Avoid unnecessary repaints

xueqli

Hello!
When I update label text in the example below all of the items in the list are repainted. Without QTabWidget (with plain QWidget, for example) the paintEvent is not triggered when text size is unchanged, but inside of a tab repaint happens after each label update.
Is there a way to avoid these repaints with QTabWidget?
Example:

from PyQt6.QtCore import QModelIndex
from PyQt6.QtCore import QTimer
from PyQt6.QtGui import QPainter
from PyQt6.QtWidgets import QApplication
from PyQt6.QtWidgets import QHBoxLayout
from PyQt6.QtWidgets import QLabel
from PyQt6.QtWidgets import QListWidget
from PyQt6.QtWidgets import QMainWindow
from PyQt6.QtWidgets import QStyledItemDelegate
from PyQt6.QtWidgets import QStyleOptionViewItem
from PyQt6.QtWidgets import QTabWidget
from PyQt6.QtWidgets import QWidget


class Delegate(QStyledItemDelegate):
    def __init__(self) -> None:
        QStyledItemDelegate.__init__(self)
        self.counter = 0

    def paint(self, painter: QPainter, option: QStyleOptionViewItem, index: QModelIndex) -> None:
        print("paint!", self.counter)
        self.counter += 1
        QStyledItemDelegate.paint(self, painter, option, index)


class Widget(QWidget):
    def __init__(self) -> None:
        QWidget.__init__(self)

        self.label = QLabel()
        self.label.setText("00")

        self.list_widget = QListWidget()
        self.list_widget.setItemDelegate(Delegate())
        self.list_widget.addItems(map(str, range(100)))
        self.list_widget.setViewMode(QListWidget.ViewMode.IconMode)

        hbox = QHBoxLayout()
        hbox.addWidget(self.label)
        hbox.addWidget(self.list_widget)
        self.setLayout(hbox)

        self.counter = 0

        self.timer = QTimer()
        self.timer.timeout.connect(self.on_timeout)
        self.timer.start(1000)

    def on_timeout(self) -> None:
        self.counter += 1
        self.label.setText(f"{self.counter:02}")


class Window(QMainWindow):
    def __init__(self) -> None:
        QMainWindow.__init__(self)
        self.widget = Widget()
        self.tabs = QTabWidget()
        self.tabs.addTab(self.widget, "asdf")
        self.setCentralWidget(self.tabs)


def main() -> int:
    app = QApplication(["asdf"])
    w = Window()
    w.show()
    return app.exec()


if __name__ == "__main__":
    raise SystemExit(main())

JoeCFD

You may try:

get visial rect of the item
QRect QTableWidget::visualItemRect(const QTableWidgetItem *item) const
update it only
void QWidget::update(const QRect &rect)

check here out
https://www.qtcentre.org/threads/1032-repaint-a-cell-or-row-in-QTableWidget