QNetworkAccessManager 失败

Question

我正在关注此文档 http://developer.nokia.com/community/wiki/Creating_an_HTTP_network_request_in_Qt 尝试实现 http 连接，并且我的代码编译没有错误，但是当程序启动时，它崩溃了。

//coreeng.cpp

#include "coreeng.h"
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QImageReader>

coreEng::coreEng(QObject *parent) :
    QObject(parent)
{
}

void coreEng::connect(){
    QObject::connect(nam, SIGNAL(finished(QNetworkReply*)),
    this, SLOT(finishedSlot(QNetworkReply*)));
}

void coreEng::url(){
    QUrl url("http://www.forum.nokia.wiki");
    QNetworkReply* reply = nam->get(QNetworkRequest(url));
}

void coreEng::finishedSlot(QNetworkReply* reply){

    QVariant statusCodeV = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);

    QVariant redirectionTargetUrl = reply->attribute(QNetworkRequest::RedirectionTargetAttribute);

    if (reply->error() == QNetworkReply::NoError)
    {

        QImageReader imageReader(reply);
        QImage pic = imageReader.read();

        QByteArray bytes = reply->readAll();  // bytes
        QString string(bytes); // string
    }

    else
    {

    }

    delete reply;

}

//coreeng.h

#ifndef COREENG_H
#define COREENG_H

#include <QObject>
#include <QNetworkAccessManager>

class coreEng : public QObject
{
    Q_OBJECT
        public:
            explicit coreEng(QObject *parent = 0);
        private slots:

        public slots:
            void connect();
            void url();
            void finishedSlot(QNetworkReply* reply);


        private:
            QNetworkAccessManager* nam;

};

#endif // COREENG_H

//main.cpp

#include <QCoreApplication>
#include "coreeng.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    coreEng mConnect;
    mConnect.connect();

    return a.exec();
}

Answer 1

你应该多注意你的c++代码：

QNetworkAccessManager* nam;

nam 已使用但从未创建。你应该在coreEng构造函数中创建它：

coreEng::coreEng(QObject *parent) :
    QObject(parent), nam( new QNetworkAccessManager(this) )
{
}

另一个问题是：

delete reply;

Qt docs 说：

不要删除连接到这个信号的槽中的回复对象。使用 deleteLater()。