necessitas: android intent & QProcess issues

[tpf80]

Currently I am working on a simple application which is meant to spawn the ZXING barcode scanner.

Using QProcess, I am able to make a slot which launches the scanner application and then returns to my application when a scan has completed.

A few problems have occurred which I can not figure out:

1) When launchScanner() is called, the "item scanned!", and "scanner output" messages appear instantly and the stacked widget changes index even though the scanner application is not finished. The scanner window is still open while my app continues under it. This means that my slot is not waiting for the scanner to finish before moving on. I am not sure if this is an issue with QProcess on the android or something I missed in my code.

2) readAll() returns "Starting: Intent { act=com.google.zxing.client.android.SCAN (has extras) }" rather than any return value (barcode contents) from the scanner finishing it's scan. This could be caused by QProcess not waiting thereby leaving readall() to only report the results right after it started rather than everything.

Is there a better way to use an intent than launching it with QProcess? Also, how can I get the return information once I call it?

void MainWindow::launchScanner() {
 
    QProcess barcode;
    barcode.setProcessChannelMode(QProcess::MergedChannels);
 
    barcode.start("am start -a com.google.zxing.client.android.SCAN -e SCAN_FORMATS \"QR_CODE\"");
 
    if (!barcode.waitForStarted()) {
        qDebug() << "********************** Scanner start failed! " << barcode.errorString();
    } else {
        qDebug() << "********************** Scanner started!";
    }
 
 
    if (!barcode.waitForFinished(-1)) {
        qDebug() << "********************** Scanner unable to finish! " << barcode.errorString();
    } else {
        qDebug() << "********************** Scanner output: " << barcode.readAll();
    }
 
    //do something here once we figure out how to get value back from the scanner
 
    qDebug() << "********************** Item scanned! ******************************";
 
 
    //change the stack widget to show a different interface
    ui.mainStack->setCurrentIndex(1);
}

void MainWindow::launchScanner() {

    QProcess barcode;
    barcode.setProcessChannelMode(QProcess::MergedChannels);

    barcode.start("am start -a com.google.zxing.client.android.SCAN -e SCAN_FORMATS \"QR_CODE\"");

    if (!barcode.waitForStarted()) {
        qDebug() << "********************** Scanner start failed! " << barcode.errorString();
    } else {
        qDebug() << "********************** Scanner started!";
    }


    if (!barcode.waitForFinished(-1)) {
        qDebug() << "********************** Scanner unable to finish! " << barcode.errorString();
    } else {
        qDebug() << "********************** Scanner output: " << barcode.readAll();
    }

    //do something here once we figure out how to get value back from the scanner

    qDebug() << "********************** Item scanned! ******************************";


    //change the stack widget to show a different interface
    ui.mainStack->setCurrentIndex(1);
}

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[mvuori]

About making QProcess wait for the process to complete, see an old illustrative discussion http://lists.trolltech.com/qt-intere...ad01232-0.html

[tpf80]

I modified my code to work using signals/slots to go to the next step and the result was the same: the process instantly starts, finishes, and updates the interface behind the running scanner, which did not finish until I scanned a barcode.

I think what could be happening is that QProcess is launching the "am" command, which in turn launches the program. After the program launches, the "am" command exits and so QProcess signals that and is not actually attached to the barcode scanner at all.

This may or may not be a problem as long as I can figure out how I can get at the result intent. Any ideas?

MainWindow::MainWindow(QWidget *parent) {
 
    ui.setupUi(this);
 
    barcode = new QProcess();
 
    connect(barcode, SIGNAL(readyReadStandardOutput()), this, SLOT(readScannerOutput()));
    connect(barcode, SIGNAL(started()), this, SLOT(scannerStarted()));
    connect(barcode, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(scannerFinished(int, QProcess::ExitStatus)));
 
 
    connect( ui.checkinButton, SIGNAL( clicked() ), this, SLOT( launchScanner() ) );
 
 
 
}
 
MainWindow::~MainWindow() {
 
}
 
//slot to launch the scanner and do something with the result:
void MainWindow::launchScanner() {
 
 
    //if the scanner is not already running launch the scanner:
    if (barcode->state() == QProcess::Running) {
 
        qDebug() << "********************** Scanner was already running! Do not start again!";
 
    } else {
 
        barcode->setProcessChannelMode(QProcess::MergedChannels);
        barcode->setReadChannel(QProcess::StandardOutput);
        barcode->start("am start -a com.google.zxing.client.android.SCAN -e SCAN_FORMATS \"QR_CODE\"");
        qDebug() << "********************** Starting scanner...";
 
    }
 
 
}
 
void MainWindow::scannerStarted() {
 
    qDebug() << "********************** Scanner started!";
 
}
 
void MainWindow::scannerFinished(int exitCode, QProcess::ExitStatus exitStatus) {
 
    if (exitStatus == QProcess::CrashExit) {
        qDebug() << "********************** Barcode scanner crashed!" << barcode->errorString();
    } else {
        qDebug() << "********************** Barcode scanner finished!" << barcode->readAll();
        ui.mainStack->setCurrentIndex(1);
        qDebug() << "********************** Interface changed to the next step.";
    }
 
}
 
 
void MainWindow::readScannerOutput() {
 
    QTextStream s(barcode);
    QString str = s.readAll();
    qDebug() << "********************** The scanner speaks: " << str;
 
}

MainWindow::MainWindow(QWidget *parent) {

    ui.setupUi(this);

    barcode = new QProcess();

    connect(barcode, SIGNAL(readyReadStandardOutput()), this, SLOT(readScannerOutput()));
    connect(barcode, SIGNAL(started()), this, SLOT(scannerStarted()));
    connect(barcode, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(scannerFinished(int, QProcess::ExitStatus)));


    connect( ui.checkinButton, SIGNAL( clicked() ), this, SLOT( launchScanner() ) );



}

MainWindow::~MainWindow() {

}

//slot to launch the scanner and do something with the result:
void MainWindow::launchScanner() {


    //if the scanner is not already running launch the scanner:
    if (barcode->state() == QProcess::Running) {

        qDebug() << "********************** Scanner was already running! Do not start again!";

    } else {

        barcode->setProcessChannelMode(QProcess::MergedChannels);
        barcode->setReadChannel(QProcess::StandardOutput);
        barcode->start("am start -a com.google.zxing.client.android.SCAN -e SCAN_FORMATS \"QR_CODE\"");
        qDebug() << "********************** Starting scanner...";

    }


}

void MainWindow::scannerStarted() {

    qDebug() << "********************** Scanner started!";

}

void MainWindow::scannerFinished(int exitCode, QProcess::ExitStatus exitStatus) {

    if (exitStatus == QProcess::CrashExit) {
        qDebug() << "********************** Barcode scanner crashed!" << barcode->errorString();
    } else {
        qDebug() << "********************** Barcode scanner finished!" << barcode->readAll();
        ui.mainStack->setCurrentIndex(1);
        qDebug() << "********************** Interface changed to the next step.";
    }

}


void MainWindow::readScannerOutput() {

    QTextStream s(barcode);
    QString str = s.readAll();
    qDebug() << "********************** The scanner speaks: " << str;

}

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[jacekkozik]

hi buddy, I have the same problem. Do you know how to read the result intent? Please reply as you solved this problem.