How to update QScrollArea size when contents change size? - qt

Question

My QScrollArea does not update its size dinamically when I add a new QPushButton inside it.
I want to add/remove some QPushButton inside a QScrollArea dinamically, but my QScrollArea does not update
its size.
I want my QScrollArea has always a minimum possible size.
With this code:
import sys
from PyQt5.QtWidgets import (QApplication, QWidget, QMainWindow,
QPushButton, QScrollArea, QVBoxLayout)
class MyWindow(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
scroll = QScrollArea(self)
scroll.setWidgetResizable(True)
# Contents
w = QWidget()
lay = QVBoxLayout(w)
lay.addWidget(QPushButton('Button'))
scroll.setWidget(w)
# Controls
button_add = QPushButton('Add')
button_add.clicked.connect(lambda: lay.addWidget(QPushButton('Button')))
button_del = QPushButton('Del')
button_del.clicked.connect(lambda: lay.takeAt(0).widget().deleteLater() if lay.count()>0 else None)
# Main Layout
vlay = QVBoxLayout()
vlay.addWidget(scroll)
vlay.addStretch()
vlay.addWidget(button_add)
vlay.addWidget(button_del)
w = QWidget(self)
w.setLayout(vlay)
self.setCentralWidget(w)
self.resize(200, 300)
if __name__ == '__main__':
app = QApplication([])
mainWin = MyWindow()
mainWin.show()
sys.exit(app.exec_())
I got this view (left) when started and (right) when I add some QPushButtons:
So I have two questions:
How I start my application with QScrollArea with a minimum size?
How QScrollAre can update its size dinamically?
My desirable view is:
And of course, when I add a lot of QPushButtons, a Scrollbar appears.

Answer 1

You can set maximum height for scrollarea equals to widget contents (layout size + margins). This should be done after layout completes it's calculations (for example asyncronously with zero-timer).
import sys
from PyQt5.QtCore import QTimer
from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow, QPushButton, QScrollArea, QVBoxLayout
class MyWindow(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
scroll = QScrollArea(self)
scroll.setWidgetResizable(True)
# Contents
w = QWidget()
lay = QVBoxLayout(w)
#lay.addWidget(QPushButton('Button'))
scroll.setWidget(w)
def updateSize():
left, top, right, bottom = lay.getContentsMargins()
hint = lay.sizeHint()
scroll.setMaximumHeight(hint.height() + top + bottom + 1)
def addButton():
lay.addWidget(QPushButton('Button'))
QTimer.singleShot(0, updateSize)
def removeButton():
if lay.count() > 0:
lay.takeAt(0).widget().deleteLater()
QTimer.singleShot(0, updateSize)
addButton()
# Controls
button_add = QPushButton('Add')
button_add.clicked.connect(addButton)
button_del = QPushButton('Del')
button_del.clicked.connect(removeButton)
# Main Layout
vlay = QVBoxLayout()
vlay.addWidget(scroll)
vlay.addStretch(1)
vlay.addWidget(button_add)
vlay.addWidget(button_del)
vlay.setStretch(0,1000)
w = QWidget(self)
w.setLayout(vlay)
self.setCentralWidget(w)
self.resize(200, 300)
if __name__ == '__main__':
app = QApplication([])
mainWin = MyWindow()
mainWin.show()
app.exec()