External process from Qml

[Naveen_D]

@p3c0 Sir i used execute instead of start but...i am not able to pass the output which i got from the new process, back to qml...what may be the problem ?
my code

#include "ProcessWidget.h"

ProcessWidget::ProcessWidget(QWidget *parent)
    : QWidget(parent)
{
}

void ProcessWidget::vStartProcess()
{
    qDebug()<<"entered the function"<<endl;
    const QString program = QStringLiteral("/home/ubuntu/Documents/Sample_Examples_Qt_Qml/VoiceRecognition/VoiceRecognition");
    myProcess = new QProcess;

    connect(myProcess,SIGNAL(readyReadStandardError()),this,SLOT(vEndProcess()));
    connect(myProcess,SIGNAL(finished(int)),myProcess,SLOT(deleteLater()));
    connect(this,&ProcessWidget::destroyed,myProcess,&QProcess::kill);
    myProcess->execute(program);
//    myProcess->waitForStarted(30000);
    qDebug()<<"process started waiting for output"<<endl;

}

void ProcessWidget::vEndProcess()
{
    const QString processOut = QString::fromLatin1(myProcess->readAllStandardError());
    qDebug()<<"output>>>>"<<processOut<<endl;
    const QRegularExpression regXp("Received Command:s*(.+)");
    const auto regXpMatch = regXp.match(processOut);
    if(regXpMatch.hasMatch()){
        qDebug() << "Output of regular exp is: "<< regXpMatch.captured(1);
        signalData= regXpMatch.captured(1);
        qDebug()<<"signal data is >>"<<signalData<<endl;
        emit playmusicsignal(signalData);
    }
}

ProcessWidget::~ProcessWidget()
{

}

in the above code, i didn't get any debug statements in console from vEndProcess function

[p3c0]

@Naveen_D Are you sure you want readyReadStandardError or readAllStandardOutput instead ?

[Naveen_D]

@p3c0

Are you sure you want readyReadStandardError or readAllStandardOutput instead ?

even when i use readAllStandardOutput i am not able to send the output through signal.

[VRonin]

Maybe I'm being silly here but since you are running what looks like the Hello Speak Example why do you start it as a separate process rather than a separate thread?

[Naveen_D]

@VRonin Sir i am not aware of threads...i am learning it from begining...for time being i am using separate process to get the required output.

[VRonin]

Try having a look at https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

[Naveen_D]

@VRonin thanks for the link sir..i will go through it...but can i know what i need to do with the process thing to get the required output.?

[VRonin]

That's because you block the event loop that you need to read. Use

void ProcessWidget::vStartProcess()
{
    qDebug()<<"entered the function"<<endl;
    const QString program = QStringLiteral("/home/ubuntu/Documents/Sample_Examples_Qt_Qml/VoiceRecognition/VoiceRecognition");
    myProcess = new QProcess;
QEventLoop blockLoop;
    connect(myProcess,SIGNAL(readyReadStandardError()),this,SLOT(vEndProcess()));
    connect(myProcess,SIGNAL(finished(int)),myProcess,SLOT(deleteLater()));
connect(myProcess,SIGNAL(finished(int)),&blockLoop,SLOT(quit()));
    connect(this,&ProcessWidget::destroyed,myProcess,&QProcess::kill);
    myProcess->start(program);
    qDebug()<<"process started waiting for output"<<endl;
blockLoop.exec();
}

[Naveen_D]

@VRonin Sir if i use the EventLoop it is not returning control...it will be in continuous loop like if i give input through live microphone it will wait for next input like that

[VRonin]

@Naveen_D said in External process from Qml:

but what is happening is..when i call the c++ function from qml, the control doesn't wait until the function is over, it continues to print some debug statements, which i have given after that function call

@Naveen_D said in External process from Qml:

if i use the EventLoop it is not returning control

I'm not sure I understand what you want to achieve. Do you want the process to act synchronously (loop until process is over) or asynchronously (return control almost immediately to the main app)?

[Naveen_D]

@VRonin the scenario is..when i call the c++ function from qml it should start the process...through which i get the output and will pass the output through a signal back to qml. till the process is not completed it should not return back to main app(i.e Qml app).
Now i am getting the output to my console but i am not able to send it as shown in the above code.

[jsulm]

@Naveen_D Why should it not return? What you are trying to do is not how Qt apps should work. You should use signals/slots: you start the process, connect signals/slots and as soon as there is input from the process you handle it in the slot.

[Naveen_D]

@jsulm Sorry sir i didn't get...is the above code wrong which i have posted ? or what changes i need to do ?

One more doubt..how to compare a string in Qml...like in Qt we do (str=="some string")

[jsulm]

@Naveen_D ProcessWidget::vStartProcess is currently blocking, why? Why not just start the process, connect signals/slots and return from ProcessWidget::vStartProcess ?

void ProcessWidget::vStartProcess()
{
    qDebug()<<"entered the function"<<endl;
    const QString program = QStringLiteral("/home/ubuntu/Documents/Sample_Examples_Qt_Qml/VoiceRecognition/VoiceRecognition");
    myProcess = new QProcess;
    connect(myProcess,SIGNAL(readyReadStandardError()),this,SLOT(vEndProcess()));
    connect(myProcess,SIGNAL(readyReadStandardOutput()),this,SLOT(processStandardOutput()));
    connect(myProcess,SIGNAL(finished(int)),myProcess,SLOT(deleteLater()));
    connect(this,&ProcessWidget::destroyed,myProcess,&QProcess::kill);
    myProcess->start(program);
}

processStandardOutput() will be called as soon as the process is writing something to standard output.

[Naveen_D]

@jsulm Yes i got that...
i want to know how to compare string s in Qml...
the string which i am passing through the signal...i want to compare that in qml and next give functionality for that...

i used the following code but didn't get...

onPlaymusicsignal: {
                    console.log("Recorded Voice :" + recordedString)
                    var receivedString = recordedString
                    console.log(receivedString)
                    if(receivedString == "GOTO MUSIC")
                    {
                        console.log("play music")
                    }
                    else
                    {
                        console.log("please try again")
                    }
                }

even though the received string is GOTO MUSIC its printing in the console as please try again.

[VRonin]

https://forum.qt.io/topic/10210/solved-qml-strcmp-in-qml

[jsulm]

@Naveen_D I'm not JavaScript expert (what QML basically is), but as far as I know you can use === instead of ==
If there maybe a new line at the end of receivedString ?

[Naveen_D]

@jsulm @VRonin i just tried with that... i don't know do i need to use javascript for this or wat...i simply tried once with that code...
Is it necessary to javascript to do this...because in Qt i use to do it using == so i thought here it will be the same...

[jsulm]

@Naveen_D QML is JavaScript.
Did you check the link provided by @VRonin ?

[Naveen_D]

@jsulm ya i checked...after checking that code only i used var in the code as shown above...but i didn't get that clearly so posted this in forum.