Timer.h

#pragma once
#include <QFont>
#include <QFrame>
#include <QLabel>
#include <QMainWindow>
#include <QPushButton>
#include <QTimer>

namespace Examples {
  class Window1 : public QMainWindow {
    Q_OBJECT
  public:
    Window1() {
      label.setText(QString::number(static_cast<double>(counter) / 10, 'f', 1));
      label.move(10, 10);
      label.resize(210, 70);
      label.setFont(QFont("Arial", 64, QFont::Normal, true));
      QPalette palette;
      palette.setColor(QPalette::WindowText, QColor::fromRgb(30, 144, 255));
      label.setPalette(palette);

      button.setText("Start");
      button.move(10, 90);
      connect(&button, &QPushButton::clicked, [&] {
        if (timer.isActive())
          timer.stop();
        else
          timer.start();
        button.setText(timer.isActive() ? "Stop" : "Start");
       });

      timer.setInterval(100);
      connect(&timer, &QTimer::timeout, [&] {
        label.setText(QString::number(static_cast<double>(++counter) / 10, 'f', 1));
      });

      setCentralWidget(&frame);
      setWindowTitle("Timer example");
      resize(230, 130);
    }

  private:
    QFrame frame;
    QLabel label {&frame};
    QPushButton button {&frame};
    QTimer timer {this};
    int counter = 0;
  };
}