PySide6 MVC Architecture Instructions
Guidelines for building Python desktop applications using PySide6 with strict MVC architecture where all UI is defined by .ui files.
Architecture Overview
┌─────────────────────────────────────────┐
│ View Layer (.ui files) │
│ Load from Qt Designer, capture input │
└──────────────────┬──────────────────────┘
│ Signals
┌──────────────────▼──────────────────────┐
│ Controller Layer │
│ Coordinate models & services │
└──────────────────┬──────────────────────┘
│
┌──────────────────▼──────────────────────┐
│ Model Layer │
│ Data structures, validation │
└──────────────────┬──────────────────────┘
│
┌──────────────────▼──────────────────────┐
│ Services Layer │
│ Database, files, network, broker │
└─────────────────────────────────────────┘Project Structure
my_app/
├── app.py # Bootstrap & DI container
├── __main__.py # Entry point
├── controllers/
│ ├── base.py # BaseController
│ └── *_controller.py # Domain controllers
├── models/
│ ├── base.py # BaseModel with signals
│ └── *.py # Domain models
├── views/
│ ├── base.py # BaseView
│ └── *.py # View classes
├── services/
│ └── *.py # External interactions
├── resources/
│ └── ui/ # .ui files (Qt Designer)
└── utils/
└── signals.py # Central signal registryCore Principles
| Component | Responsibility | Does NOT |
|---|---|---|
| Model | Data, validation, serialization | Touch UI, call services |
| View | Load.ui files, capture input | Contain business logic |
| Controller | Coordinate models & services | Manipulate UI directly |
Base Model Pattern
from PySide6.QtCore import QObject, Signal
from datetime import datetime
from typing import Any
class BaseModel(QObject):
property_changed = Signal(str, object) # name, value
changed = Signal()
def __init__(self, parent=None):
super().__init__(parent)
self._updated_at = datetime.now()
def _set_property(self, name: str, old: Any, new: Any) -> bool:
if old != new:
self._updated_at = datetime.now()
self.property_changed.emit(name, new)
self.changed.emit()
return True
return False
def to_dict(self) -> dict:
raise NotImplementedError
@classmethod
def from_dict(cls, data: dict):
raise NotImplementedErrorBase View Pattern
from pathlib import Path
from PySide6.QtWidgets import QWidget, QVBoxLayout
from PySide6.QtCore import QFile, Signal
from PySide6.QtUiTools import QUiLoader
class BaseView(QWidget):
error_occurred = Signal(str, str) # title, message
def __init__(self, parent=None):
super().__init__(parent)
self._controller = None
self._init_ui()
self._connect_signals()
def _load_ui(self, ui_filename: str) -> QWidget:
ui_path = Path(__file__).parent.parent / "resources" / "ui" / ui_filename
loader = QUiLoader()
ui_file = QFile(str(ui_path))
if ui_file.open(QFile.ReadOnly):
ui = loader.load(ui_file, self)
ui_file.close()
layout = QVBoxLayout(self)
layout.setContentsMargins(0, 0, 0, 0)
layout.addWidget(ui)
return ui
raise FileNotFoundError(f"Cannot open: {ui_path}")
def _init_ui(self):
pass # Override: load .ui file
def _connect_signals(self):
pass # Override: connect handlers
def set_controller(self, controller):
self._controller = controller
def refresh(self):
pass # Override: update from modelBase Controller Pattern
from PySide6.QtCore import QObject
class BaseController(QObject):
def __init__(self, signals, parent=None):
super().__init__(parent)
self._signals = signals
self._views = []
def register_view(self, view):
if view not in self._views:
self._views.append(view)
view.set_controller(self)
def notify_views(self):
for view in self._views:
view.refresh()
def initialize(self):
pass # Override: setup logic
def cleanup(self):
self._views.clear()Central Signal Registry
from PySide6.QtCore import QObject, Signal
class SignalRegistry(QObject):
# Domain signals
job_changed = Signal(str) # job_id
job_created = Signal(str) # job_id
settings_changed = Signal(str, object) # key, value
# Connection signals
broker_connected = Signal(bool) # connected
# UI signals
error_occurred = Signal(str, str) # title, message
app_closing = Signal()
# Singleton
_registry = None
def get_signal_registry():
global _registry
if _registry is None:
_registry = SignalRegistry()
return _registryApplication Bootstrap (DI Container)
import sys
from PySide6.QtWidgets import QApplication
from my_app.utils.signals import get_signal_registry
class MyApplication:
_instance = None
def __new__(cls):
if cls._instance is None:
cls._instance = super().__new__(cls)
return cls._instance
def __init__(self):
self._qt_app = None
self._services = {}
self._controllers = {}
self._signals = get_signal_registry()
def _register_services(self):
self._services["db"] = DatabaseService()
def _register_controllers(self):
self._controllers["job"] = JobController(
signals=self._signals,
db=self._services["db"],
)
for c in self._controllers.values():
c.initialize()
def run(self) -> int:
self._qt_app = QApplication(sys.argv)
self._register_services()
self._register_controllers()
window = MainWindow(self._signals, self._controllers)
window.show()
return self._qt_app.exec()Widget Naming Conventions (.ui files)
| Widget Type | Pattern | Example |
|---|---|---|
| Label | *_label | job_number_label |
| Button | *_btn | save_btn |
| Line Edit | *_input | customer_input |
| List | *_list | jobs_list |
| Table | *_table | pieces_table |
| Combo | *_combo | status_combo |
Signal Flow
User Action (View)
↓
View emits signal
↓
Controller handles action
↓
Service performs operation
↓
SignalRegistry.emit()
↓
Views call refresh()Best Practices
1. Never Create UI Programmatically
❌ Wrong:
layout = QVBoxLayout()
btn = QPushButton("Click")
layout.addWidget(btn)✅ Correct:
self._ui = self._load_ui("my_widget.ui")
self._btn = self._ui.findChild(QPushButton, "action_btn")2. Controllers Never Touch UI
❌ Wrong:
def activate_job(self):
self._view.label.setText(job.name) # NO!✅ Correct:
def activate_job(self):
self._signals.job_changed.emit(job_id) # Views subscribe3. Views Subscribe to Signals
def _connect_signals(self):
self._signals.job_changed.connect(self._on_job_changed)
def _on_job_changed(self, job_id):
self.refresh()4. Provide Fallback UI
def _init_ui(self):
try:
self._ui = self._load_ui("widget.ui")
except FileNotFoundError:
self._create_fallback_ui()5. Use Services for External Operations
Controllers delegate to services:
- Database queries → Repository services
- File operations → File service
- Network calls → API service
- IPC → Broker client
Common Imports
# Qt
from PySide6.QtWidgets import QWidget, QMainWindow
from PySide6.QtCore import Signal, Slot, QFile
from PySide6.QtUiTools import QUiLoader
# Project
from my_app.utils.signals import get_signal_registry
from my_app.controllers.base import BaseController
from my_app.views.base import BaseView
from my_app.models.base import BaseModel