolution Order' section with Mermaid flowchart of the View.GetScheme() fallback chain (HasScheme -> SchemeName -> SuperView -> Base theme -> hard-coded Base) and priority table - Note SchemeManager.TryGetScheme() as the safe consumer API Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Fixes #4885.
Summary
When
View.SchemeNameis set to a name that doesn't exist in the active theme,View.GetScheme()previously threw aKeyNotFoundException. This PR implements a graceful fallback chain so the view degrades silently instead of crashing.Fallback Chain
If the named scheme is not found, resolution continues through:
SuperView.GetScheme()— inherit from the parent view (recursive)"Base"scheme from the active theme"Base"— always available regardless of config stateA
Logging.Warningis emitted when a fallback occurs so developers can diagnose misconfiguredSchemeNamevalues.Changes
SchemeManager— newTryGetSchememethodcsharp public static bool TryGetScheme(string schemeName, [NotNullWhen(true)] out Scheme? scheme)Fully exception-safe: handles an uninitialised
ConfigurationManagerand a theme with noSchemesproperty, returningfalsein both cases.GetScheme(string)is left unchanged (backward compat — it still throws).View.GetScheme()— use fallback chainReplaced the direct
SchemeManager.GetScheme(SchemeName)call (which throws) withTryGetScheme+ResolveFallbackScheme().UICatalog scenario — Theme Fallback
New demo scenario (
Examples/UICatalog/Scenarios/ThemeFallback.cs) showing:SchemeName = "CustomHighlight"(exists on Default, blinking yellow/blue)SchemeName = "NonExistentScheme"(never exists, always falls back)Tests
7 new tests across two files — all in
UnitTestsParallelizable:SchemeManagerTests.csTryGetSchemehappy path, missing scheme, CM-not-initialisedSchemeTests.csAll 15,163 existing tests pass; no new warnings.