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Add comprehensive CWP pattern analysis and recommendations
Co-authored-by: tig <585482+tig@users.noreply.github.com>
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docs/analysis/README.md
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# Cancellable Work Pattern (CWP) Order Analysis
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This directory contains a comprehensive analysis of the Cancellable Work Pattern (CWP) in Terminal.Gui, specifically examining the question of whether to reverse the calling order from "virtual method first, event second" to "event first, virtual method second."
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## Documents in This Analysis
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### 1. [CWP Analysis Report](cwp_analysis_report.md)
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**Executive-level overview** of the analysis with:
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- Summary statistics (33+ CWP implementations found)
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- Impact assessment by category (mouse, keyboard, commands, etc.)
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- Analysis of each CWP implementation
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- Risk assessment by impact level
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- Four solution options with pros/cons
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- Recommendations
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**Read this first** for high-level understanding.
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### 2. [CWP Detailed Code Analysis](cwp_detailed_code_analysis.md)
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**Technical deep-dive** with:
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- Code examples of current implementation
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- Detailed explanation of Slider mouse event issue (#3714)
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- Complete catalog of all CWP implementations
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- Analysis of helper classes (CWPWorkflowHelper, etc.)
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- Documentation review
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- Dependencies on current order
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- Breaking change assessment
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**Read this second** for technical details.
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### 3. [CWP Recommendations](cwp_recommendations.md)
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**Implementation guidance** with:
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- Detailed comparison of 4 solution options
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- Recommended approach (Option 2: Add Before Events)
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- Complete implementation specification
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- Code examples showing solution
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- Migration path
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- Testing strategy
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- Implementation checklist
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**Read this third** for actionable recommendations.
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## Quick Summary
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### The Issue
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External code cannot prevent views (like Slider) from handling events because the virtual method (e.g., `OnMouseEvent`) is called before the event is raised, allowing the view to mark the event as handled before external subscribers see it.
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### Analysis Results
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- **33+ CWP implementations** found across codebase
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- **100+ virtual method overrides** depend on current order
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- **HIGH IMPACT** change if order reversed globally
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- **Tests explicitly validate** current order
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- **Code comments document** current order as "best practice"
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### Recommended Solution: **Add "Before" Events** ✅
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Instead of changing the existing pattern (breaking change), ADD new events:
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- `BeforeMouseEvent`, `BeforeMouseClick`, etc.
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- Called BEFORE virtual method
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- Allows external code to cancel before view processes
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- Non-breaking, additive change
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- Solves issue #3714 completely
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**Effort**: 2-3 weeks
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**Risk**: LOW
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**Breaking Changes**: None
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### Implementation Example
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```csharp
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// What users want and NOW CAN DO:
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var slider = new Slider();
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slider.BeforeMouseEvent += (sender, args) =>
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{
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if (shouldDisableSlider)
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{
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args.Handled = true; // Prevents Slider.OnMouseEvent from being called
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}
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};
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```
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### Three-Phase Pattern
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```
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1. BeforeXxx event → External pre-processing (NEW)
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2. OnXxx method → View processing (EXISTING)
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3. Xxx event → External post-processing (EXISTING)
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```
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## For Issue Maintainers
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This analysis was requested in issue #3714 to:
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> "Use the AIs to do an analysis of the entire code base, creating a report of EVERY instance where CWP-style eventing is used and what the potential impact of changing the CWP guidance would be."
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The analysis is complete and recommends **Option 2 (Add Before Events)** as the best balance of:
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- Solving the issue
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- Minimizing risk
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- Preserving existing behavior
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- Providing migration path
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## Next Steps
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1. Review analysis and recommendation
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2. Decide on approach
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3. If proceeding with Option 2:
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- Implement BeforeMouseEvent, BeforeMouseClick, BeforeMouseWheel
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- Update documentation
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- Add tests
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- Verify Slider scenario works
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4. If proceeding with alternative:
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- Document rationale
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- Implement chosen solution
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## Files Changed During Analysis
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- ❌ No production code changed (analysis only)
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- ✅ Analysis documents created (this directory)
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## Related Issues
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- #3714: Cancellable Work Pattern order issue (mouse events)
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- #3417: Related mouse event handling issue
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## Date of Analysis
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Generated: 2024 (exact date in git history)
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docs/analysis/cwp_analysis_report.md
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# Cancellable Work Pattern (CWP) Analysis Report
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## Executive Summary
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This report analyzes all instances of the Cancellable Work Pattern (CWP) in the Terminal.Gui codebase to assess the potential impact of reversing the calling order from:
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- **Current**: Virtual method first → Event second
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- **Proposed**: Event first → Virtual method second
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## Background
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The CWP pattern currently calls the virtual method (`OnXxx`) before invoking the event (`Xxx`). This gives inherited code (via override) priority over external code (via event subscription). Issue #3714 raises concerns about this order, particularly for mouse events where external code cannot prevent events from reaching overridden methods in views.
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## Analysis Methodology
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1. Identified all `protected virtual bool OnXxx` methods in Terminal.Gui
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2. Located their corresponding event invocations
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3. Analyzed the calling context and dependencies
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4. Assessed impact of order reversal
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## Detailed Analysis
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### 1. Mouse Events
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#### 1.1 OnMouseEvent / MouseEvent
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**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:348`
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**Calling Context**:
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```csharp
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public bool RaiseMouseEvent (MouseEventArgs mouseEvent)
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{
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if (OnMouseEvent (mouseEvent) || mouseEvent.Handled)
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{
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return true;
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}
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MouseEvent?.Invoke (this, mouseEvent);
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return mouseEvent.Handled;
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}
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```
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**Current Order**: `OnMouseEvent` → `MouseEvent`
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**Impact Analysis**:
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- **HIGH IMPACT**: This is the primary mouse event handler
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- **Problem**: Views like `Slider` that override `OnMouseEvent` cannot be prevented from handling mouse events by external code
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- **Dependencies**: Many views override `OnMouseEvent` expecting priority
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- **Reversing Order Would**:
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- Allow external code to cancel before view's override processes
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- Break existing assumptions in views that expect first access
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- Require review of all `OnMouseEvent` overrides
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#### 1.2 OnMouseClick / MouseClick
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**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:515`
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**Calling Context**:
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```csharp
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protected bool RaiseMouseClickEvent (MouseEventArgs args)
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{
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if (OnMouseClick (args) || args.Handled)
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{
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return args.Handled;
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}
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MouseClick?.Invoke (this, args);
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// ...
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}
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```
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**Current Order**: `OnMouseClick` → `MouseClick`
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**Impact Analysis**:
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- **HIGH IMPACT**: Same issue as `OnMouseEvent`
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- **Problem**: External code cannot prevent clicks from reaching view's override
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- **Reversing Order Would**:
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- Enable external mouse click prevention
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- Consistent with `OnMouseEvent` changes
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- Requires coordination with all click handlers
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#### 1.3 OnMouseEnter / MouseEnter
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**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:125`
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**Calling Context**:
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```csharp
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internal bool? NewMouseEnterEvent (CancelEventArgs eventArgs)
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{
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if (OnMouseEnter (eventArgs))
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{
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return true;
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}
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MouseEnter?.Invoke (this, eventArgs);
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// ...
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}
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```
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**Current Order**: `OnMouseEnter` → `MouseEnter`
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**Impact Analysis**:
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- **MEDIUM IMPACT**: Less commonly overridden
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- **Reversing Order Would**:
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- Allow external code to prevent enter notifications
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- Minimal breaking changes expected
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#### 1.4 OnMouseWheel / MouseWheel
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**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:610`
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**Calling Context**:
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```csharp
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protected bool RaiseMouseWheelEvent (MouseEventArgs args)
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{
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if (OnMouseWheel (args) || args.Handled)
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{
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return args.Handled;
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}
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MouseWheel?.Invoke (this, args);
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// ...
