QThread Background?



  • Hey there all is there a way I can have a QThread run in the background and still allow the users to continue doing whatever they want? Or even have the that thread continue ti run, until it's done while the main application exits? Currently I have my main app taking a picture and then a I have a class that I run as a thread, however the user still can't do anything until the thread I launched finishes.

    Any insight would be helpful.



  • Read "this":http://doc.qt.nokia.com/qq/qq27-responsive-guis.html to keep the GUI responsive.
    The thread you run is a child of the main app thread, so when you close it, also the thread will stop. What I could suggest you is make another application called inside the main app.

    hope this help



  • Threads can do you all you need. I guess you are using them in the wrong way, but there is no way to be sure without seeing the (relevant) code.



  • [quote author="Andre" date="1321254162"]Threads can do you all you need. I guess you are using them in the wrong way, but there is no way to be sure without seeing the (relevant) code. [/quote]

    Here is what I'm currently doing

    capture class headers
    @
    #ifndef CAPIT_H
    #define CAPIT_H

    #include <QMainWindow>
    #include <Qt>
    #include <QtCore>
    #include <QtGui>
    #include <QtGlobal>

    #include "upload.h"

    namespace Ui {
    class CapIt;
    }

    class CapIt : public QMainWindow
    {
    Q_OBJECT

    public:
    QByteArray m_imagedata;
    QPixmap m_screenshot;
    QPoint origin, dest;

    /**
     * Constructor & Destructor
     */
    explicit CapIt(QWidget *parent = 0);
    ~PixlDrop();
    
    /**
     * Functions
     */
    QPixmap shootScreen();
    void screenshotWriteout();
    
    /**
     * Events
     */
    void mouseReleaseEvent(QMouseEvent *event);
    

    private:
    Ui::CapIt *ui;
    upload *upld;

    };

    #endif
    @

    capture class
    @
    void CapIt::mouseReleaseEvent(QMouseEvent *event)
    {
    if (event->button() == Qt::LeftButton)
    {
    dest = event->pos();
    delete selected;
    m_screenshot = shootScreen();
    screenshotWriteout();

        // here is where I call my upload class that that has the QThread subclass and my own
        // run implementation
        upld->run(m_imagedata);
    }
    
    // at this point I would like this part of the app to close as it no longer needed and
    // just keep the upld thread running until the upload has finished.
    

    }@

    upload h
    @
    #ifndef UPLOAD_H
    #define UPLOAD_H

    #include <QMainWindow>
    #include <Qt>
    #include <QtCore>
    #include <QtGui>
    #include <QtGlobal>
    #include <QThread>
    #include <QNetworkAccessManager>
    #include <QNetworkRequest>
    #include <QNetworkReply>

    class upload : public QThread
    {
    Q_OBJECT
    public:
    QByteArray m_uploaddata;

    explicit upload(QObject *parent = 0);
    bool imageUpload();
    void loadImage(QString reply_data);
    QString randomString(int len);
    
    virtual void run(QByteArray imagedata);
    

    private slots:
    void finished_upload();

    private:
    QNetworkAccessManager *net;
    QNetworkReply *reply;

    protected:

    };

    #endif
    @

    upload class
    @
    void upload::run(QByteArray imagedata)
    {
    m_uploaddata = imagedata;
    imageUpload();
    }

    bool upload::imageUpload()
    {
    net = new QNetworkAccessManager(this);

    // setup random image name;
    QString file = randomString(15) + ".png";
    
    QNetworkRequest httpReq;
    httpReq.setUrl(QUrl("http://url.to/upload/"));
    
    QString bound("---------------------------723690991551375881941828858");
    QByteArray data(QString("--"+bound+"\r\n").toAscii());
    data += "Content-Disposition: form-data; name=\"action\"\r\n\r\n";
    data += "\r\n";
    data += QString("--" + bound + "\r\n").toAscii();
    
    data += "Content-Disposition: form-data; name=\"file\"; filename=\"" + file +"\"\r\n";
    data += "Content-Type: image/png\r\n\r\n";
    data += m_uploaddata;
    
    data += "\r\n";
    data += QString("--" + bound + "\r\n").toAscii();
    
    httpReq.setRawHeader(QString("Accept-Encoding").toAscii(), QString("gzip,deflate").toAscii());
    httpReq.setRawHeader(QString("Content-Type").toAscii(),QString("multipart/form-data; boundary=" + bound).toAscii());
    httpReq.setRawHeader(QString("Content-Length").toAscii(), QString::number(data.length()).toAscii());
    
    this->reply = net->post(httpReq, data);
    connect(this->reply, SIGNAL(finished()), this, SLOT(finished_upload()));
    
    return true;
    

    }

    void upload::finished_upload()
    {
    if (this->reply->error() == QNetworkReply::NoError)
    loadImage(QString(reply->readAll()));
    else
    QMessageBox::warning(0, "Error", "Unable to upload image.");

    }

    void upload::loadImage(QString reply_data)
    {
    QStringList parts = reply_data.split(";", QString::SkipEmptyParts);

    if (QDesktopServices::openUrl( QUrl(parts[1]) ))
        QApplication::quit();
    

    }
    @



  • Could you please also add the relevant headers?



  • [quote author="Andre" date="1321303094"]Could you please also add the relevant headers?[/quote]

    Added to post.



