c++ - 当尝试使用 Qt QNetworkAccessManager 获取网页时，它总是返回 ""

Question

我正在尝试使用 Qt 获取网页并将其打印在屏幕上。问题是它总是打印“”。它不会进入完成的 SLOT。不知道是不是connect()有问题。代码编译没有错误。 尝试不使用事件循环。

代码如下:

网络.h

#ifndef NET_H
#define NET_H

#include <QObject>
#include <QtNetwork>
#include <QString>
#include <QDebug>

class net : public QObject
{
    Q_OBJECT
public:
    explicit net(QObject *parent = 0);
    void get_site(QString url);
    QString data;

signals:

public slots:
    void err(QNetworkReply *);
    void done(QNetworkReply *);

private:

};

#endif // NET_H

net.cpp:

#include "net.h"

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

void net::get_site(QString url) {
    QNetworkAccessManager man;
    QNetworkRequest request;

    request.setUrl (QUrl(url));

    connect (&man , SIGNAL(finished(QNetworkReply*)) ,this, SLOT(done(QNetworkReply*)));
    connect (&man , SIGNAL(finished(QNetworkReply*)) ,this, SLOT(err(QNetworkReply *)));

    man.get (QNetworkRequest(QUrl(url)));
}

void net::done(QNetworkReply * reply) {
    data = QString(reply->readAll ());
}

void net::err(QNetworkReply * reply) {
    data = QString(reply->errorString ());
}

和main.cpp:

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


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

    net netobj;
    netobj.get_site("http://stackoverflow.com");
    qDebug() << netobj.data;
    return a.exec();
}

Answer 1

您的代码中存在一些重大问题。首先，您应该将 QNetworkAccessManager 作为 .h 文件中的类成员:

class net : public QObject
{
    ...
private:
    QNetworkAccessManager nam;
};

此外，您不应将 finished 信号连接到两个不同的插槽。您的 get_site 函数应该是这样的:

void net::get_site(QString url) {

    QNetworkRequest request;
    request.setUrl (QUrl(url));

    connect (&man , SIGNAL(finished(QNetworkReply*)) ,this, SLOT(done(QNetworkReply*)));

    man.get (QNetworkRequest(QUrl(url)));
}

您应该按以下方式管理返回的回复:

void net::done(QNetworkReply * reply) {


    if (reply->error() == QNetworkReply::NoError)
    {
       data = QString(reply->readAll ());
    }
    else
    {
       data = QString(reply->errorString ());
    }
}