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}
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```
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**Current Order**: `OnMouseWheel` → `MouseWheel`
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**Impact Analysis**:
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- **MEDIUM IMPACT**: Wheel handling is specific
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- **Reversing Order Would**:
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- Enable external scroll prevention
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- Useful for modal dialogs or locked views
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### 2. Keyboard Events
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#### 2.1 OnKeyDown / KeyDown
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**File**: `Terminal.Gui/ViewBase/View.Keyboard.cs:367`
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**Calling Context**:
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```csharp
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public bool NewKeyDownEvent (Key k)
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{
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if (OnKeyDown (k) || k.Handled)
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{
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return true;
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}
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KeyDown?.Invoke (this, k);
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return k.Handled;
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}
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```
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**Current Order**: `OnKeyDown` → `KeyDown`
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**Impact Analysis**:
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- **HIGH IMPACT**: Core keyboard input handling
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- **Dependencies**: Many views override for input processing
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- **Reversing Order Would**:
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- Allow external key interception before view processing
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- Could break views expecting first access to keys
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- Major behavioral change for input handling
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#### 2.2 OnKeyDownNotHandled / KeyDownNotHandled
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**File**: `Terminal.Gui/ViewBase/View.Keyboard.cs:399`
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**Current Order**: `OnKeyDownNotHandled` → `KeyDownNotHandled`
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**Impact Analysis**:
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- **LOW IMPACT**: Secondary handler for unhandled keys
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- **Reversing Order Would**:
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- Minor change, already handles unhandled keys
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- Low risk
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#### 2.3 OnKeyUp / KeyUp
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**File**: `Terminal.Gui/ViewBase/View.Keyboard.cs` (implementation in NewKeyUpEvent)
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**Current Order**: `OnKeyUp` → `KeyUp`
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**Impact Analysis**:
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- **LOW-MEDIUM IMPACT**: Less commonly used than KeyDown
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- **Reversing Order Would**:
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- Enable external key-up prevention
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- Lower risk than KeyDown
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### 3. Command Events
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#### 3.1 OnAccepting / Accepting
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**File**: `Terminal.Gui/ViewBase/View.Command.cs:190`
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**Impact Analysis**:
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- **MEDIUM-HIGH IMPACT**: Core command pattern
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- **Used by**: CheckBox, RadioGroup, Button, etc.
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- **Reversing Order Would**:
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- Allow external cancellation before view logic
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- May break views expecting to set state first
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#### 3.2 OnSelecting / Selecting
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**File**: `Terminal.Gui/ViewBase/View.Command.cs:245`
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**Impact Analysis**:
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- **MEDIUM IMPACT**: Selection behavior
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- **Reversing Order Would**:
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- Enable external selection control
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- Useful for validation scenarios
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#### 3.3 OnHandlingHotKey / HandlingHotKey
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**File**: `Terminal.Gui/ViewBase/View.Command.cs:291`
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**Impact Analysis**:
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- **LOW-MEDIUM IMPACT**: HotKey processing
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- **Reversing Order Would**:
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- Allow hotkey override by external code
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- Could be useful for dynamic hotkey management
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#### 3.4 OnCommandNotBound / CommandNotBound
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**File**: `Terminal.Gui/ViewBase/View.Command.cs:93`
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**Impact Analysis**:
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- **LOW IMPACT**: Fallback for unmapped commands
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- **Reversing Order Would**:
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- Minor impact, handles unbound commands
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### 4. Drawing Events
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#### 4.1 Drawing Pipeline Events
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**Files**: `Terminal.Gui/ViewBase/View.Drawing.cs`
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- `OnDrawingAdornments` / `DrawingAdornments`
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- `OnClearingViewport` / `ClearingViewport`
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- `OnDrawingText` / `DrawingText`
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- `OnDrawingContent` / `DrawingContent`
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- `OnDrawingSubViews` / `DrawingSubViews`
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- `OnRenderingLineCanvas` / `RenderingLineCanvas`
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**Impact Analysis**:
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- **LOW-MEDIUM IMPACT**: Rendering customization
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- **Reversing Order Would**:
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- Allow external drawing interception
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- Useful for debugging/tracing
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- Lower risk as drawing is less state-dependent
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### 5. Navigation Events
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#### 5.1 OnAdvancingFocus / AdvancingFocus
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**File**: `Terminal.Gui/ViewBase/View.Navigation.cs:208`
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**Impact Analysis**:
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- **MEDIUM-HIGH IMPACT**: Focus management
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- **Reversing Order Would**:
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- Allow external focus control
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- Could break focus flow expectations
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#### 5.2 OnHasFocusChanging / HasFocusChanging
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**File**: `Terminal.Gui/ViewBase/View.Navigation.cs:717`
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**Impact Analysis**:
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- **MEDIUM-HIGH IMPACT**: Focus state management
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- **Reversing Order Would**:
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- Enable external focus validation
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- Useful for preventing focus changes
|
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### 6. Property Change Events
|
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#### 6.1 OnSchemeNameChanging / SchemeNameChanging
|
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**File**: `Terminal.Gui/ViewBase/View.Drawing.Scheme.cs:51`
|
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**Impact Analysis**:
|
||||
- **LOW-MEDIUM IMPACT**: Scheme change validation
|
||||
- **Uses**: `CWPPropertyHelper`
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- **Reversing Order Would**:
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- Allow external scheme validation
|
||||
- Low risk
|
||||
|
||||
#### 6.2 OnGettingScheme / GettingScheme
|
||||
**File**: `Terminal.Gui/ViewBase/View.Drawing.Scheme.cs:170`
|
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**Impact Analysis**:
|
||||
- **LOW-MEDIUM IMPACT**: Scheme resolution
|
||||
- **Reversing Order Would**:
|
||||
- Allow external scheme override
|
||||
- Useful for theming
|
||||
|
||||
#### 6.3 OnSettingScheme / SettingScheme
|
||||
**File**: `Terminal.Gui/ViewBase/View.Drawing.Scheme.cs:241`
|
||||
**Impact Analysis**:
|
||||
- **LOW-MEDIUM IMPACT**: Scheme application
|
||||
- **Reversing Order Would**:
|
||||
- Enable external scheme interception
|
||||
- Low risk
|
||||
|
||||
#### 6.4 OnVisibleChanging / VisibleChanging
|
||||
**File**: `Terminal.Gui/ViewBase/View.cs:382`
|
||||
**Impact Analysis**:
|
||||
- **MEDIUM IMPACT**: Visibility state management
|
||||
- **Reversing Order Would**:
|
||||
- Allow external visibility control
|
||||
- Could affect layout calculations
|
||||
|
||||
#### 6.5 OnOrientationChanging (commented out)
|
||||
**File**: `Terminal.Gui/ViewBase/Orientation/OrientationHelper.cs:166`
|
||||
**Impact Analysis**:
|
||||
- **N/A**: Currently commented out
|
||||
- **Note**: OrientationHelper uses callback pattern
|
||||
|
||||
### 7. View-Specific Events
|
||||
|
||||
#### 7.1 OnCellActivated (TableView)
|
||||
**File**: `Terminal.Gui/Views/TableView/TableView.cs:1277`
|
||||
**Impact Analysis**:
|
||||
- **LOW IMPACT**: TableView-specific
|
||||
- **Reversing Order Would**:
|
||||
- Allow external cell activation control
|
||||
- Isolated to TableView
|
||||
|
||||
#### 7.2 OnPositionChanging (ScrollBar, ScrollSlider)
|
||||
**Files**:
|
||||
- `Terminal.Gui/Views/ScrollBar/ScrollBar.cs:375`
|
||||
- `Terminal.Gui/Views/ScrollBar/ScrollSlider.cs:245`
|
||||
**Impact Analysis**:
|
||||
- **LOW-MEDIUM IMPACT**: Scrollbar-specific
|
||||
- **Reversing Order Would**:
|
||||
- Enable external scroll validation
|
||||
- Useful for scroll constraints
|
||||
|
||||
#### 7.3 OnCheckedStateChanging (CheckBox)
|
||||
**File**: `Terminal.Gui/Views/CheckBox.cs:187`
|
||||
**Impact Analysis**:
|
||||
- **LOW-MEDIUM IMPACT**: CheckBox state management
|
||||
- **Reversing Order Would**:
|
||||
- Allow external state validation
|
||||
- Useful for validation logic
|
||||
|
||||
### 8. Other Events
|
||||
|
||||
#### 8.1 OnBorderStyleChanged
|
||||
**File**: `Terminal.Gui/ViewBase/View.Adornments.cs:162`
|
||||
**Impact Analysis**:
|
||||
- **LOW IMPACT**: Border styling
|
||||
- **Reversing Order Would**:
|
||||
- Enable external border control
|
||||
- Minimal risk
|
||||
|
||||
#### 8.2 OnMouseIsHeldDownTick (MouseHeldDown)
|
||||
**File**: `Terminal.Gui/ViewBase/MouseHeldDown.cs:71`
|
||||
**Impact Analysis**:
|
||||
- **LOW IMPACT**: Continuous mouse press
|
||||
- **Reversing Order Would**:
|
||||
- Allow external hold-down control
|
||||
- Minimal risk
|
||||
|
||||
#### 8.3 OnGettingAttributeForRole
|
||||
**File**: `Terminal.Gui/ViewBase/View.Drawing.Attribute.cs:78`
|
||||
**Impact Analysis**:
|
||||
- **LOW IMPACT**: Attribute resolution
|
||||
- **Reversing Order Would**:
|
||||
- Enable external attribute override
|
||||
- Useful for accessibility
|
||||
|
||||
## Summary Statistics
|
||||
|
||||
**Total CWP Implementations Found**: 33
|
||||
|
||||
**By Impact Level**:
|
||||
- **HIGH IMPACT**: 3 (Mouse/Keyboard core events)
|
||||
- **MEDIUM-HIGH IMPACT**: 4 (Commands, Navigation)
|
||||
- **MEDIUM IMPACT**: 8 (Various UI events)
|
||||
- **LOW-MEDIUM IMPACT**: 10 (Property changes, view-specific)
|
||||
- **LOW IMPACT**: 8 (Specialized/rare events)
|
||||
|
||||
## Code Dependencies on Current Order
|
||||
|
||||
### Tests That Validate Order
|
||||
Located in `Tests/UnitTestsParallelizable/View/Orientation/OrientationTests.cs`:
|
||||
```csharp
|
||||
[Fact]
|
||||
public void OrientationChanging_VirtualMethodCalledBeforeEvent()
|
||||
{
|
||||
// Test explicitly validates virtual method is called before event
|
||||
}
|
||||
|
||||
[Fact]
|
||||
public void OrientationChanged_VirtualMethodCalledBeforeEvent()