  • You are calling your reimplemented run method directly. That is not how to use QThread. QThread::run is protected. That means, that it is not meant for outside callers. It is meant to be called by start(), once the new thread has actually started. Remember that QThread only manages a thread, it isn't a thread in itself. What's more, you have created an overloaded version of run, one that takes a QByteArray. That method you just call from your GUI thread, and that causes your run method (and everything else it calls in turn) to also be executed in the GUI thread.

    So, you are not really starting the thread anywhere, and the way you reimplemented the run() method is not going to work.



  • [quote author="Andre" date="1321305664"]You are calling your reimplemented run method directly. That is not how to use QThread. QThread::run is protected. That means, that it is not meant for outside callers. It is meant to be called by start(), once the new thread has actually started. Remember that QThread only manages a thread, it isn't a thread in itself. What's more, you have created an overloaded version of run, one that takes a QByteArray. That method you just call from your GUI thread, and that causes your run method (and everything else it calls in turn) to also be executed in the GUI thread.

    So, you are not really starting the thread anywhere, and the way you reimplemented the run() method is not going to work. [/quote]

    ok how about this

    capit .h
    @
    #ifndef CAPIT_H
    #define CAPIT_H

    #include <QMainWindow>
    #include <Qt>
    #include <QtCore>
    #include <QtGui>
    #include <QtGlobal>

    #include "upload.h"

    namespace Ui {
    class CapIt;
    }

    class CapIt : public QMainWindow
    {
    Q_OBJECT

    public:
    QByteArray m_imagedata;
    QPixmap m_screenshot;
    QPoint origin, dest;

    /**
     * Constructor & Destructor
     */
    explicit CapIt(QWidget *parent = 0);
    ~PixlDrop();
    
    /**
     * Functions
     */
    QPixmap shootScreen();
    void screenshotWriteout();
    
    /**
     * Events
     */
    void mouseReleaseEvent(QMouseEvent *event);
    

    private:
    Ui::CapIt *ui;
    upload *upld;

    };

    #endif
    @

    capit .cpp
    @
    void CapIt::mouseReleaseEvent(QMouseEvent *event)
    {
    if (event->button() == Qt::LeftButton)
    {
    dest = event->pos();
    delete selected;
    m_screenshot = shootScreen();
    screenshotWriteout();

        // spawn new upload thread
        upload upld(m_imagedata);
        upld.start();
    }
    

    @

    upload .h
    @
    #ifndef UPLOAD_H
    #define UPLOAD_H

    #include <QMainWindow>
    #include <Qt>
    #include <QtCore>
    #include <QtGui>
    #include <QtGlobal>
    #include <QThread>
    #include <QNetworkAccessManager>
    #include <QNetworkRequest>
    #include <QNetworkReply>

    class upload : public QThread
    {
    Q_OBJECT

    public:
    QByteArray m_uploaddata;

    // constructor
    upload(QByteArray r_imagedata, QObject *parent = 0);
    
    bool imageUpload();
    void loadImage(QString reply_data);
    QString randomString(int len);
    

    private slots:
    void finished_upload();

    private:
    QNetworkAccessManager *net;
    QNetworkReply *reply;

    protected:
    virtual void run();

    };

    #endif
    @

    upload .cpp
    @
    #include "upload.h"

    upload::upload(QByteArray r_imagedata, QObject *parent) : QThread(parent)
    {
    m_uploaddata = r_imagedata;
    }

    void upload::run()
    {
    imageUpload();
    exec();
    }

    bool upload::imageUpload()
    {
    net = new QNetworkAccessManager(this);

    // setup random image name;
    QString file = randomString(15) + ".png";
    
    QNetworkRequest httpReq;
    httpReq.setUrl(QUrl("http://path.to/upload/"));
    
    QString bound("---------------------------723690991551375881941828858");
    QByteArray data(QString("--"+bound+"\r\n").toAscii());
    data += "Content-Disposition: form-data; name=\"action\"\r\n\r\n";
    data += "\r\n";
    data += QString("--" + bound + "\r\n").toAscii();
    
    data += "Content-Disposition: form-data; name=\"file\"; filename=\"" + file +"\"\r\n";
    data += "Content-Type: image/png\r\n\r\n";
    data += m_uploaddata;
    
    data += "\r\n";
    data += QString("--" + bound + "\r\n").toAscii();
    
    httpReq.setRawHeader(QString("Accept-Encoding").toAscii(), QString("gzip,deflate").toAscii());
    httpReq.setRawHeader(QString("Content-Type").toAscii(),QString("multipart/form-data; boundary=" + bound).toAscii());
    httpReq.setRawHeader(QString("Content-Length").toAscii(), QString::number(data.length()).toAscii());
    
    this->reply = net->post(httpReq, data);
    connect(this->reply, SIGNAL(finished()), this, SLOT(finished_upload()));
    
    return true;
    

    }

    void upload::finished_upload()
    {
    if (this->reply->error() == QNetworkReply::NoError)
    loadImage(QString(reply->readAll()));
    else
    QMessageBox::warning(0, "Error", "Unable to upload image.");

    }

    void upload::loadImage(QString reply_data)
    {
    QStringList parts = reply_data.split(";", QString::SkipEmptyParts);

    if (QDesktopServices::openUrl( QUrl(parts[1]) ))
        QApplication::quit();
    

    }
    @

    However this results in: QThread: Destroyed while thread is still running



  • bq. @// spawn new upload thread
    upload upld(m_imagedata);
    upld.start();@

    The object - upld will be destroyed while you going out of "if(event->button() == Qt::LeftButton)". You should create upld on the heap, not on the stack:
    @upload *upld = new upload(m_imagedata);
    upld->start();@


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