Instruction file imported from Nargodian/CK3CoatOfArmsEditor (.github/instructions/archive/component-responsibility.instructions.md). Copyright stays with the author.

Component Responsibility Principle

Core Rule

Components query and set their own display properties. Don't pass display state through callbacks.

Selection Callbacks

Use selection callbacks ONLY for:

• Cross-component coordination (property sidebar updates when layer selected)
• System-level events (reordering, deletion affecting multiple components)

Do NOT use selection callbacks for:

• Component's own display properties
• Properties that component can query directly from CoA

Implementation Pattern

❌ WRONG - Callback sets display state

def _on_selection_changed():
    colors = coa.get_layer_colors(uuid)
    property_panel.set_emblem_color_count(colors)  # External setting

✅ CORRECT - Component queries its own state

def _load_layer_properties():
    colors = self.main_window.coa.get_layer_colors(uuid)
    self.set_emblem_color_count(colors)  # Self query and set

Callback Triggers

update_selection_visuals() should trigger on_selection_changed callback. Don't require manual callback invocation after selection changes.

Summary

If a property is entirely within component's view (color count, visibility, enabled state), component queries and sets it. Callbacks are for "something changed that you need to know about", not "here's your new state".