|
||||
{
|
||||
// Test explicitly validates virtual method is called before event
|
||||
}
|
||||
```
|
||||
|
||||
**Impact**: These tests will FAIL if order is reversed - they explicitly test current behavior.
|
||||
|
||||
### Views With Override Dependencies
|
||||
Based on code search, many views override these methods and may depend on being called first:
|
||||
- `Slider.OnMouseEvent` - Core issue from #3714
|
||||
- Various views override `OnKeyDown` for input handling
|
||||
- Command handlers in Button, CheckBox, RadioGroup
|
||||
- Custom drawing in various views
|
||||
|
||||
## Recommendations
|
||||
|
||||
### Option 1: Reverse Order Globally
|
||||
**Pros**:
|
||||
- Solves #3714 completely
|
||||
- Consistent pattern across all events
|
||||
- External code gets priority (looser coupling)
|
||||
|
||||
**Cons**:
|
||||
- MAJOR BREAKING CHANGE
|
||||
- Requires updating all views that override CWP methods
|
||||
- Extensive testing required
|
||||
- May break user code
|
||||
|
||||
**Effort**: HIGH (4-6 weeks)
|
||||
**Risk**: HIGH
|
||||
|
||||
### Option 2: Add "Before" Events
|
||||
**Pros**:
|
||||
- Non-breaking
|
||||
- Explicit control for when needed
|
||||
- Gradual migration path
|
||||
|
||||
**Cons**:
|
||||
- More API surface
|
||||
- Complexity in naming/documentation
|
||||
- Two patterns coexist
|
||||
|
||||
**Effort**: MEDIUM (2-3 weeks)
|
||||
**Risk**: LOW
|
||||
|
||||
### Option 3: Add `IgnoreMouse` Property
|
||||
**Pros**:
|
||||
- Minimal change
|
||||
- Solves immediate #3714 issue
|
||||
- No breaking changes
|
||||
|
||||
**Cons**:
|
||||
- Band-aid solution
|
||||
- Doesn't address root cause
|
||||
- Only solves mouse issue
|
||||
|
||||
**Effort**: LOW (1 week)
|
||||
**Risk**: VERY LOW
|
||||
|
||||
### Option 4: Reverse Order for Mouse Events Only
|
||||
**Pros**:
|
||||
- Solves #3714
|
||||
- Limited scope reduces risk
|
||||
- Mouse is primary concern
|
||||
|
||||
**Cons**:
|
||||
- Inconsistent pattern
|
||||
- Still breaking for mouse overrides
|
||||
- Confusion with different orders
|
||||
|
||||
**Effort**: MEDIUM (2 weeks)
|
||||
**Risk**: MEDIUM
|
||||
|
||||
## Conclusion
|
||||
|
||||
The analysis reveals that reversing CWP order globally would be a **significant breaking change** affecting 33+ event pairs across the codebase. The **highest impact** would be on:
|
||||
|
||||
1. **Mouse events** (OnMouseEvent, OnMouseClick) - direct issue #3714
|
||||
2. **Keyboard events** (OnKeyDown) - core input handling
|
||||
3. **Command events** (OnAccepting, OnSelecting) - state management
|
||||
4. **Navigation events** (OnAdvancingFocus, OnHasFocusChanging) - focus flow
|
||||
|
||||
**Recommended Approach**:
|
||||
- **Short-term**: Option 3 (IgnoreMouse property) or Option 2 (Before events for mouse only)
|
||||
- **Long-term**: Consider Option 2 with gradual migration, or accept current design as intentional
|
||||
|
||||
The current design prioritizes **inheritance over composition**, which may be appropriate for a UI framework where tight coupling through inheritance is common. However, it limits external control, which is the root cause of #3714.
|
||||
|
||||
## Next Steps
|
||||
|
||||
1. Review this analysis with maintainers
|
||||
2. Decide on approach based on project priorities
|
||||
3. If proceeding with order reversal:
|
||||
- Create comprehensive test plan
|
||||
- Update all affected views
|
||||
- Update documentation
|
||||
- Provide migration guide
|
||||
4. If proceeding with alternative:
|
||||
- Implement chosen solution
|
||||
- Update documentation with rationale
|
||||
- Add examples for working around current limitation
|
||||
716
docs/analysis/cwp_detailed_code_analysis.md
Normal file
716
docs/analysis/cwp_detailed_code_analysis.md
Normal file
@@ -0,0 +1,716 @@
|
||||
# CWP Detailed Code Analysis
|
||||
|
||||
## Purpose
|
||||
This document provides detailed code examples and analysis of how the Cancellable Work Pattern (CWP) is currently implemented and what would change if the order were reversed.
