Question

So I have implemented a thread class in my program that I’m trying to run from my mainwindow, but it is not being recognized. I will post below the thread header and file, as well as the main window header and file.

CONTEXT: The thread contains a loop that goes through the files in a directory and sends a signal to print the title to the mainwindow.

directoryprinter.h (Thread header)

#ifndef DIRECTORYPRINTER_H
#define DIRECTORYPRINTER_H

#include <QThread>
#include <QtCore/QDir>
#include <QtCore/QDirIterator>

class DirectoryPrinter : public QThread
{
    Q_OBJECT
public:
    explicit DirectoryPrinter(QObject *parent = 0);
    void DirectoryParser();
    void run();

signals:
    void SendSignal(QString);

private:
    QDirIterator * it;    
};

#endif // DIRECTORYPRINTER_H

Thread class definitions

#include "directoryprinter.h"

DirectoryPrinter::DirectoryPrinter(QObject *parent) :
    QThread(parent)
{
    it = new QDirIterator ("C:Users/Andrew/",QDirIterator::Subdirectories);
}

void DirectoryPrinter::DirectoryParser()
{
    while (it->hasNext())
    {
        QString String = it->next();
        SendSignal(String);
    }
}

void DirectoryPrinter::run()
{
    this->DirectoryParser();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDebug>
#include <iostream>
#include "directoryprinter.h"

//UNINITIALIZED POINTERS??

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    void Print(QString String);
    ~MainWindow();

private slots:
    void on_pushButton_released();

private:
    Ui::MainWindow *ui;
    DirectoryPrinter *Name; //THIS LINE IS NOT RECOGNIZED
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(Name,SIGNAL(SendSignal(QString)),this,SLOT(Print(QString)));
    }

void MainWindow::Print(QString String)
{
    ui->textBrowser->setText(String);
}

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

void MainWindow::on_pushButton_released()
{
    Name = new DirectoryPrinter();
    Name->start();
}

The program exits with: exited with code -1073741819

However, I believe the issue is with the line I commented above. I am unsure where to begin debugging this, I have a few ideas, but they’d mostly be guesses, and I do not have much experience using threads.

Thanks in advance. et me know if there is any further information required.

Answer 1

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(Name,SIGNAL(SendSignal(QString)),this,SLOT(Print(QString)));
}

In MainWindow‘s constructor, you’re connecting a signal from an object that hasn’t been initialized (you don’t initialize Name until on_pushButton_released() is called). To fix this, create Name in the constructor:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    Name = new DirectoryPrinter(this);//this is the parent; takes care of cleanup
    connect(Name,SIGNAL(SendSignal(QString)),this,SLOT(Print(QString)));
}

void MainWindow::on_pushButton_released()
{
    //Name = new DirectoryPrinter(); not needed here anymore
    Name->start();
}

From the comment below, there is another problem here – namely, MainWindow::Print is not defined as a slot (using the slots: macro). It should be:

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
    //void Print(QString String); // <-- not here...
    ~MainWindow();

public slots:
    void Print(QString String); // <-- here instead

// ...other class-definition stuff
};