Qt - Simple example using threads controlled by push buttons - c++

Question

I have been trying to get this simple example using threads activated by pushbuttons to work. It is based off of the solution in the question below:
How to implement frequent start/stop of a thread (QThread)
The main differences between the example solution above and my code below are:
I used a QWidget instead of MainWindow
I changed the name of signals for clarity
My code contains debugging information
I experimented with eliminating the signals created by worker as the didn't appear to do anything
It appears that the start/stop signals are not triggering their corresponding slots, but I am not experienced enough to troubleshoot why.
Additionally, I am unsure of the purpose of the signal:
SignalToObj_mainThreadGUI()
Is that just something that could be used and is not?
I have been trying to get this code to work for some time, so any help would be greatly appreciated.
main.cpp
#include "threadtest.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
ThreadTest w;
w.show();
return a.exec();
}
threadtest.h
#include <QWidget>
#include <QThread>
#include "worker.h"
namespace Ui
{
class ThreadTest;
}
class ThreadTest : public QWidget
{
Q_OBJECT
public:
explicit ThreadTest(QWidget *parent = 0);
~ThreadTest();
signals:
void startWorkSignal();
void stopWorkSignal();
private slots:
void on_startButton_clicked();
void on_stopButton_clicked();
private:
Ui::ThreadTest *ui;
worker *myWorker;
QThread *WorkerThread;
};
threadtest.cpp
#include "threadtest.h"
#include "ui_threadtest.h"
ThreadTest::ThreadTest(QWidget *parent) :
QWidget(parent),
ui(new Ui::ThreadTest)
{
ui->setupUi(this);
myWorker = new worker;
WorkerThread = new QThread;
myWorker->moveToThread(WorkerThread);
connect(this,
SIGNAL(startWorkSignal()),
myWorker,
SLOT(StartWork())
);
connect(this,
SIGNAL(stopWorkSignal()),
myWorker,
SLOT(StopWork())
);
//Debug
this->dumpObjectInfo();
myWorker->dumpObjectInfo();
}
ThreadTest::~ThreadTest()
{
delete ui;
}
void ThreadTest::on_startButton_clicked()
{
qDebug() << "startwork signal emmitted";
emit startWorkSignal();
}
void ThreadTest::on_stopButton_clicked()
{
qDebug() << "stopwork signal emmitted";
emit stopWorkSignal();
}
worker.h
#include <QObject>
#include <QDebug>
class worker : public QObject {
Q_OBJECT
public:
explicit worker(QObject *parent = 0);
~worker();
signals:
void SignalToObj_mainThreadGUI();
//void running();
//void stopped();
public slots:
void StopWork();
void StartWork();
private slots:
void do_Work();
private:
volatile bool running, stopped;
};
worker.cpp
#include "worker.h"
worker::worker(QObject *parent) : QObject(parent), stopped(false),
running(false)
{
qDebug() << "running: " << running;
qDebug() << "stopped: " << stopped;
}
worker::~worker() {}
void worker::do_Work()
{
qDebug() << "inside do Work";
emit SignalToObj_mainThreadGUI();
if (!running || stopped) return;
// actual work here
/*
for (int i = 0; i < 100; i++)
{
qDebug() << "count: " + i;
}
*/
QMetaObject::invokeMethod(this, "do_Work", Qt::QueuedConnection);
}
void worker::StopWork()
{
qDebug() << "inside StopWork";
stopped = true;
running = false;
//emit stopped();
}
void worker::StartWork()
{
qDebug() << "inside StartWork";
stopped = false;
running = true;
//emit running();
do_Work();
}

Answer 1

You should write
WorkerThread->start();
Or you can use the thread of the ThreadTest object instead the WorkerThread (in this case the WorkerThread is needless):
myWorker->moveToThread(thread()); // this->thread

Answer 2

The slots are not triggered, because you have moved myWork to the thread WorkerThread, but didnot run an event loop in that thread. In threadtest.cpp, add
WorkerThread .start();
after
myWorker = new worker;
WorkerThread = new QThread;
myWorker->moveToThread(WorkerThread);