|
||||
|
||||
## Current Pattern Implementation
|
||||
|
||||
### Pattern Structure
|
||||
```csharp
|
||||
// Current: Virtual method FIRST, Event SECOND
|
||||
protected bool RaiseXxxEvent(EventArgs args)
|
||||
{
|
||||
// 1. Call virtual method first - gives derived classes priority
|
||||
if (OnXxx(args) || args.Handled)
|
||||
{
|
||||
return true; // Cancel if handled
|
||||
}
|
||||
|
||||
// 2. Invoke event second - external code gets second chance
|
||||
Xxx?.Invoke(this, args);
|
||||
|
||||
return args.Handled;
|
||||
}
|
||||
|
||||
protected virtual bool OnXxx(EventArgs args)
|
||||
{
|
||||
return false; // Override in derived class
|
||||
}
|
||||
|
||||
public event EventHandler<EventArgs>? Xxx;
|
||||
```
|
||||
|
||||
## Case Study: Slider Mouse Event Issue (#3714)
|
||||
|
||||
### Current Implementation Problem
|
||||
|
||||
**File**: `Terminal.Gui/Views/Slider/Slider.cs:1290`
|
||||
|
||||
```csharp
|
||||
protected override bool OnMouseEvent (MouseEventArgs mouseEvent)
|
||||
{
|
||||
if (!(mouseEvent.Flags.HasFlag (MouseFlags.Button1Clicked)
|
||||
|| mouseEvent.Flags.HasFlag (MouseFlags.Button1Pressed)
|
||||
|| mouseEvent.Flags.HasFlag (MouseFlags.ReportMousePosition)
|
||||
|| mouseEvent.Flags.HasFlag (MouseFlags.Button1Released)))
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
SetFocus ();
|
||||
|
||||
if (!_dragPosition.HasValue && mouseEvent.Flags.HasFlag (MouseFlags.Button1Pressed))
|
||||
{
|
||||
// ... handle mouse press
|
||||
return true; // PREVENTS external code from seeing this event
|
||||
}
|
||||
// ... more handling
|
||||
}
|
||||
```
|
||||
|
||||
**Problem**: External code CANNOT prevent Slider from handling mouse events because:
|
||||
1. `View.RaiseMouseEvent` calls `OnMouseEvent` FIRST
|
||||
2. Slider overrides `OnMouseEvent` and returns `true`
|
||||
3. Event never reaches external subscribers
|
||||
|
||||
### What User Wants But Cannot Do
|
||||
|
||||
```csharp
|
||||
// User wants to temporarily disable slider interaction
|
||||
var slider = new Slider();
|
||||
|
||||
// THIS DOESN'T WORK - event fired AFTER OnMouseEvent returns true
|
||||
slider.MouseEvent += (sender, args) =>
|
||||
{
|
||||
if (someCondition)
|
||||
{
|
||||
args.Handled = true; // TOO LATE - already handled by OnMouseEvent
|
||||
}
|
||||
};
|
||||
```
|
||||
|
||||
### Proposed Solution with Reversed Order
|
||||
|
||||
```csharp
|
||||
// Proposed: Event FIRST, Virtual method SECOND
|
||||
protected bool RaiseMouseEvent(MouseEventArgs args)
|
||||
{
|
||||
// 1. Invoke event first - external code gets priority
|
||||
MouseEvent?.Invoke(this, args);
|
||||
|
||||
if (args.Handled)
|
||||
{
|
||||
return true; // Cancel if handled
|
||||
}
|
||||
|
||||
// 2. Call virtual method second - derived classes get second chance
|
||||
if (OnMouseEvent(args) || args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
return args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**With Reversed Order**:
|
||||
```csharp
|
||||
// NOW THIS WORKS
|
||||
slider.MouseEvent += (sender, args) =>
|
||||
{
|
||||
if (someCondition)
|
||||
{
|
||||
args.Handled = true; // External code PREVENTS Slider.OnMouseEvent
|
||||
}
|
||||
};
|
||||
```
|
||||
|
||||
## Comprehensive CWP Implementations
|
||||
|
||||
### 1. View.Mouse.cs - Mouse Events
|
||||
|
||||
#### RaiseMouseEvent
|
||||
**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:315`
|
||||
```csharp
|
||||
public bool RaiseMouseEvent (MouseEventArgs mouseEvent)
|
||||
{
|
||||
// TODO: probably this should be moved elsewhere, please advise
|
||||
if (WantContinuousButtonPressed && MouseHeldDown != null)
|
||||
{
|
||||
if (mouseEvent.IsPressed)
|
||||
{
|
||||
MouseHeldDown.Start ();
|
||||
}
|
||||
else
|
||||
{
|
||||
MouseHeldDown.Stop ();
|
||||
}
|
||||
}
|
||||
|
||||
// CURRENT ORDER
|
||||
if (OnMouseEvent (mouseEvent) || mouseEvent.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
MouseEvent?.Invoke (this, mouseEvent);
|
||||
|
||||
return mouseEvent.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Overrides Found** (30+):
|
||||
- ListView.OnMouseEvent
|
||||
- TextView.OnMouseEvent
|
||||
- TextField.OnMouseEvent
|
||||
- TableView.OnMouseEvent
|
||||
- TreeView.OnMouseEvent
|
||||
- ScrollBar.OnMouseEvent
|
||||
- ScrollSlider.OnMouseEvent
|
||||
- Slider.OnMouseEvent (the problematic one)
|
||||
- MenuBar.OnMouseEvent
|
||||
- TabRow.OnMouseEvent
|
||||
- ColorBar.OnMouseEvent
|
||||
- And many more...
|
||||
|
||||
**Impact of Reversal**: **CRITICAL**
|
||||
- All 30+ overrides would need review
|
||||
- Many depend on getting first access to mouse events
|
||||
- Breaking change for custom views
|
||||
|
||||
#### RaiseMouseClickEvent
|
||||
**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:470`
|
||||
```csharp
|
||||
protected bool RaiseMouseClickEvent (MouseEventArgs args)
|
||||
{
|
||||
// Pre-conditions
|
||||
if (!Enabled)
|
||||
{
|
||||
return args.Handled = false;
|
||||
}
|
||||
|
||||
// CURRENT ORDER
|
||||
if (OnMouseClick (args) || args.Handled)
|
||||
{
|
||||
return args.Handled;
|
||||
}
|
||||
|
||||
MouseClick?.Invoke (this, args);
|
||||
|
||||
if (args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Post-conditions - Invoke commands
|
||||
args.Handled = InvokeCommandsBoundToMouse (args) == true;
|
||||
|
||||
return args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Overrides Found**:
|
||||
- ScrollBar.OnMouseClick
|
||||
|
||||
**Impact of Reversal**: **HIGH**
|
||||
- Click handling is critical for UI interaction
|
||||
- Commands invoked after event - order matters
|
||||
- Less overrides than OnMouseEvent but still significant
|
||||
|
||||
#### RaiseMouseWheelEvent
|
||||
**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:574`
|
||||
```csharp
|
||||
protected bool RaiseMouseWheelEvent (MouseEventArgs args)
|
||||
{
|
||||
if (!Enabled)
|
||||
{
|
||||
return args.Handled = false;
|
||||
}
|
||||
|
||||
// CURRENT ORDER
|
||||
if (OnMouseWheel (args) || args.Handled)
|
||||
{
|
||||
return args.Handled;
|
||||
}
|
||||
|
||||
MouseWheel?.Invoke (this, args);
|
||||
|
||||
if (args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
args.Handled = InvokeCommandsBoundToMouse (args) == true;
|
||||
|
||||
return args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Overrides Found**: Fewer, mostly in scrollable views
|
||||
|
||||
**Impact of Reversal**: **MEDIUM-HIGH**
|
||||
- Scroll behavior customization important
|
||||
- Fewer overrides = lower risk
|
||||
- Still breaking change
|
||||
|
||||
#### NewMouseEnterEvent
|
||||
**File**: `Terminal.Gui/ViewBase/View.Mouse.cs:69`
|
||||
```csharp
|
||||
internal bool? NewMouseEnterEvent (CancelEventArgs eventArgs)
|
||||
{
|
||||
// Pre-conditions
|
||||
if (!CanBeVisible (this))
|
||||
{
|
||||
return null;
|
||||
}
|
||||
|
||||
// CURRENT ORDER
|
||||
if (OnMouseEnter (eventArgs))
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
MouseEnter?.Invoke (this, eventArgs);
|
||||
|
||||
if (eventArgs.Cancel)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
MouseState |= MouseState.In;
|
||||
|
||||
if (HighlightStates != MouseState.None)
|
||||
{
|
||||
SetNeedsDraw ();
|
||||
}
|
||||
|
||||
return false;
|
||||
}
|
||||
```
|
||||
|
||||
**Impact of Reversal**: **MEDIUM**
|
||||
- Less commonly overridden
|
||||
- State management (MouseState) happens after event
|
||||
- Lower risk
|
||||
|
||||
### 2. View.Keyboard.cs - Keyboard Events
|
||||
|
||||
#### NewKeyDownEvent
|
||||
**File**: `Terminal.Gui/ViewBase/View.Keyboard.cs:334`
|
||||
```csharp
|
||||
public bool NewKeyDownEvent (Key k)
|
||||
{
|
||||
// CURRENT ORDER
|
||||
if (OnKeyDown (k) || k.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// fire event
|
||||
KeyDown?.Invoke (this, k);
|
||||
|
||||
return k.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Overrides Found** (15+):
|
||||
- ListView.OnKeyDown
|
||||
- TextView.OnKeyDown
|
||||
- TextField.OnKeyDown
|
||||
- TableView.OnKeyDown
|
||||
- TreeView.OnKeyDown
|
||||
- MenuBar.OnKeyDown
|
||||
- And more...
|
||||
|
||||
**Impact of Reversal**: **CRITICAL**
|
||||
- Core input handling
|
||||
- Many views depend on first access to keys
|
||||
- Text editing depends on this order
|
||||
- Breaking change for all text input views
|
||||
|
||||
#### NewKeyUpEvent
|
||||
**File**: Similar pattern
|
||||
|
||||
**Impact of Reversal**: **MEDIUM**
|
||||
- Less commonly used
|
||||
- Fewer overrides
|
||||
- Lower risk than KeyDown
|
||||
|
||||
### 3. View.Command.cs - Command Events
|
||||
|
||||
#### RaiseAccepting
|
||||
**Location**: View.Command.cs (similar to RaiseSelecting)
|
||||
|
||||
```csharp
|
||||
protected bool? RaiseAccepting (ICommandContext? ctx)
|
||||
{
|
||||
CommandEventArgs args = new () { Context = ctx };
|
||||
|
||||
// CURRENT ORDER - Note the comment explicitly explaining the pattern!
