How to display the result of an operation in incremental fashion strating from 0?

[Santhoshpl]

@jsulm Yes, you are right. I am seeing only the end result after the loop exits.
I want to update the UI as it runs. The ui->product->display(product) displays the result in the UI.

[JonB]

@Santhoshpl So try @LeLev's suggested code.

[Santhoshpl]

@LeLev Thank you for the solution, but its crashing.
The error message displayed is:
The program has unexpectedly finished.
The process was ended forcefully.
productApplication.exe is crashed

[ODБOï]

@Santhoshpl said in How to display the result of an operation in incremental fashion strating from 0?:

crash

can you please show your code ?

[Gerd]

or..
just add a
QApplication::processEvents();

right after

ui->product->display(temp);

[Santhoshpl]

@LeLev please find the below code:

void MainWindow::on_controlButton_clicked()
{
double num1 = ui->num1->value();
double num2 = ui->num2->value();
double product = num1 * num2;
double currentDisplay=0;
QTimer *timer = new QTimer();
QObject::connect(timer, &QTimer::timeout,&{
if(currentDisplay>=product){
timer->stop();
}
ui->product->display(currentDisplay);
QApplication::processEvents();
if(currentDisplay<meetingCost)currentDisplay++;
});
timer->start(500);
}
}

[JonB]

@Santhoshpl
It helps others if you put literal code in this forum's code markers.

Meanwhile, I don't know, @Lelev writes

 QObject::connect(timer, &QTimer::timeout,[&](){

while you write

QObject::connect(timer, &QTimer::timeout,&{

so do you know what you're doing there with your lambda? Is there any reason you change his code for this?

Otherwise run under debugger and look at the context/stack trace when the crash occurs.

[Christian Ehrlicher]

@JonB said in How to display the result of an operation in incremental fashion strating from 0?:

[&]

Please take a c++ book about lambdas - you're passing by reference and it will therefore go out of scope...

[jsulm]

@Gerd said in How to display the result of an operation in incremental fashion strating from 0?:

QApplication::processEvents();

This is an ugly work-around and should be avoided. It is better to program in asynchronous way instead of calling processEvents().

[Gerd]

lol
then you should tell the qt people to remove such examples from the examples in qt sources...

[J.Hilk]

@Gerd said in How to display the result of an operation in incremental fashion strating from 0?:

then you should tell the qt people to remove such examples from the examples in qt sources...

you're right, it shouldn't be there, can you name/link such an example?

[Gerd]

Qt\5.12.6.src\qtbase\examples\widgets\dialogs\findfiles
Qt\5.12.6.src\qtbase\examples\widgets\itemviews\pixelator
Qt\5.12.6.src\qtbase\examples\widgets\painting\fontsampler

[JonB]

@Gerd Can you supply these as clickable links to the on-line docs?

[Gerd]

heres one of them:
findfiles

[Gerd]

for these it isnt in the doc pages but in the sourcecode..
pixelator
fontsampler

[J.Hilk]

@Gerd
Well these examples haven't been touched in years, are very basic but never the less badly designed.

One can redesign those examples, without the need for a processEvent calls, which will make them bigger (source code size).
But IMHO that's something that should be done.

[Colins2]

@LeLev
I just read your response and it seemed what I need as well.
However, I just get a crash with this code:

I have been having the same problems as the OP (and everyone else, I guess)
This code snippet is just for testing messages written to a QPlainTextEdit widget, nothing else.

void MainWindow::writeLeft()
{
    int32_t cnt = 100;
    QString msg, cno;
    QTimer *ltimer = new QTimer();

    do{
        QTextStream(&cno) << cnt;
        msg = ("Hello left no : "+ cno);
        //message has been constructed, stop the process and display it
        QObject::connect(ltimer, &QTimer::timeout,[&](){
            if(cnt > 0){
                ltimer->stop();
            }
        ui->memo1->appendPlainText(msg);
        });
        cno.clear();
        QThread::sleep(1);
        ltimer->start(10);
        cnt--;
    }while(cnt > 0);
}

If I remove the QTimer statements then I just get the whole lot dumped to the QPlainTextEdit in one go.

[JonB]

@Colins2
You are re-connecting the timer every time round the loop?

[ODБOï]

@Colins2 im not 100% sure what you need to do but see

    int32_t cnt = 100;
    QString msg, cno;
    QTimer *ltimer = new QTimer();

    //do{
    // QTextStream(&cno) << cnt;

    //msg = ("Hello left no : "+ cno);

    QObject::connect(ltimer, &QTimer::timeout,[&](){
        cnt--;
        if(cnt == 0){ // <
            ltimer->stop();
        }
        qDebug()<< ("Hello left no : " + QString::number(cnt));

    });

    cno.clear();
    //  QThread::sleep(1);
    ltimer->start(10);

    //   }while(cnt > 0);

[JonB]

@Colins2
Glancing only at @LeLev's latest post, this makes much more sense. Give it a go?!