How to use QTimer in Qt Creator to get data from an external peripheral device for a specific time interval only?

SHUBHAM SINGH RAO

Aim : I m working on Qt Creator and want to interface Modem with my main programme For that, I need fetch the data from modem for a specific time interval (say 3 seconds) only and after that I have to stop receiving data.

Present Status 05/11/18 :
I want to execute a blocking method through which I can wait (say 3 seconds) for data . If I receive data in 3 seconds, I will move ahead for some another task else I will quit. Is there any method except threading?
I am trying to do it with QEventLoop but no success achieved so far.
Kindly suggest any helpful method or any relevant example?

My Work: I tried to implement it using

QTimer::singleShot(3000,this,SLOT(SLOT1()))

But the limitation with it: It calls the SLOT1 after 3000 msec, but this is not what I want.

My requirement is to use timer in order to fetch data for 3 seconds only and then stop.

aha_1980

@SHUBHAM-SINGH-RAO the question is: how do you fetch the data? in a loop? then QElapsedTimer could help you.

Or with signals? Then your SLOT() would stop the fetching.

As long as this is unclear, its hard to help.

aha_1980

also, how is that question different from: https://forum.qt.io/topic/96190/timer-problem ?

SHUBHAM SINGH RAO

@aha_1980 i m giving a detailed explanation of my problem in this post

aha_1980

@SHUBHAM-SINGH-RAO

this is no reason to create a new topic
important information is still missing

SGaist

Hi,

To add to @aha_1980, you can edit your post and add the missing information there. Click on the icon with the vertical three points.

SHUBHAM SINGH RAO

@SGaist I have edited my present status in my Question..kindly look at it!

SHUBHAM SINGH RAO

@aha_1980 @SGaist I have edited my present status in my Question..kindly look at it!

aha_1980

@SHUBHAM-SINGH-RAO there is no way outside the blockin method. the timeout has to be implemented within that method.

Sorry, but if you don't show some relevant code, thats all I can tell you.

Regards

SHUBHAM SINGH RAO

@aha_1980 I am attaching a similar code to test concept
I have used network access manager but I want to take serial data instead.

mainwindow.cpp

void MainWindow::on_pushButton_clicked()
{
ui->label_2->setText("Clear replies ");
if(value==0)
{
ui->label->setText("clicked");
value=1;
}
else if(value==1)
{

    ui->label->setText("unclicked");
    value=0;
}

somefunction();

}

void MainWindow::somefunction()
{
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
QEventLoop loop;
QTimer timer;

timer.setSingleShot(true);
connect(&timer, SIGNAL(timeout()), &loop, SLOT(quit()));
connect(manager, SIGNAL(finished(QNetworkReply*)), &loop, SLOT(quit()));

timer.start(10000);
manager->get(QNetworkRequest(QUrl("http://www.google.com")));
loop.exec();

if (timer.isActive())
{
     ui->label_2->setText("Reply recieved");
}
else
ui->label_2->setText("No reply from client");

}

void MainWindow::on_pushButton_2_clicked()
{
if(value2==0)
{
ui->label_3->setText("clicked");
value2=1;
}
else if(value2==1)
{

    ui->label_3->setText("unclicked");
    value2=0;
}

}

mainwindow.ui

aha_1980

@SHUBHAM-SINGH-RAO said in How to use QTimer in Qt Creator to get data from an external peripheral device for a specific time interval only?:

timer.start(10000);
manager->get(QNetworkRequest(QUrl("http://www.google.com")));
loop.exec();

Don't do this! Local event loops are advanced stuff, and can easily lead to problems.

Use QNetworkRequest as it is designed with signals&slots. In your timeout slot, you can close() or abort() the QNetworkReply, like described here: https://stackoverflow.com/questions/14535502/how-to-stop-qnetworkaccessmanager-from-getting-a-reply-c