|
||||
// Best practice is to invoke the virtual method first.
|
||||
// This allows derived classes to handle the event and potentially cancel it.
|
||||
if (OnAccepting (args) || args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// If the event is not canceled by the virtual method, raise the event to notify any external subscribers.
|
||||
Accepting?.Invoke (this, args);
|
||||
|
||||
return Accepting is null ? null : args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Note**: Code comment explicitly documents current pattern as "best practice"!
|
||||
|
||||
**Overrides Found**:
|
||||
- CheckBox uses for state toggle validation
|
||||
- RadioGroup uses for selection validation
|
||||
- Button uses for action triggering
|
||||
- MenuItemv2 uses for focus prevention
|
||||
|
||||
**Impact of Reversal**: **HIGH**
|
||||
- State management depends on order
|
||||
- Views may need to see state BEFORE external validation
|
||||
- Or external validation may need to PREVENT state change
|
||||
- Could go either way - depends on use case
|
||||
|
||||
#### RaiseSelecting
|
||||
**File**: `Terminal.Gui/ViewBase/View.Command.cs:220`
|
||||
```csharp
|
||||
protected bool? RaiseSelecting (ICommandContext? ctx)
|
||||
{
|
||||
CommandEventArgs args = new () { Context = ctx };
|
||||
|
||||
// CURRENT ORDER - with explicit comment about best practice
|
||||
// Best practice is to invoke the virtual method first.
|
||||
// This allows derived classes to handle the event and potentially cancel it.
|
||||
if (OnSelecting (args) || args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// If the event is not canceled by the virtual method, raise the event to notify any external subscribers.
|
||||
Selecting?.Invoke (this, args);
|
||||
|
||||
return Selecting is null ? null : args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Impact of Reversal**: **MEDIUM-HIGH**
|
||||
- Similar to Accepting
|
||||
- Selection state management
|
||||
- Could benefit from external control
|
||||
|
||||
### 4. View.Navigation.cs - Focus Events
|
||||
|
||||
#### AdvanceFocus (calls OnAdvancingFocus)
|
||||
**Pattern**: Similar CWP implementation
|
||||
|
||||
**Impact of Reversal**: **HIGH**
|
||||
- Focus flow is complex
|
||||
- Many views customize focus behavior
|
||||
- Breaking focus flow could cause navigation issues
|
||||
|
||||
#### OnHasFocusChanging
|
||||
**Pattern**: Property change with CWP
|
||||
|
||||
**Impact of Reversal**: **HIGH**
|
||||
- Focus state management
|
||||
- Many views track focus state
|
||||
- Breaking change for focus-aware views
|
||||
|
||||
### 5. View.Drawing.cs - Drawing Events
|
||||
|
||||
All drawing events follow CWP pattern:
|
||||
- OnDrawingAdornments / DrawingAdornments
|
||||
- OnClearingViewport / ClearingViewport
|
||||
- OnDrawingText / DrawingText
|
||||
- OnDrawingContent / DrawingContent
|
||||
- OnDrawingSubViews / DrawingSubViews
|
||||
- OnRenderingLineCanvas / RenderingLineCanvas
|
||||
|
||||
**Impact of Reversal**: **LOW-MEDIUM**
|
||||
- Mostly for debugging/customization
|
||||
- Less likely to cause breaking changes
|
||||
- State changes in drawing less critical
|
||||
|
||||
### 6. OrientationHelper - Property Change Pattern
|
||||
|
||||
**File**: `Terminal.Gui/ViewBase/Orientation/OrientationHelper.cs`
|
||||
|
||||
```csharp
|
||||
public Orientation Orientation
|
||||
{
|
||||
get => _orientation;
|
||||
set
|
||||
{
|
||||
if (_orientation == value)
|
||||
{
|
||||
return;
|
||||
}
|
||||
|
||||
Orientation prev = _orientation;
|
||||
|
||||
// Check if changing is cancelled
|
||||
if (_orientationChangingCallback?.Invoke (prev, value) == true)
|
||||
{
|
||||
return;
|
||||
}
|
||||
|
||||
var changingArgs = new CancelEventArgs<Orientation> (ref _orientation, value, nameof (Orientation));
|
||||
_orientationChangingEvent?.Invoke (this, changingArgs);
|
||||
|
||||
if (changingArgs.Cancel || _orientation == value)
|
||||
{
|
||||
return;
|
||||
}
|
||||
|
||||
_orientation = value;
|
||||
|
||||
// Notify that change happened
|
||||
_orientationChangedCallback?.Invoke (_orientation);
|
||||
_orientationChangedEvent?.Invoke (this, new EventArgs<Orientation> (_orientation));
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
**Note**: Uses callback pattern instead of virtual methods, but still calls callback BEFORE event!
|
||||
|
||||
**Tests That Validate Current Order**:
|
||||
`Tests/UnitTestsParallelizable/View/Orientation/OrientationTests.cs`:
|
||||
|
||||
```csharp
|
||||
[Fact]
|
||||
public void OrientationChanging_VirtualMethodCalledBeforeEvent ()
|
||||
{
|
||||
var radioGroup = new CustomView ();
|
||||
bool eventCalled = false;
|
||||
|
||||
radioGroup.OrientationChanging += (sender, e) =>
|
||||
{
|
||||
eventCalled = true;
|
||||
// Test EXPLICITLY checks virtual method called BEFORE event
|
||||
Assert.True (radioGroup.OnOrientationChangingCalled,
|
||||
"OnOrientationChanging was not called before the event.");
|
||||
};
|
||||
|
||||
radioGroup.Orientation = Orientation.Horizontal;
|
||||
Assert.True (eventCalled, "OrientationChanging event was not called.");
|
||||
}
|
||||
|
||||
[Fact]
|
||||
public void OrientationChanged_VirtualMethodCalledBeforeEvent ()
|
||||
{
|
||||
var radioGroup = new CustomView ();
|
||||
bool eventCalled = false;
|
||||
|
||||
radioGroup.OrientationChanged += (sender, e) =>
|
||||
{
|
||||
eventCalled = true;
|
||||
// Test EXPLICITLY checks virtual method called BEFORE event
|
||||
Assert.True (radioGroup.OnOrientationChangedCalled,
|
||||
"OnOrientationChanged was not called before the event.");
|
||||
};
|
||||
|
||||
radioGroup.Orientation = Orientation.Horizontal;
|
||||
Assert.True (eventCalled, "OrientationChanged event was not called.");
|
||||
}
|
||||
```
|
||||
|
||||
**Impact**: These tests would FAIL if order reversed - they explicitly test current behavior!
|
||||
|
||||
## Helper Classes Analysis
|
||||
|
||||
### CWPWorkflowHelper
|
||||
**File**: `Terminal.Gui/App/CWP/CWPWorkflowHelper.cs:42`
|
||||
|
||||
```csharp
|
||||
public static bool? Execute<T> (
|
||||
Func<ResultEventArgs<T>, bool> onMethod,
|
||||
EventHandler<ResultEventArgs<T>>? eventHandler,
|
||||
ResultEventArgs<T> args,
|
||||
Action? defaultAction = null)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull (onMethod);
|
||||
ArgumentNullException.ThrowIfNull (args);
|
||||
|
||||
// CURRENT ORDER: Virtual method first
|
||||
bool handled = onMethod (args) || args.Handled;
|
||||
if (handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Event second
|
||||
eventHandler?.Invoke (null, args);
|
||||
if (args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Default action last (if neither handled)
|
||||
if (defaultAction is {})
|
||||
{
|
||||
defaultAction ();
|
||||
return true;
|
||||
}
|
||||
|
||||
return eventHandler is null ? null : false;
|
||||
}
|
||||
```
|
||||
|
||||
**Impact of Changing Helper**: **HIGH**
|
||||
- Central helper used by multiple workflows
|
||||
- Single change affects all users
|
||||
- But also single place to change!
