Frozen widgets in QScrollArea

I’m trying to create a grid of square buttons that is scrollable if the window is too small to show all of them. I’d like there to be labels on the left-most column and top-most row showing the button indices.

Is there a way to create a QScrollArea with the widgets (labels) in the top-most row and left-most column “frozen”. Similar to how you can freeze rows and columns in an Excel Sheet where they follow the view around as you scroll.

See a mockup here:

Either Qt and PyQt are welcome.

Answer

I solved my problem with multiple QScrollAreas using the method outlined in this answer. The idea is to have the frozen areas be QScrollArea with disabled scrolling, while the unfrozen QScrollArea scrollbar signals are connected to the frozen QScrollArea scrollbar slots.

Here is the code of my mockup with the top-most row and left-most column frozen. The especially relevant parts are the FrozenScrollArea class and the connections inside the Window class.

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import (
    QApplication,
    QPushButton,
    QWidget,
    QScrollArea,
    QGridLayout,
    QLabel,
    QFrame,
    QSpacerItem,
    QSizePolicy,
    )


ROWS = 10
COLS = 20
SIZE = 35


style = """
Button {
    padding: 0;
    margin: 0;
    border: 1px solid black;
}
Button::checked {
    background-color: lightgreen;
}
"""


class Button(QPushButton):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setFixedSize(SIZE, SIZE)
        self.setCheckable(True)
        self.setStyleSheet(style)


class Label(QLabel):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setAlignment(Qt.AlignCenter)
        self.setFixedSize(SIZE, SIZE)


class Labels(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        layout = QGridLayout()
        layout.setHorizontalSpacing(0)
        layout.setVerticalSpacing(0)
        layout.setContentsMargins(0, 0, 0, 0)
        self.setLayout(layout)


class FrozenScrollArea(QScrollArea):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setWidgetResizable(True)
        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.verticalScrollBar().setEnabled(False)
        self.horizontalScrollBar().setEnabled(False)


class FrozenRow(FrozenScrollArea):
    def __init__(self, parent):
        super().__init__()

        labels = Labels(parent)
        for c in range(COLS):
            label = Label(self, text = str(c))
            labels.layout().addWidget(label, 0, c, 1, 1, Qt.AlignCenter)

        labels.layout().addItem(QSpacerItem(0, 0, QSizePolicy.Expanding, QSizePolicy.Minimum), 0, COLS, 1, 1)

        self.setFrameShape(QFrame.NoFrame)
        self.setFixedHeight(SIZE)
        self.setWidget(labels)


class FrozenColumn(FrozenScrollArea):
    def __init__(self, parent):
        super().__init__()

        labels = Labels(parent)
        for r in range(ROWS):
            label = Label(self, text = str(r))
            labels.layout().addWidget(label, r, 0, 1, 1, Qt.AlignCenter)

        labels.layout().addItem(QSpacerItem(0, 0, QSizePolicy.Minimum, QSizePolicy.Expanding), ROWS, 0, 1, 1)

        self.setFrameShape(QFrame.NoFrame)
        self.setFixedWidth(SIZE)
        self.setWidget(labels)


class ButtonGroup(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QGridLayout()
        for r in range(ROWS):
            for c in range(COLS):
                button = Button(self)
                layout.addWidget(button, r, c, 1, 1)

        layout.setHorizontalSpacing(0)
        layout.setVerticalSpacing(0)
        layout.setContentsMargins(0, 0, 0, 0)

        self.setLayout(layout)


class Buttons(QScrollArea):
    def __init__(self, parent):
        super().__init__()
        self.setFrameShape(QFrame.NoFrame)
        self.setWidget(ButtonGroup(parent))


class Window(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        # layout
        layout = QGridLayout()
        self.setLayout(layout)
        layout.setHorizontalSpacing(0)
        layout.setVerticalSpacing(0)
        layout.setContentsMargins(0, 0, 0, 0)

        # frozen row (top)
        self.frozenRow = FrozenRow(self)
        layout.addWidget(self.frozenRow, 0, 1, 1, 1)

        # frozen column (left)
        self.frozenColumn = FrozenColumn(self)
        layout.addWidget(self.frozenColumn, 1, 0, 1, 1)

        # button grid
        self.buttons = Buttons(self)
        layout.addWidget(self.buttons, 1, 1, 1, 1)

        # scrollbar connections
        self.buttons.horizontalScrollBar().valueChanged.connect(self.frozenRow.horizontalScrollBar().setValue)  # horizontal scroll affects frozen row only
        self.buttons.verticalScrollBar().valueChanged.connect(self.frozenColumn.verticalScrollBar().setValue)  # vertical scroll affects frozemn column only

        self.show()


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = Window()
    sys.exit(app.exec())