qgis-core

QGIS Core Development

Standardizes interaction with the QGIS API, ensuring a responsive and well-structured plugin.

When to use this skill

• When implementing new tools that interact with the map canvas.
• When handling vector or raster layers.
• When performing heavy operations that require secondary threads.

Degree of Freedom

• Strict: The use of QgsTask for long processes and Core/GUI decoupling are mandatory.

Workflow

1. Architecture: Separate logic into core/ (processing) and gui/ (visualization).
2. Validation: Always verify isValid() on layers before operating.
3. Asynchrony: Wrap processes > 0.5s in a QgsTask.
4. CRS Management: Explicitly handle coordinate transformations.

Instructions and Rules

Golden Rules

• QgsTask: Do not block the UI. Use signals and slots for communication.
• Network/Threads: Avoid threading.Thread (use QgsTask) and synchronous network calls (rules UNSAFE_THREAD and BLOCKING_NETWORK_CALL).
• Boundaries: Use WKT to communicate core logic with the graphical interface.
• Modernization: Avoid legacy QVariant; the analyzer will detect OBSOLETE_VARIANT.
• Injection: Avoid global use of iface; prefer passing objects in constructors.

Plugin Structure

• core/: Business logic agnostic to the UI.
• gui/: Widgets and dialogs dependent on PyQGIS.
• exporters/: Data output modules.

Quality Checklist

• Is UI blocking avoided through QgsTask?
• Is layer integrity validated in every operation?
• Are CRS transformations explicitly defined?
• Is the Core/GUI separation of responsibilities followed?