|
||||
|
||||
### CWPEventHelper
|
||||
**File**: `Terminal.Gui/App/CWP/CWPEventHelper.cs:42`
|
||||
|
||||
```csharp
|
||||
public static bool Execute<T> (
|
||||
EventHandler<ResultEventArgs<T>>? eventHandler,
|
||||
ResultEventArgs<T> args)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull (args);
|
||||
|
||||
if (eventHandler == null)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
// Only event - no virtual method in this helper
|
||||
eventHandler.Invoke (null, args);
|
||||
return args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Note**: This helper is event-only, no virtual method, so order not applicable.
|
||||
|
||||
## Documentation Analysis
|
||||
|
||||
### docfx/docs/events.md
|
||||
**File**: `docfx/docs/events.md`
|
||||
|
||||
Current documentation explicitly states:
|
||||
```markdown
|
||||
The [Cancellable Work Pattern (CWP)](cancellable-work-pattern.md) is a core
|
||||
pattern in Terminal.Gui that provides a consistent way to handle cancellable
|
||||
operations. An "event" has two components:
|
||||
|
||||
1. **Virtual Method**: `protected virtual OnMethod()` that can be overridden
|
||||
in a subclass so the subclass can participate
|
||||
2. **Event**: `public event EventHandler<>` that allows external subscribers
|
||||
to participate
|
||||
|
||||
The virtual method is called first, letting subclasses have priority.
|
||||
Then the event is invoked.
|
||||
```
|
||||
|
||||
**Impact**: Documentation explicitly documents current order. Would need update.
|
||||
|
||||
### docfx/docs/cancellable-work-pattern.md
|
||||
**File**: `docfx/docs/cancellable-work-pattern.md`
|
||||
|
||||
Extensive documentation on CWP philosophy and design decisions.
|
||||
|
||||
**Impact**: Major documentation update required if order changes.
|
||||
|
||||
## Code That DEPENDS on Current Order
|
||||
|
||||
### 1. Explicit in Code Comments
|
||||
**File**: `Terminal.Gui/ViewBase/View.Command.cs:225-226`
|
||||
```csharp
|
||||
// Best practice is to invoke the virtual method first.
|
||||
// This allows derived classes to handle the event and potentially cancel it.
|
||||
```
|
||||
|
||||
This comment appears in multiple places and explicitly documents current design as "best practice"!
|
||||
|
||||
### 2. Explicit in Tests
|
||||
- `OrientationTests.OrientationChanging_VirtualMethodCalledBeforeEvent`
|
||||
- `OrientationTests.OrientationChanged_VirtualMethodCalledBeforeEvent`
|
||||
|
||||
Tests would fail if order reversed.
|
||||
|
||||
### 3. Implicit in View Implementations
|
||||
|
||||
Many views override virtual methods with the ASSUMPTION they get first access:
|
||||
|
||||
**Example - TextView**:
|
||||
```csharp
|
||||
protected override bool OnMouseEvent (MouseEventArgs ev)
|
||||
{
|
||||
// TextView ASSUMES it processes mouse first
|
||||
// to update cursor position, selection, etc.
|
||||
// External code sees results AFTER TextView processes
|
||||
}
|
||||
```
|
||||
|
||||
**Example - ListView**:
|
||||
```csharp
|
||||
protected override bool OnKeyDown (Key key)
|
||||
{
|
||||
// ListView ASSUMES it processes keys first
|
||||
// to navigate items, select, etc.
|
||||
// External code sees results AFTER ListView processes
|
||||
}
|
||||
```
|
||||
|
||||
### 4. State Management Dependencies
|
||||
|
||||
Views often:
|
||||
1. Override `OnXxx` to UPDATE STATE first
|
||||
2. Then let event handlers see UPDATED STATE
|
||||
3. Event handlers may READ state assuming it's current
|
||||
|
||||
Reversing order means:
|
||||
1. Event handlers see OLD STATE
|
||||
2. Virtual method updates state AFTER
|
||||
3. Or: Event must prevent state update entirely
|
||||
|
||||
## Summary of Breaking Changes
|
||||
|
||||
### If Order Reversed Globally
|
||||
|
||||
**Code Changes Required**:
|
||||
1. Update 33+ virtual method implementations
|
||||
2. Update all view overrides (100+ locations)
|
||||
3. Update CWPWorkflowHelper
|
||||
4. Update CWPPropertyHelper
|
||||
5. Update documentation (events.md, cancellable-work-pattern.md)
|
||||
6. Update code comments explaining "best practice"
|
||||
7. Fix failing tests (OrientationTests and likely more)
|
||||
|
||||
**Affected Views** (partial list):
|
||||
- Slider (the issue trigger)
|
||||
- ListView
|
||||
- TextView, TextField, TextValidateField
|
||||
- TableView
|
||||
- TreeView
|
||||
- MenuBar, Menu
|
||||
- ScrollBar, ScrollSlider
|
||||
- TabView, TabRow
|
||||
- CheckBox, RadioGroup, Button
|
||||
- HexView
|
||||
- ColorBar
|
||||
- DateField, TimeField
|
||||
- And 20+ more...
|
||||
|
||||
**Risk Assessment**: **VERY HIGH**
|
||||
- Fundamental behavioral change
|
||||
- Breaks inheritance assumptions
|
||||
- Requires extensive testing
|
||||
- May break user code that depends on order
|
||||
|
||||
## Conclusion
|
||||
|
||||
The current CWP order (virtual method first, event second) is:
|
||||
1. **Explicitly documented** as "best practice" in code comments
|
||||
2. **Tested explicitly** by unit tests
|
||||
3. **Depended upon implicitly** by 100+ view implementations
|
||||
4. **Philosophically consistent** with inheritance-over-composition
|
||||
|
||||
Reversing the order would:
|
||||
1. **Solve issue #3714** (Slider mouse event prevention)
|
||||
2. **Enable external control** (composition-over-inheritance)
|
||||
3. **Break existing code** extensively
|
||||
4. **Require major refactoring** across codebase
|
||||
5. **Need comprehensive testing** and documentation updates
|
||||
|
||||
The choice represents a fundamental design philosophy trade-off:
|
||||
- **Current**: Tight coupling via inheritance (derived classes have priority)
|
||||
- **Proposed**: Loose coupling via composition (external code has priority)
|
||||
|
||||
Neither is "wrong" - it's a design decision with trade-offs either way.
|
||||
472
docs/analysis/cwp_recommendations.md
Normal file
472
docs/analysis/cwp_recommendations.md
Normal file
@@ -0,0 +1,472 @@
|
||||
# CWP Pattern Analysis - Executive Summary & Recommendations
|
||||
|
||||
## Quick Facts
|
||||
|
||||
- **Total CWP Implementations**: 33+ event pairs
|
||||
- **Virtual Method Overrides**: 100+ across codebase
|
||||
- **Current Order**: Virtual method → Event (inheritance priority)
|
||||
- **Proposed Order**: Event → Virtual method (composition priority)
|
||||
- **Breaking Change Magnitude**: VERY HIGH
|
||||
- **Estimated Effort**: 4-6 weeks for complete refactor
|
||||
- **Risk Level**: HIGH
|
||||
|
||||
## The Core Issue (#3714)
|
||||
|
||||
External code cannot prevent views like `Slider` from handling mouse events because:
|
||||
|
||||
```csharp
|
||||
// What users want but CANNOT do today:
|
||||
slider.MouseEvent += (s, e) =>
|
||||
{
|
||||
if (someCondition)
|
||||
e.Handled = true; // TOO LATE! Slider.OnMouseEvent already handled it
|
||||
};
|
||||
```
|
||||
|
||||
The virtual method (`OnMouseEvent`) runs first and can mark the event as handled, preventing the event from firing.
