Multi-thread not working in QT - c++

Question

I'm developing C++ application in QT with GUI. To make the GUI always respond, I create a thread for other blocking process. However, the application is waiting for the blocking process and therefore the GUI didn't respond.
Is creating a thread for blocking process is a wrong way?
Or it doesn't work in QT? If so, how to make the GUI respond? Please give me example.

Answer 1

This is a simple example of multithreaded application with responsive GUI:
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPushButton>
#include <QLineEdit>
#include <QThread>
class Worker : public QThread
{
protected:
/// Wait 3s which simulates time demanding job.
void run() { sleep(3); }
};
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
public slots:
void doJob(bool);
void jobFinished();
private:
Worker worker;
QLineEdit *line;
QPushButton *button;
int counter;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include <QVBoxLayout>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent),
line(new QLineEdit()),
button(new QPushButton()),
counter(0)
{
line->setDisabled(true);
line->setAlignment(Qt::AlignRight);
line->setText(QString::number(counter));
button->setText("Push");
connect(button, SIGNAL(clicked(bool)), this, SLOT(doJob(bool)));
connect(&worker, SIGNAL(finished()), this, SLOT(jobFinished()));
QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(line);
layout->addWidget(button);
QWidget *window = new QWidget();
window->setLayout(layout);
setCentralWidget(window);
}
void MainWindow::doJob(bool)
{
// Only one thread is running at a time.
// If you want a thread pool, the implementation is up to you :)
worker.start();
// Uncomment to wait. If waiting, GUI is not responsive.
//worker.wait();
}
void MainWindow::jobFinished()
{
++counter;
line->setText(QString::number(counter));
}
Qt has a very good multithreading support. You probably do something wrong and we can't help you if you don't provide any code. There are a lot of ways of implementing "responsive" GUI! (Including a lot of ways how to implement another thread!)