Qt dialog not showing its widgets - c++

Question

I would like to create custom QT dialog (non-modal). Problem with my implementation is that it shows only dialog window with title, and no widgets that I've added to it.
Code below (I've ommited most of it, added just dialog and main window parts).
MainWindow.h
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
/// some other stuff
private:
std::unique_ptr<ui::DialogAddUpdateItem> addItemDialog;
/// some other stuff
}
MainWindow.cpp
/// some stuff
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
/// some stuff
addItemButton = new QPushButton(tr("Add item"));
QObject::connect(addItemButton, &QPushButton::pressed, this, &MainWindow::openAddItemDialog);
navLay->addWidget(addItemButton);
addItemDialog = make_unique<ui::DialogAddUpdateItem>(this);
/// some stuff
}
void MainWindow::openAddItemDialog() {
addItemDialog->show();
//addItemDialog->raise(); does not work with or without those functions
//addItemDialog->activateWindow();
//QApplication::processEvents();
}
DialogAddUpdateItem.h
namespace ui {
class DialogAddUpdateItem : public QDialog
{
Q_OBJECT
public:
DialogAddUpdateItem(QWidget *parent = nullptr);
private:
QPushButton *buttonAcc, *buttonRevert, *buttonCancel;
QGroupBox *centralWidget, *buttonsWidget;
QLabel *labelName, *labelDescription;
QLineEdit *textName;
QPlainTextEdit *textDescription;
}
}
DialogAddUpdateItem.cpp
namespace ui {
DialogAddUpdateItem::DialogAddUpdateItem(QWidget *parent) : QDialog(parent)
{
if (!item) {
setWindowTitle(tr("New object"));
}
centralWidget = new QGroupBox;
QHBoxLayout *itemLay = new QHBoxLayout;
centralWidget->setLayout(itemLay);
labelName = new QLabel(tr("Name"));
itemLay->addWidget(labelName);
textName = new QLineEdit;
if (item) {
textName->setText(QString::fromStdString(item->getName()));
}
itemLay->addWidget(textName);
labelDescription = new QLabel(tr("Description"));
if (item) {
textDescription = new QPlainTextEdit(QString::fromStdString(item->getDescription()));
} else {
textDescription = new QPlainTextEdit;
}
itemLay->addWidget(textDescription);
buttonAcc = new QPushButton(tr("Save"));
buttonAcc->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
QObject::connect(buttonAcc, &QPushButton::clicked, this, &DialogAddUpdateItem::acceptItem);
buttonRevert = new QPushButton(tr("Revert"));
buttonRevert->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
QObject::connect(buttonRevert, &QPushButton::clicked, this, &DialogAddUpdateItem::revertItem);
buttonCancel = new QPushButton(tr("Cancel"));
buttonCancel->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
QObject::connect(buttonCancel, &QPushButton::clicked, this, &DialogAddUpdateItem::cancelItem);
buttonsWidget = new QGroupBox;
itemLay->addWidget(buttonsWidget);
QVBoxLayout *buttonsLay = new QVBoxLayout;
buttonsLay->addWidget(buttonAcc);
buttonsLay->addWidget(buttonRevert);
buttonsLay->addWidget(buttonCancel);
}
}

Answer 1

In DialogAddUpdateItem.cpp the centralWidget has no parent, therefore it is not bound to anything and therefore not displayed. You should modify this:
centralWidget = new QGroupBox;
into this:
centralWidget = new QGroupBox(this);
Now the DialogAddUpdateItem will be the parent of the centralWidget and it should display it.
Also it seems like You are leaving some other widgets without a parent - it might cause trouble. For example the QLineEdit textName has this issue.