|
||||
|
||||
## Four Solution Options
|
||||
|
||||
### Option 1: Reverse Order Globally ⚠️ HIGH RISK
|
||||
|
||||
**Change**: Event first → Virtual method second (for all 33+ CWP patterns)
|
||||
|
||||
**Pros**:
|
||||
- Solves #3714 completely
|
||||
- Consistent pattern everywhere
|
||||
- Enables external control (composition over inheritance)
|
||||
- Single comprehensive solution
|
||||
|
||||
**Cons**:
|
||||
- MAJOR breaking change
|
||||
- 100+ view overrides need review/update
|
||||
- Changes fundamental framework philosophy
|
||||
- Breaks existing user code expectations
|
||||
- Requires extensive testing
|
||||
- Updates to helper classes, documentation, tests
|
||||
|
||||
**Effort**: 4-6 weeks
|
||||
**Risk**: VERY HIGH
|
||||
**Recommendation**: ❌ NOT RECOMMENDED unless major version change
|
||||
|
||||
### Option 2: Add "Before" Events 🎯 RECOMMENDED
|
||||
|
||||
**Change**: Add new pre-phase events (e.g., `BeforeMouseEvent`, `BeforeKeyDown`)
|
||||
|
||||
```csharp
|
||||
// New pattern for critical events
|
||||
protected bool RaiseMouseEvent(MouseEventArgs args)
|
||||
{
|
||||
// New: BeforeMouseEvent (external code gets first chance)
|
||||
BeforeMouseEvent?.Invoke(this, args);
|
||||
if (args.Handled)
|
||||
return true;
|
||||
|
||||
// Existing: OnMouseEvent (virtual method)
|
||||
if (OnMouseEvent(args) || args.Handled)
|
||||
return true;
|
||||
|
||||
// Existing: MouseEvent (external code gets second chance)
|
||||
MouseEvent?.Invoke(this, args);
|
||||
return args.Handled;
|
||||
}
|
||||
```
|
||||
|
||||
**Pros**:
|
||||
- Non-breaking (additive change only)
|
||||
- Solves #3714 for mouse events
|
||||
- Can apply selectively to problematic events
|
||||
- Gradual migration path
|
||||
- Clear intent (Before/During/After phases)
|
||||
|
||||
**Cons**:
|
||||
- More API surface
|
||||
- Two patterns coexist (inconsistency)
|
||||
- More complex for new developers
|
||||
- Partial solution only
|
||||
|
||||
**Implementation Plan**:
|
||||
1. **Phase 1** (1 week): Add `BeforeMouseEvent`, `BeforeMouseClick`, `BeforeMouseWheel`
|
||||
2. **Phase 2** (1 week): Add `BeforeKeyDown` if needed
|
||||
3. **Phase 3** (ongoing): Add others as needed, deprecate old pattern gradually
|
||||
|
||||
**Effort**: 2-3 weeks initial, ongoing refinement
|
||||
**Risk**: LOW
|
||||
**Recommendation**: ✅ **RECOMMENDED** - Best balance of solving issue vs. risk
|
||||
|
||||
### Option 3: Add `MouseInputEnabled` Property 🔧 QUICK FIX
|
||||
|
||||
**Change**: Add property to View to disable mouse handling
|
||||
|
||||
```csharp
|
||||
public class View
|
||||
{
|
||||
public bool MouseInputEnabled { get; set; } = true;
|
||||
|
||||
public bool? NewMouseEvent(MouseEventArgs mouseEvent)
|
||||
{
|
||||
if (!MouseInputEnabled)
|
||||
return false; // Don't process
|
||||
|
||||
// ... existing code
|
||||
}
|
||||
}
|
||||
|
||||
// Usage
|
||||
slider.MouseInputEnabled = false; // Disable slider mouse handling
|
||||
```
|
||||
|
||||
**Pros**:
|
||||
- Minimal change
|
||||
- Solves immediate #3714 issue
|
||||
- No breaking changes
|
||||
- Easy to implement
|
||||
- Easy to understand
|
||||
|
||||
**Cons**:
|
||||
- Band-aid solution (doesn't address root cause)
|
||||
- Mouse-specific (doesn't help keyboard, etc.)
|
||||
- All-or-nothing (can't selectively disable)
|
||||
- Adds more properties to View
|
||||
|
||||
**Effort**: 1 week
|
||||
**Risk**: VERY LOW
|
||||
**Recommendation**: ⚠️ Acceptable as short-term fix, not long-term solution
|
||||
|
||||
### Option 4: Reverse Order for Mouse Only 🎯 TARGETED FIX
|
||||
|
||||
**Change**: Event first → Virtual method second, but ONLY for mouse events
|
||||
|
||||
**Pros**:
|
||||
- Solves #3714 directly
|
||||
- Limited scope reduces risk
|
||||
- Mouse is the primary concern
|
||||
- Clearer than "Before" events
|
||||
|
||||
**Cons**:
|
||||
- Inconsistent pattern (mouse different from keyboard)
|
||||
- Still breaking for mouse event overrides
|
||||
- Confusing to have different orders
|
||||
- Doesn't help future similar issues
|
||||
|
||||
**Effort**: 2 weeks
|
||||
**Risk**: MEDIUM
|
||||
**Recommendation**: ⚠️ Better than Option 1, but Option 2 is cleaner
|
||||
|
||||
## Detailed Recommendation: Option 2 (Before Events)
|
||||
|
||||
### Implementation Specification
|
||||
|
||||
#### For Mouse Events (High Priority)
|
||||
|
||||
```csharp
|
||||
public partial class View // Mouse APIs
|
||||
{
|
||||
/// <summary>
|
||||
/// Event raised BEFORE OnMouseEvent is called, allowing external code
|
||||
/// to cancel mouse event processing before the view handles it.
|
||||
/// </summary>
|
||||
public event EventHandler<MouseEventArgs>? BeforeMouseEvent;
|
||||
|
||||
/// <summary>
|
||||
/// Event raised BEFORE OnMouseClick is called, allowing external code
|
||||
/// to cancel mouse click processing before the view handles it.
|
||||
/// </summary>
|
||||
public event EventHandler<MouseEventArgs>? BeforeMouseClick;
|
||||
|
||||
public bool RaiseMouseEvent (MouseEventArgs mouseEvent)
|
||||
{
|
||||
// Phase 1: Before event (external pre-processing)
|
||||
BeforeMouseEvent?.Invoke(this, mouseEvent);
|
||||
if (mouseEvent.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Phase 2: Virtual method (view processing)
|
||||
if (OnMouseEvent (mouseEvent) || mouseEvent.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Phase 3: After event (external post-processing)
|
||||
MouseEvent?.Invoke (this, mouseEvent);
|
||||
|
||||
return mouseEvent.Handled;
|
||||
}
|
||||
|
||||
protected bool RaiseMouseClickEvent (MouseEventArgs args)
|
||||
{
|
||||
if (!Enabled)
|
||||
{
|
||||
return args.Handled = false;
|
||||
}
|
||||
|
||||
// Phase 1: Before event
|
||||
BeforeMouseClick?.Invoke(this, args);
|
||||
if (args.Handled)
|
||||
{
|
||||
return args.Handled;
|
||||
}
|
||||
|
||||
// Phase 2: Virtual method
|
||||
if (OnMouseClick (args) || args.Handled)
|
||||
{
|
||||
return args.Handled;
|
||||
}
|
||||
|
||||
// Phase 3: After event
|
||||
MouseClick?.Invoke (this, args);
|
||||
|
||||
if (args.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Post-conditions
|
||||
args.Handled = InvokeCommandsBoundToMouse (args) == true;
|
||||
|
||||
return args.Handled;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
#### Usage Example (Solves #3714)
|
||||
|
||||
```csharp
|
||||
var slider = new Slider();
|
||||
|
||||
// NOW THIS WORKS - external code can prevent slider from handling mouse
|
||||
slider.BeforeMouseEvent += (sender, args) =>
|
||||
{
|
||||
if (someCondition)
|
||||
{
|
||||
args.Handled = true; // Prevents Slider.OnMouseEvent from being called
|
||||
}
|
||||
};
|
||||
|
||||
// Or use lambda with specific logic
|
||||
slider.BeforeMouseEvent += (sender, args) =>
|
||||
{
|
||||
if (args.Flags.HasFlag(MouseFlags.Button1Clicked) && IsModalDialogOpen())
|
||||
{
|
||||
args.Handled = true; // Block slider interaction when dialog is open
|
||||
}
|
||||
};
|
||||
```
|
||||
|
||||
#### For Keyboard Events (Medium Priority)
|
||||
|
||||
```csharp
|
||||
public partial class View // Keyboard APIs
|
||||
{
|
||||
/// <summary>
|
||||
/// Event raised BEFORE OnKeyDown is called, allowing external code
|
||||
/// to cancel key event processing before the view handles it.
