在 Qt5 中在运行时替换小部件

Question

I have this Qt5 GUI that I'm making in python3(.8). It has a QButtonGroup on the left side. Pressing one of these buttons should present the associated device QWidget class that is made (not shown here) on the right side. So only 2 widgets are present in the main layout.

This code runs. I know the functionality doens't really make sense in device_clicked but it's just for having a small working code snippet to demonstrate.

import logging
import sys

from PyQt5.QtWidgets import (QApplication, QButtonGroup, QHBoxLayout, QTabBar, QTabWidget,
                             QMainWindow, QPushButton, QVBoxLayout, QWidget, QLabel)

logging.basicConfig(
    format="%(asctime)s,%(msecs)d - %(name)s - %(levelname)s: %(message)s",
    datefmt="%H:%M:%S",
    level=logging.INFO,
)

DEVICES = [("DEV1", QLabel), ("2222", QLabel), ("HUPP", QLabel), ("FOOO", QLabel), ("BOOO", QLabel)]


class MainApp(QMainWindow):
    """Documentation for MainApp(QMainWindow)

    """
    def __init__(self):
        super().__init__()

        self.logger = logging.getLogger("MAIN")
        self.logger.info("Starting main program")

        self.title = "Title"
        self.left = 300
        self.top = 200
        self.width = 1100
        self.height = 600

        self.init_ui()

    def init_ui(self) -> None:
        """
        Initializs the UI
        """
        self.logger.info("Starting UI")

        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)

        self.main_widget = QWidget()
        self.setCentralWidget(self.main_widget)

        layout = QHBoxLayout()
        self.main_widget.setLayout(layout)

        dev_layout = QVBoxLayout()
        self.devices = QButtonGroup()
        for i, (t, w) in enumerate(DEVICES):
            btn = QPushButton(t)
            self.devices.addButton(btn, i)
            dev_layout.addWidget(btn)

        self.devices.buttonClicked[int].connect(self.device_clicked)

        layout.addLayout(dev_layout, 10)
        layout.addWidget(QLabel("test"), 90)
        self.prev_device_id = 0
        self.devices.button(0).setDown(True)

    def device_clicked(self, btn_id: int) -> None:
        self.logger.info(f"BTN {btn_id} clicked")
        self.devices.button(self.prev_device_id).setDown(False)
        self.devices.button(btn_id).setDown(True)

        # replace gives my an AttributeError: 'QHBoxLayout' object has no attribute 'replace'
        # self.main_widget.layout().replace(DEVICES[self.prev_device_id][1], DEVICES[btn_id][1])

        self.main_widget.layout().takeAt(1)
        self.main_widget.layout().addWidget(DEVICES[btn_id][1](DEVICES[btn_id][0]), 90)
        self.main_widget.layout().update()

        self.prev_device_id = btn_id

if __name__ == "__main__":
    app = QApplication(sys.argv)
    main = MainApp()
    main.show()
    app.exec_()

The problem I have now, is that the old widget isn't deleted and the new widget is placed over it, displaying them both at the same time.

Is it because the MainApp is a QMainWindow and has a self.main_widget = QWidget() centralWidget? Is it recommended to work with setCentralWidget() ?

Answer 1

takeAt() only removes the layout item from the layout, it doesn't delete its widget. Note that I specified layout item , because layouts use QLayoutItems , which are abstract items that the layout uses to manage its contents: a layout item could contain a layout itself, or a widget.

In any case, after removing the widget (either by removing the layout item or the widget itself by using removeWidget() ), you also have to call deleteLater() .
This is necessary because, even after removing a widget from a layout, the widget will still have a parent set (the widget on which the layout was set).

    layoutItem = self.main_widget.layout().itemAt(1)
    if layoutItem.widget():
        layoutItem.widget().deleteLater()

or, if you already have the reference to the widget:

    self.someWidget.deleteLater()