Signal QscrollArea

Question

I would like to know is it possible to have a signal or something to know when the scroll is available and when it is no longer available each time the window is resized?

import sys
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *

class Widget(QWidget):
    def __init__(self, parent= None):
        super(Widget, self).__init__()

        widget = QWidget()

        layout = QVBoxLayout(self)

        for _ in range(10):
            btn = QPushButton()
            layout.addWidget(btn)

        widget.setLayout(layout)

        scroll = QScrollArea()
        scroll.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
        scroll.setWidget(widget)
        vLayout = QVBoxLayout(self)
        vLayout.addWidget(scroll)
        self.setLayout(vLayout)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    dialog = Widget()
    dialog.show()
    app.exec_()

Answer 1

Since a QScrollBar is usually visible only when its range maximum is greater than 0, you can just check that value.

class Widget(QWidget):
    def __init__(self, parent= None):
        # ....
        # note that the scroll area is now an instance member
        self.scroll = QScrollArea()
        self.scroll.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
        self.scroll.setWidget(widget)
        self.scroll.verticalScrollBar().rangeChanged.connect(self.checkScrollBarRange)
        vLayout = QVBoxLayout(self)
        vLayout.addWidget(self.scroll)
        self.setLayout(vLayout)

        # the next is important when resizing the widget containing the scroll area
        self.scroll.installEventFilter(self)

    def eventFilter(self, source, event):
        if source == self.scroll and event.type() == QEvent.Resize:
            self.checkScrollBarRange()
        return super().eventFilter(source, event)

    def checkScrollBarRange(self):
        if (self.scroll.verticalScrollBarPolicy() != Qt.ScrollBarAlwaysOff and
            self.scroll.verticalScrollBar().maximum()):
                print('vertical scroll bar IS visible')
        else:
            print('vertical scroll bar NOT visible')