I have a QScrollArea with a number of QTreeWidgets in it arranged into QVBoxLayout. Each tree widget has a single top-level item (but hierarchy of child items is arbitrary). Vertical scrollbars of individual tree widgets are disabled via setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff). I want vertical size of tree widgets to be dynamically changed when their items are expanded or collapsed, so I have set setSizeAdjustPolicy(QAbstractScrollArea::AdjustToContents) for each of the QTreeWidgets. Vertical size policies are set to minimum, and there is a vertical spacer put below all tree widgets. Layout spacing is set to 0. Now, it works like expected, except one thing: when a tree widget is entirely collapsed, it still takes too much vertical space, as shown in the picture. I just cannot figure out how to get rid of this extra space, so that the tree widgets were next to each other when collapsed.
.
The contents of the ui-form generated in the Qt Designer:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>241</width>
<height>526</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralwidget">
<layout class="QVBoxLayout" name="verticalLayout">
<property name="spacing">
<number>0</number>
</property>
<property name="sizeConstraint">
<enum>QLayout::SetMinimumSize</enum>
</property>
<property name="leftMargin">
<number>0</number>
</property>
<property name="topMargin">
<number>0</number>
</property>
<property name="rightMargin">
<number>0</number>
</property>
<property name="bottomMargin">
<number>0</number>
</property>
<item>
<widget class="QScrollArea" name="scrollArea">
<property name="sizePolicy">
<sizepolicy hsizetype="Minimum" vsizetype="Minimum">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="styleSheet">
<string notr="true">background-color: rgb(255, 255, 255);</string>
</property>
<property name="frameShape">
<enum>QFrame::NoFrame</enum>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="widgetResizable">
<bool>true</bool>
</property>
<widget class="QWidget" name="scrollAreaWidgetContents">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>241</width>
<height>480</height>
</rect>
</property>
<layout class="QVBoxLayout" name="verticalLayout_2">
<property name="spacing">
<number>10</number>
</property>
<property name="leftMargin">
<number>0</number>
</property>
<property name="topMargin">
<number>0</number>
</property>
<property name="rightMargin">
<number>0</number>
</property>
<property name="bottomMargin">
<number>0</number>
</property>
<item>
<widget class="QTreeWidget" name="treeWidget">
<property name="sizePolicy">
<sizepolicy hsizetype="Expanding" vsizetype="Minimum">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="frameShape">
<enum>QFrame::NoFrame</enum>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="verticalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="horizontalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="sizeAdjustPolicy">
<enum>QAbstractScrollArea::AdjustToContents</enum>
</property>
<property name="alternatingRowColors">
<bool>false</bool>
</property>
<property name="uniformRowHeights">
<bool>false</bool>
</property>
<property name="animated">
<bool>false</bool>
</property>
<property name="headerHidden">
<bool>true</bool>
</property>
<attribute name="headerVisible">
<bool>false</bool>
</attribute>
<column>
<property name="text">
<string>New Column</string>
</property>
</column>
<item>
<property name="text">
<string>TreeWidget1</string>
</property>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
</item>
</item>
</widget>
</item>
<item>
<widget class="QTreeWidget" name="treeWidget_2">
<property name="sizePolicy">
<sizepolicy hsizetype="Expanding" vsizetype="Minimum">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="frameShape">
<enum>QFrame::NoFrame</enum>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="verticalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="horizontalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="sizeAdjustPolicy">
<enum>QAbstractScrollArea::AdjustToContents</enum>
</property>
<property name="autoScroll">
<bool>true</bool>
</property>
<attribute name="headerVisible">
<bool>false</bool>
</attribute>
<column>
<property name="text">
<string>1</string>
</property>
</column>
<item>
<property name="text">
<string>TreeWidget2</string>
</property>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
</item>
</widget>
</item>
<item>
<widget class="QTreeWidget" name="treeWidget_3">
<property name="sizePolicy">
<sizepolicy hsizetype="Expanding" vsizetype="Minimum">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="frameShape">
<enum>QFrame::NoFrame</enum>
</property>
<property name="lineWidth">
<number>0</number>
</property>
<property name="verticalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="horizontalScrollBarPolicy">
<enum>Qt::ScrollBarAlwaysOff</enum>
</property>
<property name="sizeAdjustPolicy">
<enum>QAbstractScrollArea::AdjustToContents</enum>
</property>
<property name="autoScroll">
<bool>true</bool>
</property>
<property name="autoScrollMargin">
<number>0</number>
</property>
<attribute name="headerVisible">
<bool>false</bool>
</attribute>
<column>
<property name="text">
