main_rs.cpp

#include <QAction>
#include <QApplication>
#include <QLineEdit>
#include <QMenu>
#include <QMessageBox>
#include <QPushButton>
#include <QTableWidget>
#include <QVBoxLayout>

struct Form : QWidget {
  Form() {
    button.setEnabled(false);

    table.setContextMenuPolicy(Qt::ContextMenuPolicy::CustomContextMenu);
    table.setRowCount(2);
    table.setColumnCount(1);

    auto item1 = new QTableWidgetItem;
    item1->setText("Item 1");
    table.setItem(0, 0, item1);
    auto item2 = new QTableWidgetItem;
    item2->setText("Item 2");
    table.setItem(1, 0, item2);

    layout.addWidget(&line_edit);
    layout.addWidget(&button);

    layout.insertWidget(0, &table);

    show();
    init();
  }

  void init() {
    connect(&button, &QPushButton::clicked, this, [this] {
      const auto text = line_edit.text();
      QMessageBox::information(
          this, "Example", QString("Text: \"%1\". Congratulations!").arg(text));
    });

    connect(&line_edit, &QLineEdit::textEdited, this,
            [this] { button.setEnabled(!line_edit.text().isEmpty()); });

    connect(&table, &QTableWidget::currentItemChanged, this,
            [](QTableWidgetItem *current, QTableWidgetItem *previous) {
              if (previous) {
                auto font = previous->font();
                font.setBold(false);
                previous->setFont(font);
              }
              if (current) {
                auto font = current->font();
                font.setBold(true);
                current->setFont(font);
              }
            });
    connect(&table, &QTableWidget::customContextMenuRequested, this,
            &Form::on_table_context_menu_requested);
  }

  void on_table_context_menu_requested(QPoint pos) {
    auto global_pos = table.viewport()->mapToGlobal(pos);
    QMenu menu;
    menu.addAction("Fake action 1");
    menu.addAction("Fake action 2");

    QAction action3{"Real action"};
    menu.addAction(&action3);

    QAction *action = menu.exec(global_pos);
    auto message = [&]() -> QString {
      if (!action) {
        return "No action selected!";
      } else if (action == &action3) {
        return "Real action selected!";
      } else {
        return QString("Fake action selected (%1)").arg(action->text());
      }
    }();
    QMessageBox::information(this, "Example", message);
  }

  QVBoxLayout layout{this};
  QLineEdit line_edit;
  QPushButton button{"Start"};
  QTableWidget table;
};

int main(int argc, char *argv[]) {
  QApplication a(argc, argv);
  Form f;
  return a.exec();
}