UI is not responding in QThread

DhivyaJR

Hi I am trying a simple program where I created a sub-class for QObject and emitting a signal from it and trying to capture in a slot and display the value on UI , it enters the slot, but and printing the qdebug () message, but UI is not responding

Here is my code snnippet.
display.h

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QString>
#include "mythread.h"

namespace Ui {
class dialog;
}

class dialog : public QDialog
{
    Q_OBJECT

public:
    explicit dialog(QWidget *parent = 0);
    ~dialog();
    bool stop;
private:
    Ui::dialog *ui;

public slots:
    void onValueChanged(int);

private slots:
    // for Start button
    void on_pushButton_clicked();

    // for Stop button
    void on_pushButton_2_clicked();
};

#endif // DIALOG_H

display.cpp

#include "dialog.h"
#include "ui_dialog.h"
#include "mythread.h"
#include "process.h"
#include "capture.h"
#include <QDebug>

dialog::dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::dialog)
{
    ui->setupUi(this);
}

dialog::~dialog()
{
    delete ui;
}

// Absorb the signal emitted from a run() method
// and reflect the count change to the count label
// in our dialog

void dialog::onValueChanged(int count)
{
    qDebug()<<"On Value changed"<< count;
    ui->label->setText(QString::number(count));
}

// Start button
void dialog::on_pushButton_clicked()
{  
    Capture capture_thread;
    QObject::connect(&capture_thread,&Capture::inputAvailable,
                    this, &dialog::onValueChanged);
    capture_thread.startCapture();
}

// Stop button
void dialog::on_pushButton_2_clicked()
{
    stop = true;
}

capture.h

#ifndef CAPTURE_H
#define CAPTURE_H

#include <QObject>

namespace Ui {
class Capture;
}
class Capture : public QObject
{
    Q_OBJECT
public:
    explicit Capture(QObject *parent = nullptr);
signals:
     void inputAvailable(int i);

public slots:
    void startCapture();

};

#endif // CAPTURE_H

capture.cpp

#include "capture.h"
#include <QMutex>
#include <QThread>
#include "dialog.h"
static int check = 0;
Capture::Capture(QObject *parent) : QObject(parent)
{

}

void Capture::startCapture()
{
    dialog d;
    while(1)
    {
        int i = check;
        QMutex mutex;
        // prevent other threads from changing the "Stop" value
        mutex.lock();
        if (d.stop == true)break;
        mutex.unlock();

        // emit the signal for the count label
        emit inputAvailable(i);

        check++;
        // slowdown the count change, msec
        QThread::msleep(500);
    }

}

When Start button is clicked from UI,I am getting output as follows

10:20:56: Starting /home/dhivyajr/build-qThreadDisplay_learining-Desktop_Qt_5_15_2_GCC_64bit-Debug/qThreadDisplay_learining ...
On Value changed 0
On Value changed 1
On Value changed 2
On Value changed 3
On Value changed 4
On Value changed 5
On Value changed 6
On Value changed 7
On Value changed 8
On Value changed 9

But UI is not responding

jsulm

@DhivyaJR said in UI is not responding in QThread:

void dialog::on_pushButton_clicked()
{
Capture capture_thread;
QObject::connect(&capture_thread,&Capture::inputAvailable,
this, &dialog::onValueChanged);
capture_thread.startCapture();
}

startCapture() is a blocking call, so you are blocking the UI thread.
Also, I don't see where you are using any other threads? Everything is running in UI thread.
Please read https://doc.qt.io/qt-5/thread-basics.html if you want to do multi threading.