<string>1</string>
</property>
</column>
<item>
<property name="text">
<string>TreeWidget3</string>
</property>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
<item>
<property name="text">
<string>New Item</string>
</property>
</item>
</item>
</widget>
</item>
<item>
<spacer name="verticalSpacer">
<property name="orientation">
<enum>Qt::Vertical</enum>
</property>
<property name="sizeHint" stdset="0">
<size>
<width>17</width>
<height>82</height>
</size>
</property>
</spacer>
</item>
</layout>
</widget>
</widget>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menubar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>241</width>
<height>24</height>
</rect>
</property>
</widget>
<widget class="QStatusBar" name="statusbar"/>
</widget>
<resources/>
<connections>
<connection>
<sender>treeWidget</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget_2</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>33</x>
<y>42</y>
</hint>
<hint type="destinationlabel">
<x>31</x>
<y>172</y>
</hint>
</hints>
</connection>
<connection>
<sender>treeWidget</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget_3</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>94</x>
<y>76</y>
</hint>
<hint type="destinationlabel">
<x>43</x>
<y>271</y>
</hint>
</hints>
</connection>
<connection>
<sender>treeWidget_2</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>95</x>
<y>179</y>
</hint>
<hint type="destinationlabel">
<x>91</x>
<y>112</y>
</hint>
</hints>
</connection>
<connection>
<sender>treeWidget_2</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget_3</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>122</x>
<y>188</y>
</hint>
<hint type="destinationlabel">
<x>137</x>
<y>280</y>
</hint>
</hints>
</connection>
<connection>
<sender>treeWidget_3</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>193</x>
<y>296</y>
</hint>
<hint type="destinationlabel">
<x>167</x>
<y>115</y>
</hint>
</hints>
</connection>
<connection>
<sender>treeWidget_3</sender>
<signal>currentItemChanged(QTreeWidgetItem*,QTreeWidgetItem*)</signal>
<receiver>treeWidget_2</receiver>
<slot>clearSelection()</slot>
<hints>
<hint type="sourcelabel">
<x>217</x>
<y>295</y>
</hint>
<hint type="destinationlabel">
<x>217</x>
<y>226</y>
</hint>
</hints>
</connection>
</connections>
</ui>
A relevant piece of the translated code from the ui-form:
centralwidget = new QWidget(MainWindow);
centralwidget->setObjectName(QStringLiteral("centralwidget"));
verticalLayout = new QVBoxLayout(centralwidget);
verticalLayout->setSpacing(0);
verticalLayout->setObjectName(QStringLiteral("verticalLayout"));
verticalLayout->setSizeConstraint(QLayout::SetMinimumSize);
verticalLayout->setContentsMargins(0, 0, 0, 0);
scrollArea = new QScrollArea(centralwidget);
scrollArea->setObjectName(QStringLiteral("scrollArea"));
QSizePolicy sizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
sizePolicy.setHorizontalStretch(0);
sizePolicy.setVerticalStretch(0);
sizePolicy.setHeightForWidth(scrollArea->sizePolicy().hasHeightForWidth());
scrollArea->setSizePolicy(sizePolicy);
scrollArea->setStyleSheet(QStringLiteral("background-color: rgb(255, 255, 255);"));
scrollArea->setFrameShape(QFrame::NoFrame);
scrollArea->setLineWidth(0);
scrollArea->setWidgetResizable(true);
scrollAreaWidgetContents = new QWidget();
scrollAreaWidgetContents->setObjectName(QStringLiteral("scrollAreaWidgetContents"));
scrollAreaWidgetContents->setGeometry(QRect(0, 0, 241, 480));
verticalLayout_2 = new QVBoxLayout(scrollAreaWidgetContents);
verticalLayout_2->setSpacing(10);
verticalLayout_2->setObjectName(QStringLiteral("verticalLayout_2"));
verticalLayout_2->setContentsMargins(0, 0, 0, 0);
treeWidget = new QTreeWidget(scrollAreaWidgetContents);
QTreeWidgetItem *__qtreewidgetitem = new QTreeWidgetItem(treeWidget);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
new QTreeWidgetItem(__qtreewidgetitem);
QTreeWidgetItem *__qtreewidgetitem1 = new QTreeWidgetItem(__qtreewidgetitem);
QTreeWidgetItem *__qtreewidgetitem2 = new QTreeWidgetItem(__qtreewidgetitem1);
new QTreeWidgetItem(__qtreewidgetitem2);
treeWidget->setObjectName(QStringLiteral("treeWidget"));
QSizePolicy sizePolicy1(QSizePolicy::Expanding, QSizePolicy::Minimum);
sizePolicy1.setHorizontalStretch(0);
sizePolicy1.setVerticalStretch(0);
sizePolicy1.setHeightForWidth(treeWidget->sizePolicy().hasHeightForWidth());
treeWidget->setSizePolicy(sizePolicy1);
treeWidget->setFrameShape(QFrame::NoFrame);
treeWidget->setLineWidth(0);
treeWidget->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
treeWidget->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
treeWidget->setSizeAdjustPolicy(QAbstractScrollArea::AdjustToContents);
treeWidget->setAlternatingRowColors(false);
treeWidget->setUniformRowHeights(false);
treeWidget->setAnimated(false);
treeWidget->setHeaderHidden(true);
treeWidget->header()->setVisible(false);
verticalLayout_2->addWidget(treeWidget);
//... (other tree-widgets inserted)
verticalSpacer = new QSpacerItem(17, 82, QSizePolicy::Minimum, QSizePolicy::Expanding);
verticalLayout_2->addItem(verticalSpacer);
scrollArea->setWidget(scrollAreaWidgetContents);
verticalLayout->addWidget(scrollArea);
MainWindow->setCentralWidget(centralwidget);