注意事项：
1、QTimer's accuracy depends on the underlying operating system and hardware.Most platforms support an accuracy of 20 milliseconds; some provide more.
2、If Qt is unable to deliver the requested number of timer events, it will silently discard some.
问题：当开启一个定时器，设置时间间隔为50ms，它对应的QTimerEvnet处理函数要执行一段耗时的操作，如何让界面快速响应用户的鼠标事件呢
代码：
#include "QtGuiApplication2.h"
#include <QDebug>
#include <QTimerEvent>
#include <QDateTime>
#include <QTime>
#include <QThread> QtGuiApplication2::QtGuiApplication2(QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);
startTimer();
connect(ui.pushButton, &QPushButton::clicked, this, &QtGuiApplication2::showCurrentTime);
} void QtGuiApplication2::timerEvent(QTimerEvent *event)
{
//QThread::msleep(2000);这个和下面的效果是一样的
QTime qTime1 = QTime::currentTime();
while (qTime1.msecsTo(QTime::currentTime())<)
qDebug() << "do nothing just for test";
} void QtGuiApplication2::showCurrentTime()
{
ui.label->setText(QDateTime::currentDateTime().toString("hh:mm:ss.zzz"));
}
Ui:
当运行程序的时候，点击按钮发现textLabel的响应时间差不多是2秒，通过text显示的时间可以计算出来
解决方法：
void QtGuiApplication2::timerEvent(QTimerEvent *event)
{
//QThread::msleep(2000);
QTime qTime1 = QTime::currentTime();
while (qTime1.msecsTo(QTime::currentTime()) < ) {
QCoreApplication::processEvents(QEventLoop::AllEvents, );
qDebug() << "do nothing just for test";
} }
这个解决了操作耗时的情况，但是当你选择QThread::msleep(2000);那怎么都会卡了
疑问：
假设当前时刻为0;程序开始运行；100ms时刻，我按下按钮；此时事件队列里面应该有QTimerEvent;QTimerEvent;QMousePress这三个事件要处理，按理说Label的时间相应应该是4s左右啊，可能的解释就是If Qt is unable to deliver the requested number of timer events, it will silently discard some.因此它丢弃了QMousePress之前相同的QTimerEvent
此实验验证了这个观念：
#include <QtWidgets/QDialog>
#include <QTime>
#include "ui_QtGuiApplication2.h" class QtGuiApplication2 : public QDialog
{
Q_OBJECT public:
QtGuiApplication2(QWidget *parent = Q_NULLPTR);
protected:
void timerEvent(QTimerEvent *event) override;
void showCurrentTime();
private:
Ui::QtGuiApplication2Class ui;
int id;
QTime lastTime;
};
QtGuiApplication2::QtGuiApplication2(QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);
startTimer();
id = startTimer();
lastTime = QTime::currentTime();
} void QtGuiApplication2::timerEvent(QTimerEvent *event)
{
qDebug() << "current timer id: " << event->timerId();
if (event->timerId() == id) {
ui.label->setText(QString::number(lastTime.msecsTo(QTime::currentTime())));
lastTime= QTime::currentTime();
}
}
通过界面的Label显示基本都是1014左右；多出来的14毫秒就是执行50msQTimerEvent的输出语句和 lastTime= QTime::currentTime()的总耗时；
因此可以推测出：
当有个定时器在事件队列里有很多个QTimerEvent;那么当有另外一个事件A到了，在执行完当前的QTimerEvent之后它会丢弃A之前其他QTimerEvent；直接执行事件A
所以14毫秒就是执行50msQTimerEvent的输出语句和 lastTime= QTime::currentTime()的总耗时