QObject::connect: Cannot connect (null) problem in QML binding with C++

xiazhouquan

I implement a class to download a file from http
@
DownLoadFile.h

#ifndef DOWNLOADFILE_H
#define DOWNLOADFILE_H
#include <QObject>
#include <QUrl>
#include <QFile>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>

class CDownLoadFile: public QObject
{
Q_OBJECT
public:
explicit CDownLoadFile(QObject *parent=0);

public slots:
Q_INVOKABLE void downloadFile(QUrl url);
Q_INVOKABLE void httpReadyRead();
Q_INVOKABLE void httpFinished();
private:
QUrl url;
QNetworkAccessManager *pmanager;
QNetworkReply *preply;
QFile *pfile;
};

#endif // DOWNLOADFILE_H
@

@

DownLoadFile.cpp

#include "DownLoadFile.h"
#include <QtGui>
#include <QtNetwork>
#include <QNetworkAccessManager>

CDownLoadFile::CDownLoadFile(QObject *parent)
:QObject(parent)
{

}

void CDownLoadFile::downloadFile(QUrl url)
{
QFileInfo fileInfo(url.path());
QString fileName = fileInfo.fileName();
pfile = new QFile(fileName);
pmanager=new QNetworkAccessManager();
QObject::connect(preply, SIGNAL(readyRead()),this, SLOT(httpReadyRead()));
QObject::connect(preply,SIGNAL(finished()),this,SLOT(httpFinished()));
preply= pmanager->get(QNetworkRequest(url));
}

void CDownLoadFile::httpReadyRead()
{
if (pfile)
pfile->write(preply->readAll());
}

void CDownLoadFile::httpFinished()
{
pfile->flush();

pfile->close();

preply->deleteLater();

preply = 0;

delete pfile;

pfile = 0;

}
@

In the QML file ,I use it link this
@
import CDownLoadFile 1.0
CDownLoadFile{id:epubdownload}
epubdownload.downloadFile("http://s3.amazonaws.com/manybooksepub/munroeki3565235652-8epub.epub")

@

I register CDownLoadFile in the main.cpp link this
@
qmlRegisterType<CDownLoadFile>("CDownLoadFile", 1,0, "CDownLoadFile");

@

But when I run the application,something wrong with this:
QObject::connect: Cannot connect (null)::readyRead() to CDownLoadFile::httpReadyRead()
QObject::connect: Cannot connect (null)::finished() to CDownLoadFile::httpFinished()

I can't find any solution about the problem!

Thank you for your reply!
My regards!

tobias.hunger

You are connecting the object preply points to (most likely preply is 0 at that point) and then have it point to the object you care about.

Try this instead:
@
preply= pmanager->get(QNetworkRequest(url));
QObject::connect(preply, SIGNAL(readyRead()),this, SLOT(httpReadyRead()));
QObject::connect(preply,SIGNAL(finished()),this,SLOT(httpFinished()));
@

xiazhouquan

Thank Tobias Hunger ,I have solved the problem.preply= pmanager->get(QNetworkRequest(url)); is ok