Low performance, timer and label.

[Loc888]

@VRonin Ther is nothing to post, simple Qtimer and settext function. That's it.
The timer refire the function, and set the current time.

[VRonin]

Can you try this basic example?

#include <QApplication>
#include <QTimer>
#include <QLabel>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel mainWid;
    QTimer mainTimer;
    int counter = 0;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid,&counter]()->void{
        mainWid.setText(QObject::tr("%1 sec").arg(++counter));
    });
    mainTimer.start(1000);
    mainWid.show();
    return a.exec();
}

[Loc888]

@VRonin It says no matching function.

[VRonin]

@Loc888 I tested it on my machine Qt 5.10 MSVC2013 x64 Win7. What version of Qt are you running?

[Loc888]

@VRonin Desktop Qt 5.2.0 MinGW 32bit

[VRonin]

Then everything should work, you probably just have to enable C++11

• add CONFIG += c++11 in your .pro file
• re-run qmake

[Loc888]

@VRonin It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

[J.Hilk]

@Loc888 I think you need to be a bit more specific, with what is going on.

It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

Updating a QLabel's text shouldn't take seconds to update

to modify the code of @VRonin abit to display time and fast changes:

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid]()->void{
       mainWid.setText(QTime::currentTime().toString("hh.mm.ss.zz"));
    });
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

[Loc888]

@J.Hilk I would like to use that, but i don't want current time, i want everything starting from 0.

[J.Hilk]

@Loc888
this code examples are for the purpose of trouble shooting.
But it's easy enought to adapt.

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>
#include <QElapsedTimer>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QTime time(0,0);
    QElapsedTimer actualTimePassed;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid, &time, &actualTimePassed]()->void{
        time = time.addMSecs(actualTimePassed.elapsed());
        actualTimePassed.start();
        mainWid.setText(time.toString("hh.mm.ss.zzz"));
    });
    actualTimePassed.start();
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

[VRonin]

@Loc888 said in Low performance, timer and label.:

it's working, but i need it in MS

Unfortunately this is platform dependant. Best you could do is:

#include <QApplication>
#include <QTimer>
#include <QLabel>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel mainWid;
    QTimer mainTimer;
    mainTimer.setTimerType(Qt::PreciseTimer);
    unsigned int counter = 0;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid,&counter]()->void{
        mainWid.setText(QObject::tr("%1 msec").arg(++counter));
        mainWid.repaint();
    });
    mainTimer.start(1);
    mainWid.show();
    return a.exec();
}

Please note, from http://doc.qt.io/qt-5/qt.html#TimerType-enum:

Precise timers try to keep millisecond accuracy

try != will, unfortunately

[Loc888]

@VRonin Maybe i expressed wrong, but i don't want it in Ms (the total), so 5500 = 5,5s, i want that pattern "mm.ss.zzz" or "mm.ss.zz" , but i want it to start from 0, not from the current time. Is any way to force it? (In sec, ther is no delay when the method update the text).

[Loc888]

@J.Hilk Guys,i tried J.Hilk code,and it's not working how it should.

It doesnt help me, it's working, but if i compare the timer to my windows time, the difference is arround 10s (after 2min test), it's too mutch.

Why it's happening?

Ps. I tried with "setTimerType(Qt::PreciseTimer);", but still doesn't help...

????????

[mpergand]

My turn ;)

QLabel label;
label.setGeometry(100,100,200,50);
 QTimer timer;
 QTime time;

 QObject::connect(&timer,&QTimer::timeout,[&time,&label](){
    QTime elapsed=QTime::fromMSecsSinceStartOfDay(time.elapsed());
    label.setText(elapsed.toString("mm:ss:zzz"));
    });

time.start();
timer.start(100);
label.show();

[Loc888]

@mpergand

It seems you are the winner... Why it's working?

I thought it's working, because you set the delay to 100ms, but even if i change it to 1ms, still working 100%.
I don't understand why this is working,and the other timers including my, are all retarded... Why it's happening?

And that's the text update method fault's, i tried to turn off the update, and just set the last result, and it's 100% accurate.

[mpergand]

I know by experience that to rely on a timer is all wrong.
You must rely on the system clock for good accuracy.

And that's the text update method fault's, i tried to turn off the update, and just set the last result, and it's 100% accurate.

Refresh 1000 times per sec is a heavy task, it consumes about 20% cpu on my machine and serves nothing.
Timers use the event loop and if the computer is doing heavy tasks, timers triggers might be lost.
Rely on event loops for a counter is definitely a bad idea.

[Loc888]

@mpergand Ok, how i can use it with Start, Stop, and Reset button? Because i am trying to move your code to another project, and work with buttons, but when i start the timer, it doesn't do anything.. Still be on 00:00:000, i run it ones, and it start from the actual minutes and seconds, then i modified your code to force it start from 0, and i broke something, now nothing is working...

[Loc888]

@mpergand Ok, nevermind, i am blind sometimes... I fix it.

I find the way to restart it, but i have some problems with

" time.fromString("05:00:000"); "

It's not working, how should i use that? Or how to stop the time and the timer, and re-start it again but from the last time? (I dont want to reset it when i press the stop button, and then start).

[VRonin]

You missed an argument and the fact that it's a static function: http://doc.qt.io/qt-5/qtime.html#fromString-1

time = QTime::fromString("05:00:000","mm:ss:zzz");

Have you considered QTimeEdit instead of QLabel?

[Loc888]

@VRonin Still reset when i press the start button, and when i stop and start,it starts from 0.
Comon, how to fix that? It's almost fixed.