Gui: Add ScrollArea to Preferences

This adds QScrollArea widget to DlgPreferences which in turn allows
preference pages to be scrollable. Stacked widget sizes are forced to
selected widget so scroll area should appear when it is needed.

Fixes #11511

src/Gui/DlgPreferencesImp.cpp

@@ -114,6 +114,10 @@ DlgPreferencesImp::DlgPreferencesImp(QWidget* parent, Qt::WindowFlags fl)
             &QPushButton::clicked,
             this,
             &DlgPreferencesImp::showResetOptions);
+    connect(ui->groupWidgetStack,
+            &QStackedWidget::currentChanged,
+            this,
+            &DlgPreferencesImp::onStackWidgetChange);
 
     ui->groupsTreeView->setModel(&_model);
     
@@ -193,6 +197,15 @@ PreferencesPageItem* DlgPreferencesImp::createGroup(const std::string &groupName
     auto groupPages = new QStackedWidget;
     groupPages->setProperty(GroupNameProperty, QVariant(groupNameQString));
 
+    connect(groupPages,
+            &QStackedWidget::currentChanged,
+            this,
+            &DlgPreferencesImp::onStackWidgetChange);
+
+
+    if (ui->groupWidgetStack->count() > 0) {
+        groupPages->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
+    }
     ui->groupWidgetStack->addWidget(groupPages);
 
     auto item = new PreferencesPageItem;
@@ -255,6 +268,11 @@ void DlgPreferencesImp::createPageInGroup(PreferencesPageItem *groupItem, const
         page->loadSettings();
 
         auto pages = qobject_cast<QStackedWidget*>(groupItem->getWidget());
+
+        if (pages->count() > 0) {
+            page->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
+        }
+
         pages->addWidget(page);
     }
     catch (const Base::Exception& e) {
@@ -637,7 +655,6 @@ void DlgPreferencesImp::restartIfRequired()
 
 void DlgPreferencesImp::showEvent(QShowEvent* ev)
 {
-    this->adjustSize();
     QDialog::showEvent(ev);
 }
 
@@ -668,6 +685,20 @@ void DlgPreferencesImp::onPageSelected(const QModelIndex& index)
     updatePageDependentLabels();
 }
 
+void DlgPreferencesImp::onStackWidgetChange(int index)
+{
+    auto stack = qobject_cast<QStackedWidget*>(sender());
+
+    for (int i = 0; i < stack->count(); i++) {
+        auto current = stack->widget(i);
+        current->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
+    }
+
+    if (auto selected = stack->widget(index)) {
+        selected->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
+    }
+}
+
 void DlgPreferencesImp::changeEvent(QEvent *e)
 {
     if (e->type() == QEvent::LanguageChange) {