Question

How I can do following: I’d like show my main window on start on the center screen.

Answer 1

You’ll need to setGeometry on your top-level widget before you show it. The easiest way I can think of to work out what geometry you need is via QDesktopWidget. Try the example below (create a QPushButton, press it while moving the widget around various screens) and you’ll see what I mean:

MainWindow::MainWindow(QWidget *parent) :
  QMainWindow(parent),
  ui(new Ui::MainWindow)
{   
  ui->setupUi(this);
  connect(ui->pushButton, SIGNAL(released()), this, SLOT(ButtonPressed()));
}

MainWindow::~MainWindow()
{
  delete ui;
}

void MainWindow::ButtonPressed()
{
  qDebug() << QApplication::desktop()->screenCount();
  qDebug() << QApplication::desktop()->screenNumber();
  qDebug() << QApplication::desktop()->screenGeometry(this);
}

Should be reasonably simple from there to come up with a generic version that works out a user’s center screen (if it exists).