Reading an online file

jocala

I'm trying to implement a simple version checker below. I'm getting a zero error code reading the file, but the file contents show up blank. You can access the file via browser, permissions are ok.

@
void check_version()
{
QNetworkAccessManager *nam = new QNetworkAccessManager();
QUrl data_url("http://www.example.com/version.txt");
QNetworkRequest req(data_url);
QNetworkReply *reply = nam->get(req);
QString data = reply->readAll() ;
QString newver(data);
int err = reply->error();
QString s = QString::number(err);
QMessageBox::critical(0, "",newver+" "+s,QMessageBox::Cancel);
}
@

andreyc

Reply is not immediately available after GET.
Take a look on "Network Download Example":http://qt-project.org/doc/qt-5/qtnetwork-download-example.html

jocala

Thanks. That's a lot of code.

I gather the problem is that I need to wait to read until the get is finished, so I need a signal and a slot: the signal tells the slot to read the data.

@
QObject::connect(&rep, SIGNAL( rep is finished ),
QByteArray newver , SLOT( reply->readAll() ));
@

I know the pseudocode above is bogus, thanks for helping me understand.

jocala

Here's what I ended up with. I hope this working example helps someone else. If there's anythng wrong or it can be improved, please post.

@
void MainWindow::get_data() {
QNetworkRequest request;
request.setUrl(QUrl("http://www.example.com/version.txt"));

QNetworkAccessManager *nam = new QNetworkAccessManager();
QNetworkReply *reply = nam->get(request);

connect(reply, SIGNAL(finished()),
this, SLOT(onReqCompleted()));

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

   int err = reply->error();
   QString s2 = QString::number(err);
   QMessageBox::critical(0, "","Network error: " + s2,QMessageBox::Cancel);

}

void MainWindow::onReqCompleted() {
QNetworkReply *reply = qobject_cast<QNetworkReply *>(sender());
QByteArray data = reply->readAll();

QString s1(data);
s1 = strip(s1);
int err = reply->error();
QString s2 = QString::number(err);

   if (version != s1)
   {
       QMessageBox::StandardButton reply;
        reply = QMessageBox::question(0, "", "Version "+s1+" is ready. Download?",
                QMessageBox::Yes|QMessageBox::No);
          if (reply == QMessageBox::Yes)
           {
              QString link = "http://www.example.com/file.html";
              QDesktopServices::openUrl(QUrl(link));
            }

   }

   delete reply;

}

@

andreyc

Thank you for sharing your solution.

Comment:
You don't need to check a reply->error() in MainWindow::get_data()
It should be in MainWindow::onReqCompleted() before reply->readAll()

jocala

Thanks for the feedback.