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')

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