How do I open a new window by click a button in the drop-down menu?

[ChoiHyebin]

Hello, I have a question. How do I open a new window or dialog by click a button in the drop-down menu? Please let me know. Thank you.

[KROIA]

Hello ChoiHyebin

This is not very difficult.
I will show it to you with the example included in this repo.

First, you need a Widged you want to show. I will not explain how this works because this is independend on your question.
What you need is the click event of the dropdown menue in your picture.

In the Example we have already such a menue.

// Code from example/mainwindow.cpp
// Add dropdown menu to button
  openFileButton->setPopupMode(QToolButton::MenuButtonPopup);
  QMenu *menu = new QMenu("Title");
  //menu->addAction(QIcon(":/icons/folder_2.svg"),
  //                "Recent directory");
  menu->addAction(QIcon(":/icons/file_2.svg"), "Recent file 1");
  menu->addAction(QIcon(":/icons/file_2.svg"), "Recent file 2");
  menu->addAction(QIcon(":/icons/file_2.svg"), "Recent file 3");
  openFileButton->setMenu(menu);

 // Now we will get the previously added actions.
  QList<QAction*> actions = menu->actions(); // Whis will get the Actions
 // I don't know why but in my Test the list contained 4 Elements which doesen't make sense for me because there were only 3 added...
 // Anyway, i added the debug here to check which QAction is which.
  qDebug() << actions[0]->text();
  qDebug() << actions[1]->text();
  qDebug() << actions[2]->text();

 // Now your importent part, use the QAction pointer to connect the "triggered" signal to your widged/window to open.
 // I tested it by simply hide this window (doesn't make sense but for the test its fine)
  connect(menu->actions()[0],&QAction::triggered,this,&MainWindow::hide);

I hope this helped you. =)