QTimer常用的几种写法：
1、SingleShot：只发送一次timeout信号
QTimer *timer = new QTimer(this); timer->setSingleShot(true); connect(timer, SIGNAL(timeout()), this, SLOT(update())); timer->start();
2、默认时间间隔为0，不停的发送信号timeout
QTimer *timer = new QTimer(this); connect(timer, SIGNAL(timeout()), this, SLOT(update())); timer->start();
3、setInterval：相隔指定时间后，发一次信号timeout
QTimer *timer = new QTimer(this); timer->setInterval(3000); connect(timer,SIGNAL(timeout()),this,SLOT(print())); timer->start();
4、start(std::chrono::milliseconds msec)：相隔指定时间后，发一次信号timeout，执行效果同3
QTimer *timer = new QTimer(this); connect(timer,SIGNAL(timeout()),this,SLOT(print())); timer->start(3000);
原文：https://www.cnblogs.com/qiang-upc/p/12782078.html