commands-behaviors-patterns

# Commands and Behaviors Patterns Agent models user interaction through `ICommand`, relay commands, and behavior-based event mapping so views stay declarative and view models stay testable. ## When to Use | Condition | Use | |---|---| | Work replaces click handlers or selection events with command bindings | Use this skill | | Work adds parameterized commands or async UI actions | Use this skill | | Work needs `CanExecute` state that reacts to view-model changes | Use this skill | | Work maps UI events to commands through behaviors or attached properties | Use this skill | ## When Not to Use | Condition | Route | |---|---| | Work defines overall MVVM architecture only | Use `mvvm-patterns-dotnet` | | Work focuses on binding syntax, update triggers, or converters | Use `databinding-patterns` | | Work edits background services with no UI interaction | Use the matching service skill | | Work follows a deliberate framework pattern that keeps view-only event handlers | Follow the existing pattern | ## Required Inputs | Input | Required | Notes | |---|---|---| | User actions | Yes | Identify triggers, parameters, and enabled state. | | Async behavior | Yes | Identify loading, cancellation, and duplicate-invocation rules. | | Target platforms | Yes | Identify WPF, MAUI, WinUI 3, or UWP behavior options. | | Validation and guards | No | Identify `CanExecute` conditions. | | Navigation or messaging hooks | No | Identify downstream coordination paths. | ## Pattern Matrix | Scenario | Preferred Pattern | Guardrail | Pass Target | |---|---|---|---| | Simple synchronous action | `RelayCommand` or focused `ICommand` | Avoid async work in a synchronous command | Action stays readable and testable | | Parameterized action | `RelayCommand<T>` or equivalent typed command | Validate null or type drift early | Command receives the intended parameter shape | | Slow or remote action | `AsyncRelayCommand` or explicit async command wrapper | Block duplicate invocation while work is active | One operation runs and UI state resets predictably | | Unsupported direct command surface | Behavior or attached property | Keep business logic in the view model | Event reaches the intended command without code-behind drift | | Shell-level gesture or routed input | Platform command binding where the framework already uses it | Keep scope narrow and consistent | Keyboard and menu flows stay aligned | ## Workflow | Step | Agent Action | Test | Pass | |---|---|---|---| | 1 | Agent lists actions, parameters, and enablement rules. | Review the interaction map. | Each action has one command owner and guard rule. | | 2 | Agent selects the command type that matches async and parameter needs. | Review one command per action. | Command type matches the workflow. | | 3 | Agent wires `CanExecute` dependencies to observable state changes. | Toggle one guard property or selection path. | Enabled state updates without stale UI. | | 4 | Agent maps events through behaviors or attached properties when direct command binding is absent. | Trigger one event-to-command path. | Event flow reaches the intended command. | | 5 | Agent binds parameters deliberately and validates null or type drift. | Invoke one parameterized path. | Parameter arrives with the expected type and value. | | 6 | Agent verifies async reentry, error recovery, and cancellation handling. | Run one slow path and one failure path. | UI blocks duplicates and resets predictably. | ## Rules | Topic | Rule | |---|---| | Async commands | Use async-capable command types for async work. | | Enablement | Raise `CanExecuteChanged` from every dependent state change path. | | Behaviors | Route business changes back through the view-model command. | | Parameters | Bind typed objects or stable identifiers instead of fragile strings. | | Reentry | Guard against duplicate taps or clicks during in-flight work. | ## Verification Checklist | Check | Test | Pass | |---|---|---| | Action mapping | Review touched controls and view models. | No business action stays trapped in code-behind. | | `CanExecute` reactivity | Change one guard property and one selection path. | Enabled state updates immediately. | | Async reentry | Trigger rapid repeated input on one async path. | One operation runs and UI state resets at completion. | | Event-to-command wiring | Inspect XAML and behavior wiring. | Event mapping stays declarative. | | Parameter shape | Trigger one parameterized path. | Command receives the intended parameter shape. | ## Outputs - Interaction map with commands, parameters, and guards - Command type selection for synchronous and asynchronous actions - Behavior or attached-property plan for unsupported direct command surfaces - Verification steps for enablement, parameters, and async reentry