在 PyQt 的网格布局中使用 QPainter 制作小部件可滚动

Question

I just started using PyQt and I struggle with the layout and making the content scrollable. I have a MainWindow where I want to place multiple widgets.

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()

        self.top = 0
        self.left = 0
        self.width = 500
        self.height = 500

        layout = QtWidgets.QGridLayout()
        layout.addWidget(WidgetOne(), 0, 0)
        layout.addWidget(WidgetTwo(), 1, 1)

        widget = QtWidgets.QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)

        self.initMainWindow()

    def initMainWindow(self):
        self.setGeometry(self.top, self.left, self.width, self.height)
        self.show()

And in WidgetOne I draw something with QPainter

class WidgetOne(QtWidgets.QWidget):
    def __init__(self):
        super(WidgetOne, self).__init__()

    def paintEvent(self, event):
        painter = QtGui.QPainter(self)

        painter.setRenderHint(QtGui.QPainter.Antialiasing)
        painter.setPen(QtCore.Qt.red)
        painter.setBrush(QtCore.Qt.green)
        # draw something
        painter.end()

And now I want to make WidgetOne where I drew something scrollable. The area where I draw is larger than the ẁindow on the screen, so I want to be able to scroll over everything I have drawn. I know it is done with QScrollArea but I only found examples where the scrolling area is the whole grid and not just one cell of the grid.

I already appreciate help. Thank you (Any advice and improvements are also welcome.)

EDIT: I think I am getting there. Now I have scrollbars around the drawn stuff, but I cant scroll. I would guess I need to set a size somewhere, but I do not know where. I added this to the __init__() of MainWindow

        self.scroll = QtWidgets.QScrollArea()
        self.scroll.setWidgetResizable(True)
        self.scroll.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.scroll.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.scrollWidget = WidgetOne()
        self.scroll.setWidget(self.scrollWidget)

        layout.addWidget(self.scroll, 0, 0)

Answer 1

As you point out the solution is to use QScrollArea but its viewport takes the minimum size of the widget, but in your case there is no minimum size so just set the minimumSizeHint, the minimumSize or fixedSize:

import sys

from PyQt5 import QtCore, QtGui, QtWidgets


class WidgetOne(QtWidgets.QWidget):
    def paintEvent(self, event):
        painter = QtGui.QPainter(self)

        painter.setRenderHint(QtGui.QPainter.Antialiasing)
        painter.setPen(QtCore.Qt.red)
        painter.setBrush(QtCore.Qt.green)

    def minimumSizeHint(self):
        return QtCore.QSize(1000, 1000)


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)

        widget = QtWidgets.QWidget()
        layout = QtWidgets.QGridLayout(widget)

        widget_one = WidgetOne()
        # or
        # widget_one.setFixedSize(1000, 1000)
        # or
        # widget_one.setMinimumSize(1000, 1000)
        scroll = QtWidgets.QScrollArea(widgetResizable=True)
        scroll.setWidget(widget_one)

        layout.addWidget(scroll, 0, 0)
        # layout.addWidget(WidgetTwo(), 1, 1)
        self.setCentralWidget(widget)
        self.resize(500, 500)


def main():
    app = QtWidgets.QApplication.instance()
    if app is None:
        app = QtWidgets.QApplication([])

    w = MainWindow()
    w.show()

    sys.exit(app.exec_())


if __name__ == "__main__":
    main()