Qt -获取源(HTML代码)的网页托管在互联网上

Question

我想获得一个网页的源(HTML)，例如StackOverflow的主页。

这是我目前编写的代码:

QNetworkAccessManager manager;
QNetworkReply *response = manager.get(QNetworkRequest(QUrl(url)));
QString html = response->readAll(); // Source should be stored here

但是什么也没发生!当我试图获得html字符串的值时，它是空的(")。

那么，该怎么办呢?我使用Qt 5.3.1.

Answer 1

您需要以异步方式对其进行编码。c++ 11和Qt来拯救我们。请记住，lambda函数体稍后将在事件循环中执行。

// https://github.com/KubaO/stackoverflown/tree/master/questions/html-get-24965972
#include <QtNetwork>
#include <functional>
void htmlGet(const QUrl &url, const std::function<void(const QString&)> &fun) {
   QScopedPointer<QNetworkAccessManager> manager(new QNetworkAccessManager);
   QNetworkReply *response = manager->get(QNetworkRequest(QUrl(url)));
   QObject::connect(response, &QNetworkReply::finished, [response, fun]{
      response->deleteLater();
      response->manager()->deleteLater();
      if (response->error() != QNetworkReply::NoError) return;
      auto const contentType =
            response->header(QNetworkRequest::ContentTypeHeader).toString();
      static QRegularExpression re("charset=([!-~]+)");
      auto const match = re.match(contentType);
      if (!match.hasMatch() || 0 != match.captured(1).compare("utf-8", Qt::CaseInsensitive)) {
         qWarning() << "Content charsets other than utf-8 are not implemented yet:" << contentType;
         return;
      }
      auto const html = QString::fromUtf8(response->readAll());
      fun(html); // do something with the data
   }) && manager.take();
}
int main(int argc, char *argv[])
{
   QCoreApplication app(argc, argv);
   htmlGet({"http://www.google.com"}, [](const QString &body){ qDebug() << body; qApp->quit(); });
   return app.exec();
}

除非你只使用这段代码一次，你应该把QNetworkManager实例作为你的控制器类的成员，或者在main，等等

Answer 2

你必须添加QEventLoop

QNetworkAccessManager manager;
QNetworkReply *response = manager.get(QNetworkRequest(QUrl(url)));
QEventLoop event;
connect(response,SIGNAL(finished()),&event,SLOT(quit()));
event.exec();
QString html = response->readAll(); // Source should be stored here

Answer 3

QNetworkAccessManager异步工作。您在get()之后立即调用readAll()，但此时还没有发出请求。您需要使用文档中所示的QNetworkAccessManager::finished信号，并将readAll()移动到与该信号连接的槽位

Answer 4

一个简短的回答，包括c++ 17的基本部分:

const auto manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished,
        this, [](auto reply) {
            qDebug() << reply->readAll();
        });
manager->get(QNetworkRequest({ "https://www.google.com" }));