Gui: by default restore the last visited page in the preferences dialog

See also: https://forum.freecad.org/viewtopic.php?t=77071

src/Gui/CommandStd.cpp

@@ -370,8 +370,19 @@ Action * StdCmdDlgPreferences::createAction()
 void StdCmdDlgPreferences::activated(int iMsg)
 {
     Q_UNUSED(iMsg);
+
+    static QString groupName{};
+    static int index{};
+
     Gui::Dialog::DlgPreferencesImp cDlg(getMainWindow());
-    cDlg.exec();
+    ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences");
+    if (hGrp->GetBool("RestoreGroupPage", true)) {
+        cDlg.activateGroupPage(groupName, index);
+    }
+
+    if (cDlg.exec()) {
+        cDlg.activeGroupPage(groupName, index);
+    }
 }
 
 //===========================================================================

src/Gui/DlgPreferencesImp.cpp

@@ -305,13 +305,30 @@ void DlgPreferencesImp::activateGroupPage(const QString& group, int index)
         QListWidgetItem* item = ui->listBox->item(i);
         if (item->data(GroupNameRole).toString() == group) {
             ui->listBox->setCurrentItem(item);
-            auto tabWidget = static_cast<QTabWidget*>(ui->tabWidgetStack->widget(i));
-            tabWidget->setCurrentIndex(index);
-            break;
+            auto tabWidget = dynamic_cast<QTabWidget*>(ui->tabWidgetStack->widget(i));
+            if (tabWidget) {
+                tabWidget->setCurrentIndex(index);
+                break;
+            }
         }
     }
 }
 
+/**
+ * Returns the group name \a group and position \a index of the active page.
+ */
+void DlgPreferencesImp::activeGroupPage(QString& group, int& index) const
+{
+    int row = ui->listBox->currentRow();
+    auto item = ui->listBox->item(row);
+    auto tabWidget = dynamic_cast<QTabWidget*>(ui->tabWidgetStack->widget(row));
+
+    if (item && tabWidget) {
+        group = item->data(GroupNameRole).toString();
+        index = tabWidget->currentIndex();
+    }
+}
+
 void DlgPreferencesImp::accept()
 {
     this->invalidParameter = false;

src/Gui/DlgPreferencesImp.h

@@ -123,7 +123,8 @@ public:
 
     void accept() override;
     void reload();
-    void activateGroupPage(const QString& group, int id);
+    void activateGroupPage(const QString& group, int index);
+    void activeGroupPage(QString& group, int& index) const;
 
 protected:
     void changeEvent(QEvent *e) override;