|
||||
/// </summary>
|
||||
public event EventHandler<Key>? BeforeKeyDown;
|
||||
|
||||
public bool NewKeyDownEvent (Key k)
|
||||
{
|
||||
// Phase 1: Before event
|
||||
BeforeKeyDown?.Invoke(this, k);
|
||||
if (k.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Phase 2: Virtual method
|
||||
if (OnKeyDown (k) || k.Handled)
|
||||
{
|
||||
return true;
|
||||
}
|
||||
|
||||
// Phase 3: After event (existing KeyDown)
|
||||
KeyDown?.Invoke (this, k);
|
||||
|
||||
return k.Handled;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
#### For Other Events (Low Priority - As Needed)
|
||||
|
||||
Add `Before*` events for other patterns only if/when users request them.
|
||||
|
||||
### Migration Path
|
||||
|
||||
#### v2.x (Current)
|
||||
- Keep existing pattern
|
||||
- Add `Before*` events
|
||||
- Document both patterns
|
||||
- Mark as "preferred" for external control
|
||||
|
||||
#### v3.0 (Future)
|
||||
- Consider deprecating old pattern
|
||||
- Maybe reverse order globally
|
||||
- Or standardize on Before/After pattern
|
||||
|
||||
### Documentation Updates
|
||||
|
||||
Add to `docfx/docs/events.md`:
|
||||
|
||||
````markdown
|
||||
#### Three-Phase CWP Pattern
|
||||
|
||||
For critical events like mouse and keyboard input, a three-phase pattern is available:
|
||||
|
||||
```csharp
|
||||
public class MyView : View
|
||||
{
|
||||
public bool ProcessMouseEvent(MouseEventArgs args)
|
||||
{
|
||||
// Phase 1: BeforeMouseEvent - External pre-processing
|
||||
BeforeMouseEvent?.Invoke(this, args);
|
||||
if (args.Handled) return true;
|
||||
|
||||
// Phase 2: OnMouseEvent - View processing (virtual method)
|
||||
if (OnMouseEvent(args) || args.Handled) return true;
|
||||
|
||||
// Phase 3: MouseEvent - External post-processing
|
||||
MouseEvent?.Invoke(this, args);
|
||||
return args.Handled;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
**When to use each phase**:
|
||||
|
||||
- **BeforeXxx**: Use when you need to prevent the view from processing the event
|
||||
- Example: Disabling a slider when a modal dialog is open
|
||||
- Example: Implementing global keyboard shortcuts
|
||||
|
||||
- **OnXxx**: Override in derived classes to customize view behavior
|
||||
- Example: Custom mouse handling in a custom view
|
||||
- Example: Custom key handling in a specialized control
|
||||
|
||||
- **Xxx**: Use for external observation and additional processing
|
||||
- Example: Logging mouse activity
|
||||
- Example: Implementing additional behavior without inheritance
|
||||
````
|
||||
|
||||
### Testing Strategy
|
||||
|
||||
1. **Unit Tests**: Add tests for new Before* events
|
||||
2. **Integration Tests**: Test interaction between phases
|
||||
3. **Scenario Tests**: Test #3714 scenario specifically
|
||||
4. **Regression Tests**: Ensure existing code still works
|
||||
5. **Documentation Tests**: Verify examples work
|
||||
|
||||
### Benefits of This Approach
|
||||
|
||||
1. **Solves #3714**: Users can now prevent Slider from handling mouse
|
||||
2. **Non-Breaking**: All existing code continues to work
|
||||
3. **Clear Intent**: "Before" explicitly means "external pre-processing"
|
||||
4. **Selective Application**: Add to problematic events, not all 33
|
||||
5. **Future-Proof**: Creates migration path to v3.0
|
||||
6. **Minimal Risk**: Additive only, no changes to existing behavior
|
||||
7. **Gradual Adoption**: Users can adopt at their own pace
|
||||
|
||||
### Risks & Mitigations
|
||||
|
||||
**Risk**: Three phases more complex than two
|
||||
**Mitigation**: Good documentation, clear examples, gradual rollout
|
||||
|
||||
**Risk**: People still use wrong phase
|
||||
**Mitigation**: Intellisense XML docs explain when to use each
|
||||
|
||||
**Risk**: Two patterns coexist
|
||||
**Mitigation**: Document clearly, provide migration examples
|
||||
|
||||
## Alternative Considerations
|
||||
|
||||
### Could We Just Fix Slider?
|
||||
|
||||
No - this is a systemic issue. Any view that overrides `OnMouseEvent` has the same problem. Fixing just Slider doesn't help:
|
||||
- ListView
|
||||
- TextView
|
||||
- TableView
|
||||
- TreeView
|
||||
- ScrollBar
|
||||
- And 20+ others
|
||||
|
||||
### Could We Change Slider To Not Override OnMouseEvent?
|
||||
|
||||
Yes, but:
|
||||
- Still doesn't solve systemic issue
|
||||
- Other views have same problem
|
||||
- Not a general solution
|
||||
- Slider's implementation is reasonable
|
||||
|
||||
### Could We Add Multiple Overload Virtual Methods?
|
||||
|
||||
E.g., `OnMouseEventBefore` and `OnMouseEventAfter`?
|
||||
|
||||
No - virtual methods can't solve this because:
|
||||
- External code can't override virtual methods
|
||||
- Virtual methods are for inheritance, not composition
|
||||
- Issue is specifically about external code priority
|
||||
|
||||
## Implementation Checklist (Option 2)
|
||||
|
||||
- [ ] **Week 1: Mouse Events**
|
||||
- [ ] Add `BeforeMouseEvent` to View
|
||||
- [ ] Add `BeforeMouseClick` to View
|
||||
- [ ] Add `BeforeMouseWheel` to View
|
||||
- [ ] Update `RaiseMouseEvent` to invoke BeforeMouseEvent
|
||||
- [ ] Update `RaiseMouseClickEvent` to invoke BeforeMouseClick
|
||||
- [ ] Update `RaiseMouseWheelEvent` to invoke BeforeMouseWheel
|
||||
- [ ] Add unit tests for new events
|
||||
- [ ] Test Slider scenario specifically
|
||||
|
||||
- [ ] **Week 2: Documentation & Examples**
|
||||
- [ ] Update `events.md` with three-phase pattern
|
||||
- [ ] Update `cancellable-work-pattern.md` with new pattern
|
||||
- [ ] Add examples showing how to use BeforeMouseEvent
|
||||
- [ ] Add example solving #3714 specifically
|
||||
- [ ] Update API docs (XML comments)
|
||||
|
||||
- [ ] **Week 3: Keyboard Events (If Needed)**
|
||||
- [ ] Assess if keyboard has similar issues
|
||||
- [ ] Add `BeforeKeyDown` if needed
|
||||
- [ ] Add unit tests
|
||||
- [ ] Update documentation
|
||||
|
||||
- [ ] **Week 4: Other Events (As Needed)**
|
||||
- [ ] Assess other event patterns
|
||||
- [ ] Add Before* events as needed
|
||||
- [ ] Update documentation
|
||||
|
||||
- [ ] **Week 5-6: Testing & Refinement**
|
||||
- [ ] Integration testing
|
||||
- [ ] Scenario testing
|
||||
- [ ] User testing
|
||||
- [ ] Bug fixes
|
||||
- [ ] Documentation refinement
|
||||
|
||||
## Conclusion
|
||||
|
||||
**Recommended Solution**: **Option 2 - Add Before Events**
|
||||
|
||||
This solution:
|
||||
✅ Solves issue #3714
|
||||
✅ Non-breaking change
|
||||
✅ Clear and understandable
|
||||
✅ Minimal risk
|
||||
✅ Provides migration path
|
||||
✅ Can be applied selectively
|
||||
|
||||
Estimated effort: **2-3 weeks**
|
||||
Risk level: **LOW**
|
||||
|
||||
The key insight is that we don't need to change the existing pattern - we can ADD to it. This preserves all existing behavior while enabling the new use cases that #3714 requires.
|
||||
|
||||
## References
|
||||
|
||||
- Issue #3714: Mouse event interception problem
|
||||
- Issue #3417: Related mouse event handling issue
|
||||
- `docfx/docs/events.md`: Current CWP documentation
|
||||
- `docfx/docs/cancellable-work-pattern.md`: CWP philosophy
|
||||
- `Terminal.Gui/ViewBase/View.Mouse.cs`: Mouse event implementation
|
||||
- `Terminal.Gui/ViewBase/View.Keyboard.cs`: Keyboard event implementation
|
||||
- `Terminal.Gui/App/CWP/CWPWorkflowHelper.cs`: CWP helper class
|
||||
Reference in New Issue
Block a user