QT Linux - QObject::connect & QHttp issue - qt

Question

I have a problem. I'm writing a small application, which will fetch an image from a website and display it in a QT GUI application.
I use QHttp to do this. The code works if I execute it in main (before GUI is shown), but when I try to implement it, so that the code will run when I click on a button, it doesn't work.
Here's some of the code:
downloader.h - The class that's responsible for creating connection and saving image
#ifndef DOWNLOADER_H
#define DOWNLOADER_H
#include <QObject>
#include <QHttp>
#include <QFile>
#include <QDebug>
#include <QDir>
class Downloader : public QObject
{
Q_OBJECT
public:
explicit Downloader(QObject *parent = 0);
void getImageFromWeb(QString host, QString append);
signals:
public slots:
void stateChanged(int state);
void responseHeaderReceived(const QHttpResponseHeader &resp);
void requestFinished(int id, bool error);
private:
QHttp *http;
};
#endif // DOWNLOADER_H
downloader.cpp - The implementation
The case switches are added for debugging
#include "downloader.h"
#include <QApplication>
Downloader::Downloader(QObject *parent) :
QObject(parent)
{
}
void Downloader::getImageFromWeb(QString host, QString append)
{
http = new QHttp(this);
connect(http, SIGNAL(stateChanged(int)), this, SLOT(stateChanged(int)));
qDebug() << "Connect 1";
connect(http, SIGNAL(responseHeaderReceived(QHttpResponseHeader)), this, SLOT(responseHeaderReceived(QHttpResponseHeader)));
qDebug() << "Connect 2";
connect(http, SIGNAL(requestFinished(int,bool)), this, SLOT(requestFinished(int,bool)));
qDebug() << "Connect 3";
http->setHost(host);
http->get(append);
}
void Downloader::stateChanged(int state)
{
switch(state)
{
case 0:
qDebug() << "Unconnected";
break;
case 1:
qDebug() << "Hhost Lookup";
break;
case 2:
qDebug() << "Connection";
break;
case 3:
qDebug() << "Sending";
break;
case 4:
qDebug() << "Reading";
break;
case 5:
qDebug() << "Connect";
break;
case 6:
qDebug() << "Closing";
break;
}
}
void Downloader::responseHeaderReceived(const QHttpResponseHeader &resp)
{
qDebug() << "Size" << resp.contentLength();
qDebug() << "Type" << resp.contentType();
qDebug() << "Status" << resp.statusCode();
}
void Downloader::requestFinished(int id, bool error)
{
if(error)
{
qDebug() << "ERROR!";
}
else
{
qDebug() << "OK";
QFile *file = new QFile(QDir::currentPath() + "/image.png");
if(file->open(QFile::Append))
{
file->write(http->readAll());
file->flush();
file->close();
}
delete file;
}
}
main.cpp - The code above works correctly if it is implemented like this
#include "mainwindow.h"
#include <QApplication>
#include <downloader.h>
int main(int argc, char *argv[])
{
Downloader getImage;
getImage.getImageFromWeb("servlet.dmi.dk", "/byvejr/servlet/byvejr?by=8000&tabel=dag3_9");
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
Instead of this, I would like the image to be fetched when I press a button in the program, so I tried this:
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "downloader.h"
#include <QApplication>
#include <QDir>
void MainWindow::on_pushButton_clicked()
{
Downloader getImage;
getImage.getImageFromWeb("www.dmi.dk/", "/uploads/tx_dmidatastore/webservice/k/d/_/n/g/femdgn_dk.png");
}
This doesn't work. From the debugger I get:
Connect 1
Connect 2
Connect 3
When it works (when it's implemented in main.cpp) the debugger gives me something like:
Connect 1
Connect 2
Connect 3
OK
Connection
Sending
Reading
Size 16282
Type "image/png"
Status 200
Connect
OK
So I guess this tells me that the connections are made, but nothing is being executed.
Any answer/suggestion is appreciated.
Thanks in advance!

Answer 1

Looks like your getImage object is being descoped/destructed before it can do anything. Try creating a Downloader object as a member of MainWindow instead of inside the on_pushButton_clicked() function.