发送信号时，Qt C++插槽不被调用

调试后，我确信当我调用这个->getNetReply（）时没有调用replyFinish（）槽。这些是我的文件，在main（）函数中，我这样调用getNetReply：Networking a；a.getNetReply（）；我确实在qmake中添加了QT+=网络。请帮帮我。非常感谢。

我的networking.cpp文件

#include "networking.h"
#include <QUrl>
#include <QNetworkRequest>
// constructor    
void Networking::getNetReply(){
    QNetworkAccessManager *man  = new QNetworkAccessManager(this);
    QObject::connect(man, SIGNAL(finished(QNetworkReply *)), this, SLOT(replyFinished(QNetworkReply *)));
    qDebug() << "connected";
    QNetworkRequest req;
    req.setUrl(QUrl("http://www.google.com"));
    man->get(req);
}
// this method not called
void Networking::replyFinished(QNetworkReply *reply){
    QByteArray data = reply->readAll();
    QString str = QString(data);
    this->netRep = str;
    code = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
}

我的networking.h头文件：

#ifndef NETWORKING_H
#define NETWORKING_H
#include <QObject>
#include <QNetworkAccessManager>
#include <QNetworkReply>
class Networking : public QObject
{
    Q_OBJECT
public:
    QString netRep;
    int code;
    explicit Networking(QObject *parent = 0);
    void getNetReply();
public slots:
    void replyFinished(QNetworkReply*);
};
#endif // NETWORKING_H