2020-9-23 use of QT timer qtimer class.

stay Qt There are two ways to use timers in , One is to use QObiect Class timer ; One is to use QTimer class .
The accuracy of timers depends on the operating system and hardware , Most platforms support 20ms The accuracy of .

■、QObject Class timer
QObject It's all Qt Object's base class , It provides a basic timer . adopt QObject::startTimer(), A time interval of one millisecond can be used as a parameter to start the timer , This function returns a unique integer timer identifier . This timer starts at every time interval " Trigger ", Until the timer identifier is explicitly used to call QObject::killTimer() end .
When the timer is triggered , The application will send a QTimerEvent. In the event loop , The processor processes timer events in the order of the event queue . When the processor is busy processing other events , The timer can't handle it immediately .
QObject Class also provides the function of timing . Timer related member functions are ：startTimer()、timeEvent()、killTimer().

QObject In the base class startTimer() and timerEvent() The prototype and description are as follows ：

int QObject::startTimer(int interval);

Start a timer and return to the timer ID, If you can't start a timer , Will return 0. After the timer starts , every other interval The millisecond interval will trigger a timeout event , until killTimer() Called to delete the timer . If interval by 0, Then there is no window system event processing every time the timer event occurs .

virtual void QObject::timerEvent(QTimerEvent *event);

Virtual functions timerEvent() Overloaded to implement the user's timeout event handler . If more than one timer is running ,QTimerEvent::timerId() Used to find the specified timer , Operate on it .
When a timer event occurs , Virtual functions timerEvent() With QTimerEvent The event parameter class is called together , Overload this function to get timer events .

The usage of timer is as follows ：

// The header file
class QNewObject : public QObject
{
Q_OBJECT
public:
QNewObject( QObject * parent = 0 );
virtual ~QNewObject();

protected:
void timerEvent( QTimerEvent *event );
int m_nTimerId;
};

// Source file
QNewObject::QNewObject( QObject * parent )
:QNewObject( parent )
{
m_nTimerId = startTimer(1000);
}

QNewObject::~QNewObject()
{
if ( m_nTimerId != 0 )
killTimer(m_nTimerId);
}

void QNewObject::timerEvent( QTimerEvent *event )
{
qDebug( "timer event, id %d", event->timerId() );
}

 

■、 Timer class QTimer
Timer class QTimer Provide a timer that transmits a signal when the timer is triggered , It provides a timeout event that triggers only once , The usual usage is as follows ：

// Create timer
QTimer *testTimer = new QTimer(this);
// Connect the timer timeout signal to the slot ( Function function ) Connect
connect( testTimer, SIGNAL(timeout()), this, SLOT(testFunction()) );
// Start running timer , The timing interval is 1000ms
testTimer->start(1000);
...
// Stop the timer
if ( testTimer->isActive() )
testTimer->stop();

QTimer It also provides a simple function with only one timing singleShot().
A timer is 100ms Post trigger handler animateTimeout() And trigger only once . The code is as follows ：

QTimer::singleShot( 100, this, SLOT(animateTimeout()) );

 

The second introduction ：

The use of timer is very simple , We only need the following steps to complete the application of timer ：
1. Generate a timer
QTimer *time_clock=new QTimer（parent）;
2. Connect the signal and slot of this timer , Using a timer timeout()
connect(time_clock,SIGNAL(timeout()),this,SLOT(slottimedone()));
That is, it will be sent when the timing time comes timeout() The signal , triggering slottimedone() Slot to finish something
3. Start timer , And set the timing period
There are two kinds of timer timing ：start(int time) and setSingleShot(true)
among start(int time) Yes means every time Seconds will restart the timer , The trigger timing can be repeated , Unless you use stop() Turn off the timer .
and setSingleShot(true) Only start the timer once
The former is often used in our projects .
time_clock->start(2000);
remarks : The usage of timer I found on the Chinese official website is in the following format ：
QTimer *timer = new QTimer( myObject );
connect( timer, SIGNAL(timeout()), myObject, SLOT(timerDone()) );
timer->start( 2000, TRUE ); // 2 Second single trigger timer
About the last sentence ,timer->start( 2000, TRUE ); In my practical application , add TRUE The compiler will report an error , do not know why , It doesn't matter if you remove it . This problem remains , Maybe it can be solved later