qthread QNetworkAccessManager QEventLoop

qthread QNetworkAccessManager QEventLoop

进程通过QNetworkAccessManager 进行http请求。代码如下：

// qhttp.h
#ifndef QHTTP_H
#define  QHTTP_H

#include  < QtGui / QWidget >
#include  " ui_qhttp.h "
#include  < QNetworkAccessManager >
#include  < QUrl >

class  QPushButton;
class  QDialogButtonBox;
class  QNetworkReply;

class  qhttp :  public  QWidget
{
    Q_OBJECT

public:
    qhttp(QWidget *parent = 0);
    ~qhttp();

    void startRequest(QUrl url);

private:
    Ui::qhttpClass ui;

    QPushButton *downloadButton;
    QDialogButtonBox *buttonBox;

    QUrl url;
    QNetworkAccessManager qnam;
    QNetworkReply *reply;

private slots:
    void downloadFile();
    void httpFinished();
} ;

#endif   //  QHTTP_H


// qhppt.cpp
#include  " qhttp.h "
#include  < QtGui >
#include  < QtNetwork >
#include  < iostream >

using   namespace  std;

qhttp::qhttp(QWidget  * parent)
    : QWidget(parent)
{
    ui.setupUi(this);

    downloadButton = new QPushButton(tr("Download"));
    downloadButton->setDefault(true);


    buttonBox = new QDialogButtonBox;
    buttonBox->addButton(downloadButton, QDialogButtonBox::ActionRole);

    connect(downloadButton, SIGNAL(clicked()), this, SLOT(downloadFile()));

    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addWidget(buttonBox);
    setLayout(mainLayout);
}

qhttp:: ~ qhttp()
{

}

void  qhttp::downloadFile()
{
    cout<<"downloadFile"<<endl;
    url = "http://www.baidu.com/";
    startRequest(url);
}

void  qhttp::startRequest(QUrl url)
{
    cout<<"startRequest"<<endl;
    reply = qnam.get(QNetworkRequest(url));
     connect(reply, SIGNAL(finished()), this, SLOT(httpFinished()));
}

void  qhttp::httpFinished()
{
    cout<<"httpFinished"<<endl;
    if(reply->error())
    {
        cout<<"error:"<<qPrintable(reply->errorString())<<endl;
    }
    else
    {
        cout<<"right"<<endl;
    }
}

但当主进程开辟线程来执行http请求时，却无法成功。

//qhttp.h
#ifndef QHTTP_H
#define QHTTP_H

#include <QtGui/QWidget>
#include "ui_qhttp.h"
#include <QNetworkAccessManager>
#include <QUrl>

class QPushButton;
class QDialogButtonBox;
class QNetworkReply;
class qhttpThread;

class qhttp : public QWidget
{
    Q_OBJECT

public:
    qhttp(QWidget *parent = 0);
    ~qhttp();

    void startRequest(QUrl url);

private:
    Ui::qhttpClass ui;

    QPushButton *downloadButton;
    QDialogButtonBox *buttonBox;

    QUrl url;
    QNetworkAccessManager qnam;
    QNetworkReply *reply;
     qhttpThread *httpthread;

private slots:
    void downloadFile();
    void httpFinished();
};

#endif // QHTTP_H



//qhttp.cpp
#include "qhttp.h"
#include "qhttpThread.h"
#include <QtGui>
#include <QtNetwork>
#include <iostream>

using namespace std;

qhttp::qhttp(QWidget *parent)
    : QWidget(parent)
{
    ui.setupUi(this);

    downloadButton = new QPushButton(tr("Download"));
    downloadButton->setDefault(true);


    buttonBox = new QDialogButtonBox;
    buttonBox->addButton(downloadButton, QDialogButtonBox::ActionRole);

    connect(downloadButton, SIGNAL(clicked()), this, SLOT(downloadFile()));

    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addWidget(buttonBox);
    setLayout(mainLayout);
}

qhttp::~qhttp()
{

}

void qhttp::downloadFile()
{
    cout<<"downloadFile"<<endl;
    //url = "http://www.baidu.com/";
    //startRequest(url);

    httpthread = new qhttpThread(this);
    httpthread->start();
}

void qhttp::startRequest(QUrl url)
{
    cout<<"startRequest"<<endl;
    reply = qnam.get(QNetworkRequest(url));
    connect(reply, SIGNAL(finished()), this, SLOT(httpFinished()));
}

void qhttp::httpFinished()
{
    cout<<"httpFinished"<<endl;
    if(reply->error())
     {
        cout<<"error:"<<qPrintable(reply->errorString())<<endl;
    }
    else
     {
        cout<<"right"<<endl;
    }
}

此时会出现程序运行崩溃、没有执行http请求任务等情况。
简单说一下注意事项：
1  线程中的run函数返回后线程即结束，根本无法等到reply的finished信号。因此需要加入QEventLoop来挂起线程。

2  通过connect设置信号槽，需要QObject的支持，因此在构造函数里与头文件中需要修改代码。
最终的修改代码如下：

//qhttpThread.h
#ifndef QHTTPTHREAD_H_
#define QHTTPTHREAD_H_

#include <QThread>
#include <QObject>
#include <QNetworkAccessManager>
#include <QUrl>

class QNetworkReply;
class QEventLoop;

class qhttpThread : public QThread  {
    Q_OBJECT
public:
    qhttpThread(QObject *parent = 0);
    virtual ~qhttpThread();

    void run();

private:
    QUrl url;
    QNetworkAccessManager qnam;
    QNetworkReply *reply;
    QEventLoop *loop;

    void startRequest(QUrl url);

private slots:
    void httpFinished();
};

#endif /* QHTTPTHREAD_H_ */




//qhttpThread.cpp
#include "qhttpThread.h"
#include <QtNetwork>
#include <QEventLoop>
#include <iostream>
using namespace std;

qhttpThread::qhttpThread (QObject *parent) : QThread(parent)  {
    // TODO Auto-generated constructor stub

}

qhttpThread::~qhttpThread()  {
    // TODO Auto-generated destructor stub
}

void qhttpThread::run()
{
    cout<<"run"<<endl;
    url = "http://www.baidu.com/";
    startRequest(url);


     exec();
    cout<<"run end"<<endl;
}

void qhttpThread::startRequest(QUrl url)
{
    cout<<"startRequest"<<endl;

     loop = new QEventLoop;
    reply = qnam.get(QNetworkRequest(url));
    connect(reply, SIGNAL(finished()), this, SLOT(httpFinished()));

     loop->exec();
    cout<<"startRequest end"<<endl;
}

void qhttpThread::httpFinished()
{
    cout<<"httpFinished"<<endl;
    if(reply->error())
     {
        cout<<"error:"<<qPrintable(reply->errorString())<<endl;
    }
    else
     {
        cout<<"right"<<endl;
    }
     loop->quit();
}

这样，就可以对http进行请求了。

但在真正的执行中，当关闭界面程序时出现弹出框，提示：This application has requested the Runtime to terninate it in an unusual way.
原因还在查找中。