Get QScrollArea absolute size

Question

I have a custom widget that is a child of a QScrollArea. I need to get the absolute size of the QScrollArea, regardless of scrollbars being displayed or not.

class MyWidget : public QWidget { /*...*/ };

void
MyWidget::Foo()
{
    auto scrollAreaHeight = parentWidget()->height();
    auto scrollAreaWidth = parentWidget()->width();

    /* height and width change depending on scrollbars 
       being displayed or not */
}

Is there a way to do this?

Alternatively, if this is impossible trough the QWidget interface returned by the parentWidget() function, is there a way to get a QScrollArea's absolute size from the QScrollArea itself?

Answer 1

I don't understand completely why OP cannot get the absolute size of QScrollArea.

However, I assume there might be something missing in OP's understanding. I prepared the following small sample:

A QWidget with a QVBoxLayout with a QScrollArea with a QPushButton:

#!/usr/bin/python3

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QScrollArea, QPushButton

app = QApplication(sys.argv)
qWinMain = QWidget()
qVBox = QVBoxLayout()
qScrollArea = QScrollArea()
qBtn = QPushButton("Consume somehow some space\nConsume somehow some space\nConsume somehow some space\n")
qScrollArea.setWidget(qBtn)
qVBox.addWidget(qScrollArea)
qWinMain.setLayout(qVBox)
qWinMain.show()

def onBtnClicked():
  print("Sizes:")
  print("qWinMain:               ", qWinMain.size())
  print("qWinMain.childrenRect():", qWinMain.childrenRect().size())
  print("qScrollArea:            ", qScrollArea.size())
  print("qScrollArea.viewport(): ", qScrollArea.viewport().size())
  print("qBtn:                   ", qBtn.size())

qBtn.clicked.connect(onBtnClicked)
sys.exit(app.exec_())

When the QPushButton is clicked, some sizes of the widgets are printed. It did this twice – once when scrollbars are invisible, and again after I changed size of main window so that scrollbars became visible.

Output:

Sizes:
qWinMain:                PyQt5.QtCore.QSize(225, 100)
qWinMain.childrenRect(): PyQt5.QtCore.QSize(203, 78)
qScrollArea:             PyQt5.QtCore.QSize(203, 78)
qScrollArea.viewport():  PyQt5.QtCore.QSize(201, 76)
qBtn:                    PyQt5.QtCore.QSize(201, 65)
Sizes:
qWinMain:                PyQt5.QtCore.QSize(120, 92)
qWinMain.childrenRect(): PyQt5.QtCore.QSize(98, 70)
qScrollArea:             PyQt5.QtCore.QSize(98, 70)
qScrollArea.viewport():  PyQt5.QtCore.QSize(82, 54)
qBtn:                    PyQt5.QtCore.QSize(201, 65)

So, this is how to read this:

• qWinMain.size() returned client area size of qWinMain (not considering window decorations).
• qWinMain.childrenRect().size() returned bounding box size of children of qWinMain – It's exactly 22 pixels smaller in width and height what makes sense as 11 pixels is the default margin of QWidget.
• qScrollArea.size() returned the exact same size like qWinMain.childrenRect().size() in both cases which is reasonable as it's the only child.
• qScrollArea.viewport().size() returns the viewport size of QScrollArea – that size is dependend on whether scrollbars are visible or not. Without scrollbars, the difference to qScrollArea is only 2 pixels in width and height but with scrollbars it's respectively greater.
• qBtn.size() returns size of push button which is independent of its visual/clipped regions and, hence, in both cases equal.

So, whatever OP meant with "absolute size of QScrollArea" – one of these should be OP is looking for.